ECOLOGY, THE AMAZON BARRIER, AND SPECIATION IN WESTERN ATLANTIC Halichoeres (LABRIDAE)
By
LUIZ A. ROCHA
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
2003 Copyright 2003
by
Luiz A. Rocha To my wife, Claudia, for her unconditional support and patience. ACKNOWLEDGMENTS
I would like to thank Brian Bowen for introducing me to the study of phylogeography, for letting me work in his lab, and for sharing his extensive knowledge and excitement with me. After Brian left to work on other seas, Debra Murie and Gustav
Paulay kindly accepted me as their student. I extend special thanks to Debra Murie, who has been very supportive and ensured that the genetics lab was an excellent place to work. Gustav Paulay provided me with constructive criticism, professional guidance and
friendship. I would like to thank the members of my committee (Carter Gilbert, Stephen
Karl, William Smith-Vaniz, and Colette St. Mary), all of whom contributed to the success of my research. Carter Gilbert’s deep knowledge of ichthyology has been a constant inspiration. Stephen Karl was always interested in my work, has supported me from the beginning, and financed two trips to the Bahamas. William Smith-Vaniz gave me full
access to his extensive library, and financed a trip to St. Croix, USVI. Colette St. Mary
always lent a hand when I needed it; and thoughtfully helped me clarify many portions of my research.
I thank D. Ross Robertson (the best fish collector I’ve ever met) for participating in most of the field trips, and critically reading most of my work. Anna Bass, Howard
Choat, Bruce Collette, Marcia Coura, Bertran Feitoza, Carlos Ferreira, Sergio Floeter,
Joao Luiz Gasparini, Zandy Hillis-Star, Daryl Parkyn, Brenda-Lee Philips, Jo Pitt,
Claudia Rocha, Ierece Rosa, Ricardo Rosa, David Snyder, Su Sponaugle, Benjamin
Victor and Doug Weaver obtained samples and helped in laboratory and field work.
IV Gerald Allen, Bertran Feitoza and Paul Humann allowed me to use their excellent underwater photographs. Discussions with Sergio Floeter, Craig Moritz, Ivan Sazima,
Geerat Vermeij and Mark Westneat greatly improved this work. Logistical support and/or collecting permits were provided by the Bermuda Biological Station for Research;
the Bermuda Fisheries Department; the National Park Service at St. Croix; the
Smithsonian Research Laboratory at Carrie Bow Cay, Belize; and the Brazilian Navy
Station at St. Paul’s Rocks.
Financial support for laboratory and field work was provided by the National
Science Foundation (through a grant to Brian Bowen); the Smithsonian Tropical
Research Institute; and PADI (Professional Association of Diving Instructors), Project
Aware. A doctorate scholarship was provided by CAPES (Fundacao Coordenacao de
Aperfeicoamento de Pessoal de Nivel Superior), Brazilian Ministry of Education.
v 1
TABLE OF CONTENTS Page
ACKNOWLEDGMENTS iv
LIST OF TABLES viii
LIST OF FIGURES ix
ABSTRACT x
CHAPTER
1 INTRODUCTION AND BACKGROUND 1
Wrasses of the Genus Halichoeres in the Atlantic 2 This Study 3
2 PATTERNS OF DISTRIBUTION AND PROCESSES OF SPECIATION IN BRAZILIAN REEF FISHES 5
Introduction 5 Methods 6 Discussion 8 Endemism in Brazilian Coastal Reefs: the Numbers 8 The Amazon Barrier 9
Speciation and the Amazon Barrier 1 The Caribbean region: A center of origin or accumulation? 15 Speciation in the Western Atlantic: Dispersal or Vicariance? 16 Environmental Differences Driving Species Distributions and Speciation on Brazilian Oceanic Islands 18 The Southern Oceanic Islands 21 Disjunct Distributions 22 Conclusions 24
3 ECOLOGICAL SPECIATION IN A CLOSELY RELATED REEF FISH SPECIES
PAIR (.Halichoeres : LABRIDAE) 26
Introduction 26 Materials and Methods 27 Results 30 Discussion 33
vi 4
5 CRYPTIC SPECIATION DRIVEN BY ENVIRONMENTAL CONDITIONS IN Halichoeres bivittatus (LABRIDAE) 38
Introduction 38 Methods and Materials 40 Results 40 Discussion 42
COLOR PATTERN VARIATION, AND THE PHYLOGEOGRAPHY OF FOUR SPECIES OF Halichoeres (LABRIDAE) IN THE WESTERN ATLANTIC 46
Introduction 46 Methods and Materials 49 Results 49 Halichoeres cyanocephalus 49 Halichoeres garnoti 50 Halichoeres maculipinna 52 Halichoeres poeyi 54 Discussion 56 Halichoeres cyanocephalus 56 Halichoeres garnoti 56 Halichoeres maculipinna 58 Halichoeres poeyi 59 Conclusion 60
6 GENERAL CONCLUSIONS 61
Reconciling Local Adaptation with the Pelagic Larval Stage 62 Conclusions 63
LIST OF REFERENCES 66
BIOGRAPHICAL SKETCH 77 1
3- LIST OF TABLES 4- Table page
4- 3-1. Sample size, number of haplotypes, haplotype diversity and nucleotide diversity of 5- the populations surveyed 31
2. Population pairwise Ost for Halichoeres brasiliensis and H. radiatus 3
1. Sample size, number of haplotypes, haplotype diversity and nucleotide diversity of the populations surveyed 41
2. Population pairwise Ost for Halichoeres bivittatus 42
1. Sample size, number of haplotypes, haplotype diversity and nucleotide diversity of the populations surveyed 51
5-2. Population pairwise Ost for Halichoeres garnoti 51
5-3. Population pairwise Ost for Halichoeres maculipinna 53
5-4. Population pairwise Ost for Halichoeres poeyi 55
viii LIST OF FIGURES
Figure PaSe 2- 2-1. Tropical western Atlantic 7 3-
2-2. Schematic view of the Amazon sediment deposition and freshwater discharge, 3- during stands of high and low sea level 10
2-3.4- Contours of species diversity of the families Labridae, Pomacentridae and Scaridae western Atlantic 16 4- in the tropical
5- 4. Operation of the Amazon barrier 18
1. Tropical western Atlantic 29
3-2. Phylogenetic tree of Halichoeres radiatus and H. brasiliensis haplotypes 32
3. Halichoeres brasiliensis at the Brazilian coast and Halichoeres radiatus at Fernando de Noronha 35
rubble bottom off eastern Florida and at the Bahamas. 39 1 . Halichoeres bivittatus over
2. Phylogenetic tree of Halichoeres bivittatus haplotypes 43
1. Halichoeres cyanocephalus at northeastern Brazil and Dry Tortugas, Florida 47
5-2. Halichoeres garnoti at Bermuda and St. Lucia 48
5-3. Halichoeres maculipinna at northeastern Brazil and the Bahamas 48
5-4. Halichoeres poeyi in a turbid coralline algae reef off northeastern Brazil 48
5-5. Phylogenetic tree of Halichoeres cyanocephalus haplotypes 50
5-6. Phylogenetic tree of Halichoeres garnoti haplotypes 52
5-7. Phylogenetic tree of Halichoeres maculipinna haplotypes 54
poeyi haplotypes 55 5-8. Phylogenetic tree of all (3 1 ) Halichoeres
IX Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy
ECOLOGY, THE AMAZON BARRIER, AND SPECIATION IN WESTERN ATLANTIC Halichoeres (LABRIDAE)
By
Luiz A. Rocha
August 2003
Chair: Debra Murie Major Department: Fisheries and Aquatic Sciences
Recent estimates indicate that about 12% of the Brazilian reef fish species are
endemic. Most ichthyologists agree that this endemism is generated by the barrier formed by the freshwater and sediment discharge of large rivers in northeastern South America
(mainly the Amazon, Orinoco and their tributaries). However, little is known about the dynamics of this barrier. Recent studies have shown that the barrier can be crossed through deep sponge bottoms on the outer continental shelf off northeastern South
America. Moreover, the recent discovery of species regarded as Brazilian endemics in the
extreme southern Caribbean is showing that the Amazon barrier is weaker than previously thought.
Two hypotheses were generated to explain the effects of the Amazon barrier on western Atlantic reef fish:
• The Amazon is a strong barrier to dispersal; but sea-level fluctuations influence the effectiveness of the barrier; and may greatly affect fish species diversity in the western tropical Atlantic.
x • Larval exchange between Brazil and the Caribbean is small but constant; contrasting selection pressures in divergent environments (continental Brazil versus insular Caribbean) may be the central force driving speciation.
To test these hypotheses, a total of 632 samples of seven species of Halichoeres were obtained from 13 locations across the western Atlantic. Although congruent population structure was expected in these species because of their similar dispersal potential and exposure to the Amazon barrier, varying degrees of genetic separation were observed.
The observed distribution of genetic partitions indicates that gene flow exists between environmentally similar, but geographically distant locations. Deep genetic divergences coincided with environmental differences between locations, regardless of distance or dispersal barriers. The pattern drawn from our study indicates that divergent environmental conditions can be as important as (or sometimes more important than) vast distances of unsuitable habitat (either open ocean waters or the area influenced by the
Amazon) in producing genetic partitions; and that benthic-stage habitat preferences may be strongly influencing the biogeography of western Atlantic reef fishes.
xi CHAPTER 1 INTRODUCTION AND BACKGROUND
The northeastern coast of South America (between the mouths of the Orinoco and
Amazon rivers) is characterized by soft bottoms, turbid waters, and the world’s largest
freshwater runoff (Curtin 1986). This area, known as the Amazon barrier, is recognized
as a barrier to the dispersal of reef-building corals (Cox and Moore 2000), rocky-shore gastropods (Vermeij 1978), and shallow-water reef fishes (Gilbert 1972). The presence of
this barrier and the endemism found in corals, hydrozoans, mollusks and fishes in Brazil
led Briggs (1974a) to consider the tropical Atlantic coast of Brazil and its oceanic islands a biogeographic province distinct from the Caribbean and the West Indian provinces. On the other hand, the limited data available on the Brazilian marine ichthyofauna and the
discovery of reef fishes under the Amazon freshwater plume (Collette and Rtitzler 1 977) led Helfman et al. (1997) to conclude that there was no evidence for such a division.
However, the Amazon barrier is not the only mechanism promoting speciation in
the western Atlantic. It is widely recognized that the distribution of reef fishes is also
strongly influenced by environmental characteristics. The Amazon itself is an
environmental barrier because it consists of a vast area without suitable habitat for
shallow reef organisms, and it does not preclude dispersal per se (Vermeij 1978). In the western Atlantic, differences between continental and insular faunas have been recognized and attributed to ecological rather than physical barriers (Gilbert 1972;
Robins 1971). Recently, Rocha et al. (2002) showed that adult habitat preferences may have a greater influence than distance or PLD on the genetic structuring of three
1 2
surgeonfish species with similar dispersal abilities, and Tringali et al. (1999)
demonstrated that genetic divergences are related to habitat preferences in transisthmian
species pairs of Centropomus. These observations have prompted a reevaluation of the
role of ecological factors in reef fish speciation.
Wrasses of the Genus Haliclioeres in the Atlantic
The distributions of pairs of sister species and intraspecific genetic partitions are
valuable for testing speciation hypotheses (Randall 1998; Knowlton 2000; Planes 2002).
The widely distributed wrasses of the genus Halichoeres are well-suited to test speciation
scenarios in the Atlantic because:
• They are distributed on both sides of a recognized barrier (the Amazon freshwater outflow, which precludes the development of coral reefs on the coast of northeastern South America);
• Most Atlantic Halichoeres have a similar mean pelagic larval duration (PLD) of 24 to 30 days (Sponaugle and Cowen 1997; Wellington and Robertson 2001), reducing the possibility of significant differences in dispersal potential of larvae;
• They have varying degrees of habitat specificity and preferences (Randall 1967, 1996).
With more than 70 described species, Halichoeres is the most species-rich genus of the family Labridae (Parenti and Randall 2000; Randall and Lobel 2003). Most species of this genus are diurnal, feed on mobile benthic invertebrates and inhabit tropical
shallow rocky shores, reefs and surrounding areas (Randall 1996; Randall et al. 1997).
There are eleven recognized species in the Atlantic. Six are restricted to either side of the
Amazon barrier: H. bathyphillus is known from Bermuda and the continental coast of
North America (Smith-Vaniz et al. 1999); H. brasiliensis is known from the continental
coast of Brazil and Trindade Island (Rocha and Rosa 2001b); H. caudalis is known from
the continental coast of North America (Humann and Deloach 2002); H. garnoti is H
3
known from the Caribbean, Bahamas, south Florida and Bermuda (Randall 1996); H.
pictus is known from the Caribbean and south Florida (Humann and Deloach 2002); and
H. socialis is known from inshore mangrove islands of the Belize barrier reef (Randall
and Lobel 2003).
The remaining five species (II bivittatus, H. cyanocephalus, H. maculipinna, H.
poeyi and H. radiatus) occur on both sides of the Amazon barrier: H. bivittatus is the
most abundant Halichoeres in the North Atlantic, and occurs in continental coasts and
oceanic islands from North Carolina and Bermuda to northeastern Brazil, including the
Bahamas and the Gulf of Mexico; H. cyanocephalus is a rare species that occurs in
Florida, the Greater Antilles, the continental coasts of central America, and northeastern
Brazil, and is absent from the Bahamas, Bermuda and the Lesser Antilles; H.
maculipinna occurs in Bermuda, the Bahamas, South Florida, the Caribbean Sea, the
tropical continental coast of Brazil and Trindade Island; H. poeyi is a common inshore
species that occurs from South Florida to South Brazil including oceanic islands, but is absent from Bermuda; H. radiatus occurs in the Caribbean Sea, the Bahamas, Bermuda,
Florida, the southern Gulf of Mexico, and also in the Brazilian oceanic islands of Atol das Rocas, Fernando de Noronha and St. Paul’s Rocks, 3000 km away from the
Caribbean. The closely related Brazilian endemic H. brasiliensis, until recently was considered a synonym of H. radiatus (Rocha and Rosa 2001b).
This Study
This dissertation is comprised of six chapters. In Chapter 2, the geological history
and oceanography of the barrier is Amazon analyzed in detail. In Chapters 3, 4 and 5, the results of a survey of the mitochondrial DNA (mtDNA) variation in populations of the seven most widely distributed western Atlantic species of the genus Halichoeres ( 4
bivittatus, H. brasiliensis, H. cyanocephalus, H. garnoti, H. maculipinna, H. poeyi and H. radiatus) are presented. Analysis of such variation can provide evidence to answer the following questions:
• Is the Amazon freshwater outflow a barrier to dispersal of western Atlantic Halichoeresl
• Based on the geographic distribution of mtDNA haplotypes, what speciation models best explain the evolutionary history of Halichoeres in the Atlantic?
• Do the color differences between closely related species (H radiatus and H. brasiliensis) and allopatric populations (H. garnoti in the Caribbean versus Bermuda, H. cyanocephalus in the Caribbean versus Brazil, and H. maculipinna in the Caribbean versus Brazil) reflect molecular evolutionary partitions?
Chapter 3 an analysis is presented of genetic partitions within the closely related species pair H. radiatus and H. brasiliensis to address the three questions above. Chapter
4 is focused on the correlation between color and genetic differences in H. garnoti, H. cyanocephalus and H. maculipinna. Chapter 5 is a population genetic survey of H. bivittatus. Chapter 6 summarizes this study and provides direction for further research. CHAPTER 2 PATTERNS OF DISTRIBUTION AND PROCESSES OF SPECIATION IN BRAZILIAN REEF FISHES
Introduction
As pointed out by Randall (1998), the analysis of shore fish distributions can elucidate the placement of geographical barriers and their role in speciation. Processes
leading to the high diversity of the Indo-Pacific tropical region have been studied in detail
(Ormond and Roberts 1997; Briggs 1999). Less attention has been devoted to
zoogeographical patterns in the tropical western Atlantic. The goal of this chapter is to evaluate the role of biogeographic barriers, especially the Amazon River, in influencing the speciation of reef-associated organisms in the shallow tropical western Atlantic, mainly by analyzing species and population distribution patterns, the barrier’s geological history, and its past and present oceanographic characteristics. Historical and ecological factors were considered and may explain much of the evolutionary dynamics in widely distributed western Atlantic reef fishes.
The northeastern coast of South America (between the mouths of the Orinoco and
Amazon rivers) is characterized by soft bottoms, turbid waters, and the world’s largest freshwater runoff (Curtin 1986). This area is recognized as a barrier to the dispersal of reef-building corals (Cox and Moore 2000), rocky-shore gastropods (Vermeij 1978), and shallow-water reef fishes (Gilbert 1972). The endemism found in corals, hydrozoans, mollusks and fishes in Brazil led Briggs (1974a) to consider the tropical Atlantic coast of
Brazil and its oceanic islands a biogeographic province distinct from the Caribbean and
5 6
the West Indian provinces. On the other hand, the limited data available on the Brazilian
marine ichthyofauna and the discovery of reef fishes under the Amazon freshwater plume
(Collette and Rutzler 1977) led Helfman et al. (1997) to conclude that there was no
evidence for such a division.
However, in the past few years a large amount of data on Brazilian reef fishes
became available, including species descriptions (Sazima et al. 1998; Rocha and Rosa
1999; Heiser et al. 2000; Gasparini et al. 2001; Moura et al. 2001); redescriptions and revalidations of fishes endemic to Brazilian reefs (Rocha et al. 2001; Rocha and Rosa
2001b); faunal surveys (Rocha et al. 1998; Gasparini and Floeter 2001; Rocha and Rosa
2001a); and consequently zoogeographic analyses (Floeter and Gasparini 2000; Floeter et al. 2001; Joyeux et al. 2001). This increase in knowledge about western South Atlantic reef fishes was augmented by the discovery in the southern Caribbean (Rocha 2002) of several fish species previously considered to be Brazilian endemics. These findings warrant a re-examination of distribution patterns and speciation processes in tropical western Atlantic reef fishes.
Methods
It is difficult to define a reef fish (Bellwood and Wainwright 2002). For this reason species lists and numbers (and thus biogeographic analyses) vary considerably depending
on what the authors consider reef fish. The discussion herein is focused on tropical fishes and other organisms associated with reef or hard substrate, distributed to depths of up to
100 m. The distributions of tropical reef fishes in the western Atlantic ranges from
Bermuda (35°N; Robins 1971) to Santa Catarina (in southern Brazil, 28°S; Floeter et al.
2001). Locations of interest, major currents, and the Amazon barrier are shown in Figure
- 2 1 . 7
90° 75° 60° 45° 30°W
Figure 2- 1 . Tropical western Atlantic. Approximate area of influence of the Amazon barrier shaded in grey. Underlined numbers represent locations mentioned in
the text: 1. Tobago. 2. Manuel Luiz reefs. 3. St. Paul's Rocks. 4. Fernando de
Noronha and Atol das Rocas. 5. Abrolhos reefs. 6. Trindade Island. Arrows indicate direction of mean surface oceanic currents, except for the ECC,
which is a sub-surface current. Current abbreviations: GS = Gulf Stream. NEC = North Equatorial Current. ECC = Equatorial Countercurrent. NBC = North Brazil Current. SEC = South Equatorial Current. BC = Brazil Current. Dotted line shows approximate location of continental shelf break.
Species distributions were obtained from the scientific literature (Rosa et al. 1997;
Rocha et al. 1998; Feitoza 1999; Rocha et al. 2000; Gasparini and Floeter 2001; Rocha
and Rosa 2001a) and analysis of preserved material in the following fish collections:
Ichthyological Collection at the Universidade Federal da Paraiba, Brazil (UFPB), Museu 8
de Zoologia da Universidade de Sao Paulo, Brazil (MZUSP), Florida Museum of Natural
History at the University of Florida (UF), National Museum of Natural History at the
Smithsonian Institution (USNM), and Museum of Comparative Zoology at Harvard
University (MCZ). Recent phylogeographic analyses (e.g., Muss et al. 2001; Rocha et al.
2002) provided additional information about population structure within species
distributed through coastal Brazil and the Caribbean.
Discussion
Endemism in Brazilian Coastal Reefs: the Numbers
Recent inventories of Brazilian marine fishes give totals of 844 (Szpilman 2000) or
962 (Carvalho-Filho 1999) species. However, these lists include many vague records, based on popular Caribbean fish guides, which frequently state that some widely distributed species range “south to Brazil”. A more realistic list (based on collections and literature records) compiled by Rosa et al. (in press) recorded 518 shore fishes from the northeastern Brazilian continental shelf. An estimated 323 of these species occur in or around coral or rocky reefs. Adding this number to the reef fishes of southeastern Brazil
(S. R. Floeter and J. L. Gasparini, pers. comm.), a total of 353 reef fishes is obtained.
This seems to represent a realistic number, and is roughly half of the number of reef fishes found in the richer Caribbean region (Lieske and Myers 1994; Smith 1997).
Forty-five (12.7%) of the fish species found on reefs at the Brazilian shelf are not found in other biogeographic provinces, and are thus considered endemics. This level of
endemism is less than previous estimates of 1 8% (Jouyeux et al. 2001); mainly because analyses of collections and underwater photographs from the southern Caribbean (Rocha
2002) revealed that many species previously considered Brazilian endemics also occur in 9
that region. Oceanic island endemics contribute to the endemism at their respective
islands, and not the Province; so they are not among the 45 species cited above.
The Amazon Barrier
In present times (interglacial interval, high sea level), the Amazon discharges about
one-fifth of the world’s total freshwater runoff into the Atlantic (Curtin 1986), or 6,300
J 1 km year' (Milliman and Meade 1983); and the largest riverine sediment discharge (2.9 x
1 108 tons year' ) into the world ocean (Degens et al. 1 991). The outflow is so large that
seawater never enters the river mouth, and freshwater is transported offshore as a surface
plume (Nittrouer and DeMaster 1986), up to 500 km seaward (Lentz 1995). This surface
freshwater plume extends to a depth of ca. 30 m over the Amazon area shelf, and subsurface ocean water is restricted to depths greater than 30-40m over the outer shelf
(Curtin and Legeckis 1986; Masson and Delecluse 2001). During the current interglacial
period, most of the sediment carried by the Amazon is not deposited over the outer shelf, but is diverted towards the Guyana’s shelf by the North Brazil Current (Figure 2-2),
where it forms extensive mud deposits up to 20 km wide, and 60 km long (Kuehl et al.
1986; Allison et al. 2000).
Sea-level fluctuations greatly influence the dynamics of the Amazon barrier.
Sediment distribution is quite different during glacial maxima, when the sea level can be
130 m lower than at present. During low sea level, the sediment from the Amazon is transported directly offshore through canyons in the continental shelf, and deposited in the Amazon deep-sea fan (Nittrouer and DeMaster 1986). This fan-shaped area extends
2 700km seaward and covers ca. 375,000 km at 1000 to 4300 m depths (Lopez 2001). The lower ocean-water layer of the continental shelf disappears, and low-salinity waters and
sediment carried by the Amazon maintain contact with the shelf until its edge, which can 10
be as shallow as 10 m with lower sea levels (Figure 2-2). Stratigraphic data obtained in the Amazon fan revealed that sedimentation rates during the last glacial period were 5 to
1 ky' 1 compared to about 0.1 m ky' in the present and previous interglacial periods 25 m ,
(Lopez 2001).
Figure 2-2. Schematic view of the Amazon sediment deposition (left), and freshwater discharge (right) during stands of high (top, present condition) and low sea level (bottom); NBC = North Brazil Current.
Age is a major issue in understanding the effects of the Amazon barrier on the
tropical western Atlantic shore fauna. There is some disparity about the Amazon
geological history in the current Brazilian reef fish literature. According to Joyeux et al.
(2001), the initial connection between the Amazon and the Atlantic was established at 5
to 6 million years ago (Mya), whereas Floeter and Gasparini (2001) stated that the 11
Amazon influence started at the point of maximum sediment deposition, 1.6 Mya.
However, the geological literature is clear; Potter (1997) and Hoorn (1994) state that the
origin of sediment deposition by the Amazon in the Atlantic is confirmed by the presence
of a large late Middle Miocene submarine fan (formed ca. 1 1 Mya), coinciding with a
major uplift of the Andes (Hoorn et al. 1995). Hoorn (1996) affirms that the connection
between the palaeo-Amazon and the Atlantic has been well established since the
beginning of the Late Miocene (10.4 Mya).
Speciation and the Amazon Barrier
The most important component of the classic model of allopatric speciation is the
formation of a barrier that divides a species’ range into isolated portions, so that gene
flow is eliminated; and (given enough time) genetic differences can accumulate (Brown
and Lomolino 1 998). If the vicariant barrier collapses, previously isolated populations
may be sufficiently divergent that intrinsic reproductive barriers (post mating isolation)
complete the process of speciation, even in renewed sympatry. This model is the
foundation for vicariance biogeography (Barton 1988).
The soft bottoms, combined with the freshwater surface plume of the Amazon and
high sedimentation, do not allow the development of coral reefs on the northeastern coast
of South America, separating the Brazilian from the Caribbean coral and reef-associated
faunas (Veron 1995; Cox and Moore 2000). Several authors recognized the influence of
this barrier in the formation of pairs of sister species of reef fishes in the western tropical
Atlantic: Apogon maculatus and A. americanus (Gilbert 1977); Stegastes adustus and S. fuscus (Greenfield and Woods 1974); Stegastes partitus and S. pictus (Emery 1973);
Thalassoma bifasciatum and T. noronhanum (Rocha et al. 2001); Lythrypnus mowbrayi 12
and L. brasiliensis (Greenfield 1988); and Starksia ocellata and S. brasiliensis (Williams and Smart 1983).
Furthermore, the Amazon barrier is believed to be responsible for the formation of geminate species pairs in shallow-water corals (Leao 1986) and rocky-shore gastropods
(Vermeij 1978). This barrier is also probably responsible for the deep DNA sequence divergences between Brazilian and Caribbean populations of the spiny lobster Panulirus argus (Sarver et al. 1998), the redlip blenny Ophioblennius atlanticus (Muss et al. 2001),
and the ocean surgeonfish Acanthurus bahianus (Rocha et al. 2002).
However, as noted by Gilbert (1977), a barrier to organisms that inhabit hard
bottom in shallow, clear seawater is not necessarily a barrier to deep-water reef fishes.
During periods of high sea level, the deep outer shelf in the Amazon region (50 to 70 m) has low sedimentation and normal salinity, allowing colonization by sponges and some deep-water reef fishes (Collette and Rutzler 1977). At the same time the surface freshwater plume creates low light conditions, precluding coral development. This narrow area can be used as a corridor between the Brazilian and Caribbean biogeographic provinces by organisms that require clear, normal salinity seawater but not shallow reef habitats or corals.
A recent survey of sponge dwelling fishes off northeastern Brazil (Rocha et al.
2000) recorded several Brazilian endemic reef fishes, including many of the ones listed above, living in sponge bottoms off northeast Brazil in similar depths to those explored by Collette and Rutzler (1977) off the Amazon mouth. Those Brazilian endemics that can live on deep sponge bottoms can potentially cross the Amazon barrier via the sponge corridor. If so, how can speciation occur in these groups? One possible explanation 13
involves oceanographic characteristics of the Amazon area shelf during Pleistocene glacio-eustatic cycles (Figure 2-2). The physical configuration of the Amazon barrier changes dramatically during low sea-level stands: the low-salinity waters and sediment are transported directly to the deep-sea fan in the Atlantic Ocean floor. This results in low salinity and high sedimentation conditions across the shelf, so that colonization by neither sponges nor reef fishes is possible; and the corridor between Brazil and Caribbean may be effectively closed during these intervals.
The geological record indicates that only rarely in the last 850 ky was the global
temperature as warm as it is in the present interglacial period (Gates 1993). The last glacial period (Wisconsin) lasted for at least 100 ky; the earth began warming around 18 ky BP, and the oceans reached their present level 6 ky BP, and have been stable since
then (Cox and Moore 2000). If a glacial period is long enough, or if a species is not able to cross the barrier during the short periods of high sea level, vicariant isolation and
speciation is possible.
In the Indo-Pacific, a dynamic barrier related to Pleistocene sea-level fluctuations was hypothesized by Randall (1998), and proposed as an explanation of distributions of
sibling species of reef fish. It is possible that sea level fluctuations also influence the speciation of western Atlantic reef fishes. As noted by Randall (1998) and Brown and
Lomolino (1998), barriers are not always static. Variations in sea level can produce successive isolations and connections of areas by creating land bridges during low sea-level stands, and later inundating those bridges with rising sea levels.
The intermittent (or semi-porous) nature of the Amazon barrier is indicated by the distribution of fish that occur primarily in Brazil, but also are found in sympatry with 14
closely related taxa north of the Amazon. The following closely related species pairs co-
occur in the southern Caribbean (Humann and Deloach 2002; Rocha 2002): Centropyge
argi and C. aurantonotus (Pomacanthidae), Priolepis hipoliti and P. dawsoni (Gobiidae),
Sparisoma chrysopterum and S. frondosum (Scaridae) and Stegastes partitus and S. pictus
(Pomacentridae). Since those pairs are very similar in general morphology, color (see
Humann and Deloach 2002) and ecological requirements (tentatively considered sister
species here), sympatric speciation in the southern Caribbean followed by colonization of
Brazil is unlikely. Also, most of the Brazilian components of those pairs are known to
occur in deep sponge bottoms in northeast Brazil (Rocha et al. 2000), indicating their
potential to use the sponge corridor under the Amazon outflow to cross the barrier
northwards; perhaps aided by the North Brazil Current which flows in a general south-
north direction along the Amazon area continental shelf (Peterson and Stramma 1991).
The present day distribution probably indicates secondary contact after range expansion
toward the southern Caribbean by the Brazilian component, probably through the sponge
corridor during an interglacial period.
Moreover, the following species are widely distributed in the Brazilian province
but recorded at only a few locations in the southernmost region of the Caribbean
province, possibly indicating speciation in the South Atlantic followed by recent crossing of the Amazon towards the Caribbean: Anisotremus moricandi (Haemulidae), Chromis
jubauna (Pomacentridae), Heteroconger Camelopardalis (Congridae), Opistognathus sp.
(Opistognathidae) and Ptereleotris randalli (Microdesmidae) (Rocha 2002). In contrast,
Chromis scotti (Pomacentridae), Coryphopterus thryx (Gobiidae), Haemulon melanurum
(Haemulidae), Halichoeres bivittatus (Labridae) (Rocha and Rosa 2001a) and Lutjanus 15
mahogoni (Lutjanidae) (Feitoza 1999) are widely distributed in the Caribbean, but are found only north of the “hump” of Brazil (above 10°S). These may be examples of recent crossing of the barrier southward.
The Caribbean region: A center of origin or accumulation?
Evidence indicates that the Caribbean also accumulates fauna. According to Briggs
(1974b), when a zoogeographic barrier separates two regions, “the region that develops the greatest ecosystem stability will function as the more important evolutionary center and will supply species to the lesser area but will accept few or no species in return”. This
seems to be happening in the Caribbean region, as it supplies many species to Brazil and receives only a few in return.
There is no doubt that the Caribbean region has the most diverse reef fish fauna in
the Atlantic, with more than 700 species; and is the center of diversity in the Atlantic
Ocean. Some of the most extreme examples are among New World genera that reach their greatest diversity in the Caribbean and are not present in the eastern Atlantic:
Elacatinus (Gobiidae) with 12 species in the Caribbean (Collin 1975) and two in Brazil;
Starksia (Labrisomidae) with at least 10 species in the Caribbean and two in the Brazilian coast (Rocha and Rosa 2001a); and the entire family Chaenopsidae with 9 genera in the
Caribbean (Randall 1996) and only two in Brazil (Ramos 1994; Ramos et al. 2003).
Figure 2-3 shows contour lines of diversity of the families Labridae, Pomacentridae and
Scaridae; most reef-associated groups in the western Atlantic show a similar pattern.
Recent faunal surveys in the southern Caribbean support the hypothesis that Brazil has exported a few species to the Caribbean. In this scenario, the center of diversity (the
Caribbean) is enriched by the introduction of species from a peripheral area (Brazil).
Thus the Caribbean may be a center of origin and at the same time a center of 16
accumulation, by receiving a few species from peripheral areas (Figure 2-4). Randall
(1998) and Paulay (1997) reached a similar conclusion to explain the high diversity of the
Indo-Malayan region.
90° 75° 60° 45° 30°W
Figure 2-3. Contours of species diversity of the families Labridae, Pomacentridae and Scaridae in the tropical western Atlantic.
Speciation in the Western Atlantic: Dispersal or Vicariance?
In dispersal models speciation proceeds by rare colonization across pre-existing
barriers; whereas in vicariance models, speciation is achieved by the appearance of
barriers fragmenting the ranges of widely distributed taxa (Humphries et al. 1988). 17
Interestingly, geminate reef fish species pairs separated by the Amazon (which started discharging large amounts of sediment and freshwater in the Atlantic ca. 10 Mya),
look more similar to each other than pairs separated by the Isthmus of Panama (which closed ca. 3 Mya; a clearly vicariant barrier). The dispersal model may explain this contradiction: many reef-fish species have the potential to cross long distances of open ocean during their pelagic larval stage; and sporadic dispersal between isolated
populations may retard the process of speciation (Avise 2000).
Intermittent vicariance can also explain the similarity between geminate species
pairs in the western Atlantic: considering the Amazon outer shelf as a corridor; and sea
levels as switches, opening and closing this corridor; vicariance may operate during low
sea levels, when the barrier is more efficient. When the barrier weakens and the corridor
re-opens in high sea level stands, some species can disperse; and isolated populations
may potentially coalesce (Bowen et al. 2001). However, if reproductive incompatibility is attained during one of the glacial periods, the geminate species will then follow distinct evolutionary paths.
A third (and more probable) explanation is that both fluctuations in sea level
(intermittent vicariance) and extended pelagic larval stage of some species (dispersal) decrease the effectiveness of the Amazon barrier (Figure 2-4). If we treat barrier effectiveness as a percentage (0% meaning free gene flow between populations, and
100% meaning complete isolation) a barrier that is 100% effective (the Isthmus of
Panama) would promote speciation much faster than a less effective barrier, such as the
Amazon area shelf. 18
T Barrier effectiveness 1
Figure 2-4. Schematic representation of the operation of the Amazon barrier on Species A. Letters represent points where reproductive isolation occurs, splitting the A lineage into species B-C, D-E and F-G. X represents extinctions, Y
coalescence. The sea-level curve is hypothetical and does not reflect the actual history.
Environmental Differences Driving Species Distributions and Speciation on Brazilian Oceanic Islands
All hypotheses above are based on the fact that an effective barrier has separated
Brazilian and Caribbean populations for a relatively long period. Another explanation for
speciation in western Atlantic reef fishes would be ecological speciation, which can occur without a physical barrier against dispersal. According to Schluter (2001) “ecological speciation occurs when divergent selection on traits between populations or subpopulations in contrasting environments leads directly or indirectly to the evolution of reproductive isolation”; either in allopatry, parapatry or sympatry. Mayr (1947) also recognized the importance of ecology in speciation, but regarded the process as much less frequent then geographic speciation. 19
The islands of the Caribbean Sea are characterized by clear waters all year round, relatively stable environmental conditions, and bottom sediments largely composed of
calcium carbonate (Robins 1971). In contrast, the northeastern Brazilian coast is a typical continental environment, with terrigenous substrates influenced by run off from rivers, and high turbidity caused by wind-driven suspension of bottom sediments (Leao and
Dominguez 2000). Those differences may generate divergent selection pressures in the
islands versus mainland habitats, potentially promoting ecological speciation, even in the
presence of some migration between populations.
Two groups of oceanic islands off Brazil appear to have similar environmental
conditions, except for a much lower coral diversity, to those found in the Caribbean. The
first and closer to the mainland are Fernando de Noronha Archipelago (340 km from the
coast) and Atol das Rocas (270 km from the coast). The second is the very isolated island
of St. Paul’s Rocks (1000 km from the coast), just a few km north of the Equator (Figure
2-1). Noronha and Rocas are probably formed by the Noronha hotspot, and the oldest
volcanic rocks in Noronha were aged between 8 and 10 My (Rivalenti et al. 2000). Thus,
if Rocas is formed downstream by the same hotspot, it would be a few million years
older. Saint Paul’s Rocks is located close to the mid-Atlantic ridge and two putative ages
are given for it: 9.5 Myr if it originated from a nearby ridge, or 35 Myr if it originated
from a farther oceanic ridge (Melson et al. 1972). They are all influenced by the warm
South Equatorial Current, and are located upstream from the Brazilian coast, with the
possible exception of St. Paul’s Rocks that is seasonally influenced by the Equatorial
Countercurrent (Figure 2-1, Edwards and Lubbock 1983). 20
Several fish species show a biogeographic link between the Caribbean and
is Brazilian oceanic islands. The puddingwife (Halichoeres radiatus, Labridae) widely
distributed in the Caribbean region, and is also found in the Brazilian oceanic islands of
St. Paul’s Rocks, Fernando de Noronha and Atol das Rocas, (Rocha and Rosa 2001b).
The puddingwife’s sister species, Halichoeres brasiliensis, is distributed throughout the
Brazilian tropical coast. A similar distribution is found in Elacatinus randalli, which is
found on the Caribbean and Fernando de Noronha off Brazil (Sazima and Moura 2000)
whereas E.figaro is endemic to the Brazilian coast. In addition, Haemulon chrysargyreum occurs in Fernando de Noronha, Atol das Rocas and the Caribbean, but is
absent from the Brazilian coast. If there is sufficient migration to morphologically
homogenize populations of H. radiatus and E. randalli separated by ca. 4000 km
(distance of open ocean between Atol das Rocas and the Caribbean), why can’t this gene
flow continue to the Brazilian coast, or why can’t H. chrysargyreum colonize the coast,
only 270 km away from Atol das Rocas?
Joyeux et al. (2001) suggested that this pattern might be a result of relictual
distribution of a once wider geographic range. However, I believe that the simplest
explanation is ecological speciation; the insular and coastal populations are subject to
divergent selection pressures that are sufficient to overwhelm the homogenizing effect of
sporadic gene flow. In extreme cases, environmental differences may prevent the
colonization of continental locations by strictly oceanic species (or vice-versa). Veron
(1995) proposed a similar hypothesis for the coral fauna of the Indo-West Pacific to
explain the greater similarity between widely separated locations with comparable
physical environments, than that of adjacent locations with different environments. He 21
concluded that environmental factors are more important than connectivity through currents and distance.
The distributions of some fishes in the north Atlantic may also be alternatively explained by the hypothesis of ecological speciation driven by environmental differences in continental versus insular habitats. The following species pairs show an insular versus continental distribution: Holacanthus ciliaris (common throughout the Caribbean,
Brazilian coast and islands) and H. bermudensis (mainly Gulf of Mexico and Florida, but hybrids between H. ciliaris and H. bermudensis are found in Bermuda); and Ptereleotris helenae (Caribbean islands) and P. caliurus (coastal Florida). The Gulf Stream has been tentatively considered a barrier between Florida and the Caribbean, however some of these taxa are found both sides of the barriers (like H. bermudensis at the Bahamas), weakening the hypothesis of vicariance. Moreover, the subspecies Stathmonotus stahli stahli (lesser Antilles) and S. stahli tekla (greater Antilles, coastal Central America and
Florida) are allopatric, but each occupies a wide geographic area, and there is no apparent barrier between their ranges.
The Southern Oceanic Islands
Oceanographic conditions at the Brazilian southern oceanic islands are very
different from those at the northeast. Trindade and Martim Vaz are located 1 160 km from the southeastern Brazilian coast, and are downstream from the coast, under the influence of the Brazil Current. They are the youngest Brazilian oceanic islands (3 - 3.5 Myr), and were subject to a recent faunal survey (Gasparini and Floeter 2001) and zoogeographical
study (Floeter and Gasparini 2000). There are six, relatively shallow (10 - 1 10m) seamounts between these islands and the mainland. The seamounts are about 250km 22
apart, and potentially increase the population connections between the islands and the mainland.
Floeter and Gasparini (2000) found a biogeographic split between the South
Atlantic oceanic islands and the ensemble of the Brazilian mainland, the Caribbean and
Bermuda using a cluster analysis. Their study was based on presence and absence of all reef associated fish species, and grouped Trindade Island with the northeastern Brazilian
oceanic islands. This was probably due to their similar total number of species, which is smaller than the remaining locations. In contrast, Rocha and Rosa (2001a) considered only distributions of labroid fishes and found the major division to lie between the North
and South Atlantic. Trindade was grouped with the Brazilian coastal sites, outside the
cluster formed by the northeastern Brazilian islands (St. Paul’s Rocks and Atol das
Rocas). Major current tracks (Figure 2-1), the presence of seamounts between Trindade
and the mainland and the close relationship between the island’s endemics and coastal
Brazil species (Gasparini and Floeter 2001) clearly indicate that Trindade is more closely
related to the Brazilian mainland than to the other Brazilian offshore islands.
Disjunct Distributions
Anti-tropical and disjunct distributions are well-known phenomena in Indo-Pacific
fishes, as reviewed by Briggs (1987) and Randall (1998). In the western Atlantic, Floeter
et al. (2001) noted that four serranids (Epinephelus niveatus, Mycteroperca microlepis,
M. tigris and Serranus phoebe) and one parrotfish (Sparisoma atomarium) were present
in southeastern Brazil and in the Caribbean, but absent or rare at the northeastern
Brazilian coast. Joyeux et al. (2001) stated that the wrasse Halichoeres bathyphillus and
the damselfish Chromis flavicauda present “strongly accentuated antitropical
distributions”. However, neither the wrasse, which is not H. bathyphillus, but a new 23
species probably endemic to southeastern Brazil (R. L. Moura, pers. comm.), nor the damselfish, which is abundant in and was described from low latitude waters (5°S)
(Rocha et al. 1998; Smith-Vaniz et al. 1999), seem to represent anti-tropical distributions.
There are at least three species that may have disjunct distributions, being abundant in southeast Brazil and the Caribbean, but absent from most of the NE Brazilian coast:
Mycteroperca microlepis (Serranidae), Sparisoma atomarium (Scaridae) and Chaetodon sedentarius (Chaetodontidae). The grouper M. microlepis may represent the only truly
anti-tropical distribution in Atlantic reef fishes: it is found in cold waters of the Gulf of
Mexico and northeast Florida, above the Tropic of Cancer (Humann and Deloach 2002), and from Espirito Santo, slightly above the Tropic of Capricorn (21°S) to Santa Catarina
(27°S), southeastern Brazil (Figueiredo and Menezes 1980), but has never been recorded at the Caribbean or northeastern Brazil.
The parrotfish S. atomarium is common in the Caribbean (Randall, 1996;
Humann and Deloach 2002) and southeastern Brazil (Joyeux et al. 2001), but apparently
absent from northeast Brazil (Rocha et al. 1998; Rocha and Rosa 2001a). The butterflyfish C. sedentarius occurs in the Caribbean (Randall 1996), Parcel de Manuel
Luiz reefs (Rocha and Rosa 2001a), and southeastern Brazil (Menezes and Figueiredo
1985), but was not recorded in the eastern region of northeast Brazil, or the “hump” of
Brazil (Rocha et al. 1998). Joyeux et al. (2001) suggested that this pattern is a consequence of the loss of the center of distribution, or tropical extinction, however the center of distribution of these species appears to be the Caribbean, not northeastern
Brazil. The geomorphology of the continental margin around the “hump” of Brazil may
offer clues to explain the absence of those species. The continental shelf in the area is 24
very narrow (22 - 30km), and relatively shallow (60 - 70m maximum depth) (Chaves
1979), thus the slope would be exposed during low sea levels, and habitat availability would be greatly reduced, probably causing extinction in many taxa.
Conclusions
The Amazon freshwater and sediment outflow is a strong barrier to shallow water
reef fish and other organisms, and it is probably responsible for most of the endemism
observed in Brazilian coastal habitats. However, during intervals of high sea level it can be crossed by fish that have broad habitat preferences, capable of living in deep sponge communities (50-70 m) off the Amazon outer shelf. The co-occurrence of closely related species pairs in the southern Caribbean indicates that speciation may occur during periods of low sea level, followed by dispersal across the barrier during high sea level. An
alternative (but not mutually exclusive) hypothesis is that there is continuous, but relatively small dispersal between Brazil and the Caribbean, and ecology plays a larger role in shaping diversity in the western Atlantic than previously thought, through divergent selection in environmentally different habitats.
There are two distinct groups of oceanic islands in Brazil, one in the northeast
corner, with strong oceanic characteristics, little influence from coastal waters, and affinities with the Brazilian mainland, the Caribbean and central Atlantic islands; and another in the southeast, strongly influenced by the coast, and with affinities mostly with the Brazilian mainland. The geomorphology of the continental shelf in northeast Brazil indicates that the few cases of disjunct distributions are probably better explained by extinction due to habitat loss during low sea level periods.
Despite recent advances in the knowledge of Brazilian reef fishes, there is still a need for reliable faunal surveys of the northeastern Brazilian coast and oceanic islands. 25
There is no recent checklist for fishes of Fernando de Noronha or Atol das Rocas, and recent visits to St. Paul’s Rocks by the author and colleagues indicate that several additions will be made to the checklist of Lubbock and Edwards (1981). Deep reefs off northeast Brazil are also understudied and may sustain a diverse reef fish community not seen on the adjacent near-shore, ecologically distinct reefs. The continental islands of the southern Caribbean (Trinidad and Tobago) form another area of interest that lacks reliable surveys. Once checklists from those areas are available, decisive evidence in favor of vicariance, dispersal and/or ecological speciation may become clear.
Comparative phylogeographic studies of closely related taxa may also contribute to the understanding of speciation processes in the tropical western Atlantic. Of special interest are the comparisons among taxa with varying levels of habitat preferences, but similar dispersal capabilities. If the pattern of genetic divergences strongly correlated to
habitat preferences observed by Rocha et al. (2002), is confirmed in other taxa, than the hypothesis of ecology as a driving force in reef fish evolution will be favored. Genus level phylogenies, either morphological or molecular, would also be welcome, especially
in groups where endemism is greater such as blennies and gobies, but the relationships are less obvious, possibly due to greater phylogenetic depth. Population genetics surveys of species that have disjunct distributions may reveal if those species were recently extinct in the narrow NE Brazil shelf or if they are relicts of a wider, older distribution. CHAPTER 3 ECOLOGICAL SPECIATION IN A CLOSELY RELATED REEF
FISH SPECIES PAIR (Halichoeres : LABRIDAE)
Introduction
Dobzhansky (1937) and Mayr (1942) proposed that geographical isolation (or allopatry) is a fundamental prerequisite for species formation. Following their line of thought, the most accepted speciation theories state that species are formed when an
ancestral population is split, by the erection of some geographical barrier, into isolated
populations, or when a few individuals found a population that is geographically isolated
from the ancestral species and that rapidly expands to fill the new area (Mayr 1982).
However, not all aspects of species diversity can be readily explained by allopatry, and examples of sympatric speciation are now abundant (Filchak et al. 2000; Mallet 2001;
Schluter 2001 ; Via 2001). Furthermore, speciation models proposed for terrestrial or freshwater organisms may not apply uniformly to marine organisms that inhabit a highly connected transglobal aquatic medium and have high dispersal potential (Palumbi 1992;
Knowlton 2000; Paulay and Meyer 2003).
This dispersal potential of many marine organisms is realized through a pelagic larval stage that can last from minutes to several months, and during which larvae may be dispersed by oceanic currents (Mora and Sale 2002). Pelagic larval duration (PLD) and other aspects of early life history are regarded as the most important influences in reef fish population genetics (Planes 2002). Despite the lack of correlation found by some studies between PLD and species’ geographic range (Victor and Wellington 2000), and
26 27
evidence that larvae can be retained close to their natal sites (Jones et al. 1999; Swearer et
al. 1999; Robertson 2001; Swearer et al. 2002), little attention has been given to other
factors that may affect the genetic structure and interconnection of fish populations, such
as adult habitat preferences and environmental characteristics.
In the western Atlantic, differences between continental and insular faunas have
been recognized and attributed to ecological rather than physical barriers (Robins 1971;
Gilbert 1972). Continental coasts have environmental conditions very different from those found at oceanic islands: continental reefs are mainly rocky or built by coralline
algae with little coral growth; the water is turbid during most of the year; the bottom
sediment is fine, terrigenous and frequently resuspended; and there is abundant
freshwater and sediment runoff. Oceanic islands have constantly clear waters; insular
reefs are mainly built by corals; the bottom sediment is mainly composed of calcium
carbonate; and there is little or no impact from river runoffs (Robins 1971).
In the western Atlantic, a pair of sister species seems to fit the insular versus
continental distribution. Halichoeres radiatus (Labridae) is found on reefs at Caribbean
and Brazilian oceanic islands and “island-like” locations (reef at outer shelves, far from
continental influences), whereas H. brasiliensis, its sister species, is found on inshore
reefs at the Brazilian continental shelf. This chapter aims to evaluate genetic partitions
within and between the insular and continental habitats, thus testing the hypothesis of
differentiation driven by habitat differences.
Materials and Methods
The entire geographic range of Halichoeres brasiliensis and H. radiatus was
sampled. Fishes were collected with pole spears or hand nets while scuba diving or
snorkeling in Bermuda, Florida Keys, Belize, St. Croix (USVI), Venezuela, coastal Brazil 28
(northeastern and south), Fernando deNoronha, St. Paul’s Rocks and Trindade Island
(Figure 3-1; Table 3-1). Samples were collected between 1997 and 2002. Tissue (muscle
and/or gill) was stored in a saturated salt-DMSO buffer (Amos and Hoelzel 1991).
Total genomic DNA was extracted using QIAGEN Dneasy extraction kits
following the manufacturer’s protocol. Extracted DNA was frozen in TE or AE buffer
and archived at -20°C. Primer names indicate the DNA strand (H = heavy and L = light
strand) and the position of the 3’ end of the oligonucleotide primer relative to the human
mitochondrial DNA sequence. A segment of approximately 800 base pairs of the
mtDNA cytochrome b gene was amplified with the primers L14725 (5’ GTG ACT TGA
AAA ACC ACC GTT G 3’) and HI 5573 (5’ AAT AGG AAG TAT CAT TCG GGT
TTG ATG 3’), which were also successfully used in other fish (Meyer 1993). These
primers did not work consistently among species, so the internal primers LI 4768 (5’
ACC CAC CCA CTC CTT AAA ATC 3’) and HI 5496 (5’ TTG GAG ACC CAG ATA
ATT TCA C 3’) were designed. They worked consistently among Halichoeres species and yielded a product of 709 base pairs.
Thermal cycling in polymerase chain reactions (PCR) consisted of an initial
denaturing step at 94°C for 1 min 20 sec, then 35 cycles of amplification (40 sec of denaturation at 94°C, 30 seconds of annealing at 52°C, and 55 sec of extension at 72°C),
and a final extension of 2 min 30 sec at 72°C. Excess primers were removed through
simultaneous incubation of PCR product with exonuclease I and shrimp alkaline
phosphatase (USB Corp., Cleveland OH).
Sequencing reactions with fluorescently-labeled dideoxy terminators (BigDye) were performed according to manufacturer’s recommendations, and analyzed with an 29
ABI 377 automated sequencer (Applied Biosystems, Inc. Foster City, CA). All samples were sequenced in the forward direction (with LI 4725 or LI 4768 primers), with rare and
questionable haplotypes sequenced in both directions to ensure accuracy of nucleotide designations.
Figure 3-1. Tropical western Atlantic. Approximate area of influence of the Amazon outflow shaded in grey. Underlined numbers represent sampling locations
from north to south, as follows: 1. Bermuda; 2. Gulf of Mexico; 3. Bahamas,
4. Florida Keys; 5. Belize; 6. St. Croix; 7. Venezuela; 8. Panama; 9. St. Paul's Rocks; 10. NE Brazil; 11. Fernando de Noronha; 12. SE Brazil; 13. Trindade Island. Current abbreviations as in Figure 1-1.
Sequences were aligned and edited with Sequencher version 3.0 (Gene Codes
Corp., Ann Arbor, MI). Population structure and gene flow were assessed with an 30
analysis of molecular variance (AMOVA, Excoffier et al. 1992) in the program Arlequin
v2.0 (Schneider et al. 2000), which generated ®ST values (a molecular analog of F St that takes into consideration sequence divergence among haplotypes). Genetic variation is
described with nucleotide diversity (tt; equation 10.19 in Nei 1987) and haplotype
diversity (/i; equation 8.5 in Nei 1987) within each location.
The computer program MODELTEST version 3.06 (Posada and Crandall 1998) was used to determine the substitution model that best fit the data through either a
minimal theoretical information criterion (AIC) or a hierarchical likelihood ratio test
(HLRT). The Tamura-Nei model (Tamura and Nei 1983) with a proportion of invariable
sites (I) of 0.82 was chosen. These values were used to estimate sequence divergences ( d
values) between haplotypes and to calculate ®St- Equal weighting of all three codon
positions was used. Relationships between common haplotypes and closely related
species were estimated using maximum parsimony with PAUP* version 4.0bl0
(Swofford 2002). The tree of relationships between haplotypes was drawn based on
starting trees calculated using the neighbor-joining methods and further searched by 10
tree bisection and reconnection (TBR) iterations under the minimum evolution criterion.
Results
A 709 bp segment from the cytochrome b gene was analyzed from 138 individuals (22
H. brasiliensis and 116 H. radiatus). A total of 21 polymorphic sites distributed among
23 haplotypes were identified for H. radiatus, and four polymorphic sites distributed
among five haplotypes for H. brasiliensis. Mean nucleotide frequencies in H.
brasiliensis were A=0.22, C=0.31, G=0. 1 7, T=0.30, and in H. radiatus A=0.23, C=0.32,
- G=0.16, T=0.29. The proportion of invariable sites was 0.75, and the transition 31
transversion ratio was 15.1:1. Pairwise distances between populations ranged from 0.17
= to 1.41 mean nucleotide substitutions ( d 0.001 to 0.004 sequence divergence) within species, and from 17.86 to 18.70 mean nucleotide substitutions (d = 0.023 to 0.026
sequence divergence) between species. Haplotype diversity (h ) was low in H. brasiliensis', the most common haplotype was present in 17 of the 22 individuals sampled. The Florida population of H. radiatus had the higher haplotype diversity,
whereas the St. Paul’s Rocks population had the lower. Overall nucleotide diversity (ti)
was low in all populations of both species (Table 3-1).
Table 3-1. Sample size, number of haplotypes, haplotype diversity and nucleotide diversity of the populations surveyed. N haplotypes h n
Halichoeres brasiliensis Brazil 22 5 0.41±0.10 0.00210.001 Total 22 5 Halichoeres radiatus Belize 19 7 0.76±0.09 0.00210.001 Bermuda 28 6 0.72±0.06 0.00210.001 Fernando de Noronha 7 3 0.53±0.21 0.00110.001 Florida Keys 6 5 0.9310.12 0.00310.002
St. Croix 23 8 0.7410.08 0.00210.001
St. Paul’s Rocks 24 3 0.2310.11 0.00110.001 Venezuela 9 5 0.8910.07 0.00310.002 Total 116 23
Table 3-2. Population pairwise
Locations 1 2 3 4 5 6 7 8
1. Bermuda 0
2. Florida 0.065 0
3. Belize 0.064 -0.068 0
4. St. Croix 0.029 -0.026 -0.008 0
5. Venezuela 0.069 -0.079 -0.030 0.013 0
6. N Brazil 0.938* 0.944* 0.937* 0.943* 0.940* 0
7. St. Paul’s 0.578* 0.656* 0.575* 0.596* 0.620* 0.967* 0 32
8. Noronha 0.167* 0.155 0.132 0.146* 0.143* 0.957* 0.695* 0
Significant population structure was observed within H. radiatus primarily due to
the St. Paul’s Rocks population, which is characterized by a single diagnostic mutation.
Pairwise 0 St values for St. Paul’s Rocks range from 0.604 to 0.802. No significant differences were observed among the other five locations (Fernando de Noronha,
Venezuela, Belize, St. Croix and Bermuda), separated by open ocean distances of up to
3845 km (Figure 3-1; Table 3-2).
Figure 3-2. Phylogenetic tree of all (27) Halichoeres radiatus and H. brasiliensis haplotypes. Geographical locations of haplotypes are: A. coastal Brazil; B. St. Paul’s Rocks and Fernando de Noronha; C. Caribbean, Florida and Bermuda. Some examples of distance barriers (more than 1000 km), one ecological barrier (turbid coastal Brazilian reefs versus clear water Caribbean and Atlantic reefs) and the Amazon barrier are indicated by dashed lines. Branch lengths are according to indicated scale; the branch leading to the outgroup (H. bivittatus) was reduced by 50%.
The phylogenetic analysis of the haplotypes of Halichoeres radiatus and H.
brasiliensis (Figure 3-2) shows that the species pair is reciprocally monophyletic. There 33
is no evolutionary distinction between populations of H. radiatus at the Brazilian oceanic
islands of Fernando de Noronha and St. Paul’s rocks (lineage B in Figure 3-2) and those at the Caribbean (lineage C in Figure 3-2).
Discussion
The most surprising result of the genetics of this species pair was the lack of deep
divergence among Brazilian offshore islands (Fernando de Noronha and St. Paul’s
Rocks) and the North Atlantic sites, separated by ca. 4500 to 5400 km of open-ocean and the Amazon barrier. Perhaps larval transport from Fernando de Noronha to the North
Atlantic is possible through the North Brazil Current, which flows northwards into the
Caribbean. However, passive transport southward from the Caribbean to Brazil may involve a circuitous rout, and timeframes much longer than the 26 days that H. radiatus can remain in the plankton: larvae would have to travel east on the North Atlantic gyre, travel south via the Canary Current, and only then make a possible westward connection to Brazil with the South Equatorial Current.
Alternatively, the recent discovery of eddies formed by the North Brazil Current in
the North Atlantic and the Caribbean (da Silveira et al. 2000) may provide a more direct route. These eddies could seasonally feed into the subsurface Equatorial Countercurrent,
potentially bringing larvae from the southern Caribbean to St. Paul’s Rocks, Fernando de
Noronha and the northeastern Brazilian coast. This possibility is speculative, but the congruent morphological and genetic similarities between H. radiatus at the Brazilian oceanic islands and the Caribbean indicate that this hypothesis cannot be discarded. Even rare pulses of southward dispersal would be important on the evolutionary timescale considered here. 34
Noronha and St. Paul’s are relatively equidistant from the Caribbean sites; however
H. radiatus at the former location shares haplotypes with samples from St. Croix and
Bermuda, whereas the latter location was distinguished by a diagnostic mutation. An explanation to that may lie on the geographic characteristics of St. Paul’s: contrarily to
Noronha, which is a relatively large island (13 km across, with a shelf 15 km wide along
the windward side) the exposed portion of St. Paul’s Rocks is less than 400m across, and
2 the area of shallow water (less than 50m deep) is less than 0.5 km (Edwards and
Lubbock 1983). It is a very small target for a larva drifting in the ocean, and it is possible that a very small number of larvae successfully seeded the population in St. Paul’s. The very low haplotype diversity (two haplotypes among 23 individuals; h = 0.16) also indicates a recent population expansion. These indications are compatible with a founder effect, which happens when a few individuals found a new population that is
geographically isolated from the ancestral species and that rapidly expands to fill the new area.
Within H. brasiliensis, the most common haplotype was shared between Paraiba,
Guarapari and Trindade Island, the three locations sampled in Brazil. Despite the
presence of the Sao Francisco River mouth, a potential barrier between Paraiba (NE
Brazil, Figure 3-1) and Guarapari (SE Brazil, Figure 3-1), the strong southwards flow of
the Brazil Current (BC, Figure 3-1) and very similar environmental conditions on both
sides of the potential barrier are cohesive forces that evidently overwhelm any isolation
effects of the Sao Francisco River outflow. Trindade is an oceanic island located
approximately 700 km east from the Brazilian coast (Figure 3-1). Genetic connections 35
between Trindade and the coast may be strengthened by the flow of the Brazil current
(BC, Figure 3-1) and by the presence of five sea mounts between the island and the coast.
The average divergence of 2.4% between H. radiatus and H. brasiliensis is similar
to that of many closely related pairs of fish species (Johns and Avise 1998). The fixed
divergence is congruent with morphological (Rocha and Rosa 2001) and color
differences (Figure 3-2), reinforcing the specific status of H. brasiliensis. A conventional
molecular clock for animal mtDNA of 2% per million years for the cytochrome b gene
(Avise 2000) suggests that this divergence is ca. 1 .2 my old, much younger than the
estimated age of the initial connection of the Amazon with the Atlantic (10 myBP)
(Chapter 1). This freshwater outflow is regarded in the literature as the isolating
mechanism driving the formation of sibling species pairs in the western Atlantic, with
one of the species distributed south of the barrier, off Brazil, and the other to the north,
through the Caribbean (Joyeux et al. 2001). The estimated divergence time is not congruent with the origin of the Amazon barrier under none of the conventional clock hypotheses, weakening arguments for a vicariant origin of the H. radiatus and H. brasiliensis pair.
Figure 3-3. Halichoeres brasiliensis at the Brazilian coast (A, photo by Gerald Allen) and Halichoeres radiatus at Fernando de Noronha (B, photo by Luiz Rocha). 36
Geographic distributions also do not support the hypothesis that genetic partitions are driven by isolation by the Amazon barrier. As noted by Rocha and Rosa (2001b), the populations at Fernando de Noronha and St. Paul’s Rocks, both located south of the
Amazon, are H. radiatus, the putative northern component of the sibling species pair.
Moreover, five individuals at the Fernando de Noronha population have a haplotype that is widely distributed and common in Caribbean populations. The placement of putative barriers on a phylogenetic tree of H. radiatus haplotypes clearly illustrates the incongruence between genetic partitions and dispersal barriers (Figure 3-2). That raises
an interesting question: if isolation by the Amazon barrier is not apparent, which speciation scenario is most compatible with the connection between Noronha and the
Caribbean (ca. 4000 km apart), and the separation between Noronha and the Brazilian coast (ca. 340 km apart)?
Allopatric speciation in populations north and south of the Amazon followed by
recent colonization of the offshore islands of Fernando de Noronha and St. Paul’s rocks may provide one explanation. Alternatively, ecological speciation driven by environmental differences between continental and insular locations may explain the observed pattern. Ecological speciation is defined as a process where divergent natural selection, either in contrasting habitats or different niches within the same habitat, leads directly or indirectly to genetic divergence and consequently reproductive isolation
(Mallet 2001; Schluter 2001).
The Brazilian coast has environmental conditions very different from those found
at oceanic islands: it has turbid waters during most of the year, fine terrigenous sediment
bottom that is frequently resuspended by the wind and is subject to freshwater runoff 37
(Leao and Dominguez 2000). The oceanic islands (St. Croix and Bermuda) have
constantly clear waters, calcium carbonate sediments and little impact from river runoffs
(Robins 1971). Considering those contrasting environmental conditions, the Brazilian islands (Noronha and St. Paul’s) are more similar to the North Atlantic and Caribbean oceanic islands than to the nearby Brazilian mainland.
Assuming small but constant larval interchange between the Brazilian coast, the
Brazilian oceanic islands, and the Caribbean, the speciation model that best explains the observed pattern is the ecological. In this scenario, divergent selection pressures in contrasting environments (continental versus insular) overcame the effects of migration. CHAPTER 4 CRYPTIC SPECIATION DRIVEN BY ENVIRONMENTAL CONDITIONS IN Halichoeres bivittatus (LABRIDAE)
Introduction
Many marine fish species have been considered to have geographically wide
distributions. This was supported by the presence of a planktonic larva that can
potentially disperse long distances (Mora and Sale 2002). However, recent studies on
larval behavior (Leis and McCormick 2002) and oceanographic processes (Cowen 2002)
indicate that larvae often disperse far less than their potential. Moreover, habitat selection
by larvae can also overcome the effects of long-distance dispersal and give rise to genetic
differences in geographically close populations (Bieme et al. 2003). Consequently,
genetic studies of widely distributed taxa often revealed the presence of cryptic species
(Knowlton 2000).
Thus, the genetic survey of widely distributed marine species may reveal the
presence of cryptic species. Halichoeres bivittatus is distributed across thousands of
kilometers of tropical and subtropical shores. It occurs in continental coasts and oceanic
islands from North Carolina and Bermuda to northeastern Brazil, including the Bahamas
the and Gulf of Mexico, and is the most abundant Halichoeres in the North Atlantic. It is the only representative of the genus to occur in the subtropical waters of the northern
Gulf of Mexico and North Carolina. Due to its wide distribution and extremely variable color pattern (Figure 4-1; Humann and Deloach 2002), several different scientific names were given to H. bivittatus (Randall and Bohlke 1965).
38 39
Figure 4-1 . Halichoeres bivittatus over rubble bottom off eastern Florida (A) and at the Bahamas (B; both photos by Luiz Rocha).
A prior mtDNA survey of H. bivittatus (Shulman and Bermingham 1995) revealed
no population structure among six locations throughout the Caribbean (Belize, Panama,
Curafao, Barbados, St. Croix, Bahamas). However, the Gulf of Mexico and northeastern
Brazil were not sampled. These areas known to contain evolutionarily divergent lineages
in other marine species (Avise 1992; Gold and Richardson 1998; Rocha 2002). Aiming
to detect previously unnoticed patterns, samples of H. bivittatus were collected from its
entire distribution range. A second objective of this study was to evaluate the
effectiveness of the Amazon as a dispersal barrier. The Amazon apparently separates
populations of other reef-associated species (Sarver et al. 1998; Rocha 2002; Chapter 2), and it can potentially cause cryptic speciation.
Temporal variation in the reproductive success of small subsets of adults may generate genetic differences, a phenomenon known as “sweepstakes effect” (Li and
Hedgecock 1998). Significant population genetic structure was previously observed in reef fishes and attributed to temporal variations (Lacson and Morizot 1991). Aiming to evaluate if such temporal variations were affecting the genetic structure of H. bivittatus, samples from different cohorts (larvae and adults) were collected. d
40
Methods and Materials
The entire geographic range of Halichoeres bivittatus was sampled. The fish were
collected with pole spears or hand nets while scuba diving or snorkeling in Bermuda, the
Bahamas, Florida Keys, Cedar Key (northwestern Florida), Belize, St. Croix (USVI),
Panama, Venezuela, and coastal Brazil (northeastern) (Figure 3-1; Table 4-1).
The techniques and protocols used for tissue preservation, DNA isolation, PCR
amplification and purification, sequencing analysis, selection of model of evolution and
phylogenetic reconstruction were the same as those in Chapter 3. The Tamura-Nei model
(Tamura and Nei 1983) with gamma distribution shape parameter of 0.01 was chosen.
Results
A 707 bp segment from the cytochrome b gene was analyzed from 216 individuals.
A total of 108 polymorphic sites distributed among 107 haplotypes were identified. The
— transition transversion ratio : was 6.37 1 . Mean nucleotide frequencies were A=0.22,
C=0.31, G=0.17, T=0.30. Two lineages separated by 30.68 to 32.04 mean nucleotide
substitutions ( = 0.042 to 0.045 sequence divergence) were observed. Distances within
lineages ranged from 0.02 to 4.25 mean nucleotide substitutions (d = 0.001 to 0.006
sequence divergence). Haplotype diversity (h) was relatively high and overall nucleotide
diversity (n) was low in all populations of both lineages (Table 4-1). No evidence of
temporal subdivision (sweepstake recruitment) was observed in H. bivittatus, as evident
from the low and not significant Ost values between two different cohorts (Keys Adult
versus Keys Larvae on Table 4-2).
Sample locations at the periphery of the species range revealed a deeply divergent
= mtDNA lineage within H. bivittatus (d 4.2% at the Gulf of Mexico, Florida Keys and 41
Bermuda; Figure 4-2), and significant population structure (at northeastern Brazil),
previously undetected by Shulman and Bermingham (1995). As noted by McCafferty et
al. (2002), broader geographical sampling designs often reveal previously unnoticed
patterns.
Significant population structure was observed across the tropical range of H.
bivitattus pairwise :
from 0.378 to 0.918 (Table 4-2). No significant differences were found between
locations within the Caribbean Sea separated by geographic distances of up to 2,000 km,
an observation similar to that of Shulman and Bermingham (1995).
The phylogenetic analysis (Figure 4-2) assigned the haplotypes of Halichoeres bivittatus into three lineages (lineages B, C and D). Lineage B mostly contains individuals from tropical locations. Lineage C is restricted to the subtropical Gulf of
Mexico, Florida Keys and Bermuda and D is found only in Bermuda. There was shallow separation between the lineages in Brazil and the Caribbean (lineages A and B).
Table 4-1 . Sample size, number of haplotypes, haplotype diversity and nucleotide diversity of the populations surveyed.
N haplotypes h 71
Bahamas 10 8 0.93±0.08 0.00310.002 Belize 30 14 0.69±0.09 0.00210.001 Bermuda 25 19 0.97±0.02 0.02310.012 Brazil 10 5 0.80±0.10 0.00210.001 Florida (Cedar Key) 13 11 0.96+0.05 0.00610.003 Florida Keys (adults) 28 21 0.95±0.03 0.02610.013 Florida Keys (larvae) 25 14 0.88±0.05 0.02610.013 Panama 24 10 0.6210.12 0.00210.001 St. Croix 31 16 0.8010.07 0.00410.002 Venezuela 20 13 0.9110.05 0.00410.002 Total 216 107 42
Table 4-2. Population pairwise Ost for Halichoeres bivittatus. Asterisks indicate significance at p=0.05.
Locations 1 2 3 4 5 6 7 8 9
1 . Bermuda 0
2. FL (Gulf) 0.127 0 3. Keys Adult -0.031 0.172 0 4. Keys Larvae -0.001 0.329* -0.030 0 5. Bahamas 0.594* 0.999* 0.530* 0.474* 0 6. Belize 0.635* 0.999* 0.561* 0.504* 0.023 0 7. St. Croix 0.694* 0.999* 0.640* 0.594* -0.032 0.002 0 8. Panama 0.632* 0.999* 0.571* 0.514* 0.017 -0.008 0.035 0 9. Venezuela 0.670* 0.999* 0.619* 0.571* -0.014 0.035 -0.009 0.053 0 10. N Brazil 0.354* 0.999* 0.253* 0.160* 0.664* 0.707* 0.589* 0.661* 0.621*
The two primary lineages sort geographically by latitude: one is subtropical (Gulf of Mexico, Florida Keys and Bermuda) the other predominantly tropical (the remaining locations, but also present in the Florida Keys and Bermuda). One of the shortest geographic distances between sampled populations (Bahamas - Gulf of Mexico, ca. 500 km) also represents one of the greatest genetic divergences (average number of corrected
pairwise differences 30.68; ®ST = 0.904).
Discussion
The two main lineages in H. bivittatus appear to be separated by an ecological rather than a dispersal barrier. The lineage present in the Gulf of Mexico, Florida Keys
and Bermuda (C and D in Figure 4-2) is restricted to subtropical waters, whereas the other lineage is mostly in tropical waters. The colder and sediment rich waters of the northern Gulf of Mexico are an unsuitable habitat for most wrasse species, and H. bivittatus is the only member of the genus that inhabits those waters. 43
Figure 4-2. Phylogenetic tree of all (107) Halichoeres bivittatus haplotypes. Geographical locations of haplotypes are: A. Brazil; B. Caribbean; C. Florida and Bermuda; D. Bermuda. Some examples of distance barriers (more than 1000 km), one ecological barrier (subtropical versus tropical reefs) and the Amazon barrier are indicated by dashed lines. Arrows indicate tropical haplotypes that were found in subtropical locations. Branch lengths are according to indicated scale; the branch leading to the outgroup (H radiatus) was reduced by 50%. 44
Further evidence that the Florida/Bermuda lineage is adapted to colder waters is its
relatively great phylogenetic depth at Bermuda. Bermuda is the northernmost outpost of
Atlantic tropical reef fauna, and is severely affected by glaciations (Smith-Vaniz et al.
1999). Most tropical species cannot survive in Bermuda during colder glacial periods, as
indicated by the low level of endemism (Briggs 1995). The monophyletic lineage of H.
bivittatus at Bermuda (D in Figure 4-2) indicates a population history that predates the
most recent interglacial interval. The additional “tropical” haplotypes present at the
Florida Keys and Bermuda, one or two mutations derived from haplotypes in tropical
samples (indicated by arrows in lineage B of Figure 4-2), seem to represent recent
colonizations, possibly following the last glacial maximum (20,000 YBP).
Since the two lineages co-occur at the Florida Keys and Bermuda, the only
explanation compatible with allopatric differentiation would be historical separation
followed by secondary contact, with the fast flowing waters of the Gulf Stream as a
dispersal barrier separating the Gulf of Mexico from the Caribbean. This explanation
would require a barrier that was stronger in the past and has recently become ineffective.
Evidence from fossil foraminifera accumulation at the bottom of the Florida Straits
indicates that the Gulf Stream was weaker during the last and possibly other glacial
maxima (Lynch-Stieglitz et al. 1999). Thus, since gene flow occurs during the present
interglacial period when the barrier is operating at full strength, it is unlikely that it effectively ceased migration between the Caribbean and Florida in the past.
Interestingly, neither the Amazon barrier nor the environmental differences between Brazil and the Caribbean (Chapter 2) seem to strongly influence the genetic structure of H. bivittatus. The explanation for this may lay in this species benthic 45
(post-larval) ecology. H. bivittatus is one of the most generalist Atlantic Halichoeres
with regards to habitat. It occupies inshore and offshore waters, being observed over
sand, rubble (Figure 4-1), sea grass, rocky or reef bottoms, whereas most other species in
the genus (excepting H. poeyi) inhabit reefs almost exclusively (Randall 1967). Because
of its broad habitat preferences, the environmental differences between coastal Brazil and
the Caribbean may not be a barrier for this species. The significant population structure
between Brazil and Caribbean locations (Table 4-2) may originate from weak effects of
distance or the Amazon, but the presence of “Brazilian” haplotypes in Venezuela and
Belize (lineage A in Figure 4-2), indicates that crossing of the Amazon is possible on a recent evolutionary timescale. CHAPTER 5 COLOR PATTERN VARIATION, AND THE PHYLOGEOGRAPHY OF FOUR SPECIES OF Halichoeres (LABRIDAE) IN THE WESTERN ATLANTIC
Introduction
Little is known about the evolutionary significance of bright color patterns in reef
fishes (McMillan et al. 1998). Sexual selection related to color appear to be present in
damselfishes (Pomacentridae, Thresher and Moyer 1983), but no correlation between
mating success and color pattern was observed in the blue-head wrasse (Labridae;
Warner and Schultz 1992). In closely related species, coloration has been proposed to be
useful in mate recognition. The sharpnose pufferfishes are an example of a group with
little or no diagnostic external morphological characters, where color has been proposed
as important in speciation (Allen and Randall 1977). Moreover, there is strong evidence of assortative mating based on color and ecological segregation among the color morphs of hamlets (Serranidae; Domeier 1994).
In reef fish taxonomy, color pattern is consistently used as a useful diagnostic character. When color differences appear in populations that also show slight morphological differences, than those populations are usually elevated to specific status
(Randall 1998). However, color alone is rarely used as a species defining character, especially in groups with highly variable color patterns like wrasses (Labridae).
Wrasses of the genus Halichoeres in the western Atlantic provide an excellent model system to examine the relationship between speciation and color change. The populations surveyed in this study are present on both sides of recognized biogeographic
46 47
barriers. Populations on either side of the barriers are considered the same species, but they show consistent color differences as follows:
• The juveniles of H. cyanocephalus in Brazil lack a blue spot on the mid-ventral portion of the soft dorsal fin present on juveniles of the Caribbean population (Figure 5-1).
• The terminal-phase males of H. garnoti at Bermuda have a red band on the upper posterior portion of the body, whereas males from the Caribbean have a black band at the same place (Figure 5-2).
• The upper body of individuals from the Brazilian populations of H. maculipinna is usually brownish pink, whereas individuals from the Caribbean have a yellowish green upper body (Figure 5-3).
The fourth species examined in this study is H. poeyi (Figure 5-4). It shows no
color difference between populations in Brazil and the Caribbean. However, it is subject
to the same biogeographic barriers as H. cyanocephalus and H. garnoti, and is herein used as a control.
Figure 5-1. Halichoeres cyanocephalus at northeastern Brazil (A, photo by Gerald Allen) and Dry Tortugas, Florida (B, photo by Paul Humann). The arrow on photo B indicates dark spot present only on the Caribbean population. 48
Figure 5-2. Halichoeres garnoti at Bermuda (A, photo by Luiz Rocha) and St. Lucia (B, photo by Paul Humann).
Figure 5-3. Halichoeres maculipinna at northeastern Brazil (A, photo by Bertran Feitoza) and the Bahamas (B, photo by Luiz Rocha).
Figure 5-4. Halichoeres poeyi in a turbid coralline algae reef off northeastern Brazil (Photo by Luiz Rocha). d
49
Methods and Materials
The species Halichoeres cyanocephalus, H. garnoti and H. maculipinna exhibit
color variation across their ranges and populations with different color patterns were
sampled. In addition, the widely distributed H. poeyi (a species that has no color
differences across its entire range) was sampled to serve as a control species. The fish
were collected with pole spears or hand nets while scuba diving or snorkeling in
Bermuda, the Bahamas, Florida Keys, Belize, St. Croix (USVI), Venezuela, coastal
Brazil (northeastern), and Trindade Island (Figure 3-1; Table 5-1).
The techniques and protocols used for tissue preservation, DNA isolation, PCR
amplification and purification, sequencing analysis, selection of model of evolution and
phylogenetic reconstruction were the same as those in Chapter 3. The Tamura-Nei model
(Tamura and Nei 1 983) with gamma distribution shape parameter of 0.01 was chosen.
Results
Halichoeres cyanocephalus
A 701 bp segment from the cytochrome b gene was analyzed from 17 individuals.
While sample sizes are low, Brazilian and Belizean populations are separated by at least
= 16 mutations (d 0.023) and the 0St between Brazil and Belize was 0.890. A total of
seven polymorphic sites distributed among four haplotypes were identified for the
Brazilian lineage, and seven polymorphic sites distributed among six haplotypes for the
Belizean lineage. Mean nucleotide frequencies in the Brazilian lineage were A=0.22,
C=0.30, G=0.17, T=0.31, and in the Belizean lineage A=0.22, C=0.31, G=0.16, T=0.31.
The transition - transversion ratio was 5.5. Pairwise distances within lineages ranged
from 1 . 1 7 to 2.83 nucleotide substitutions ( = 0.002 to 0.004). 50
The phylogenetic analysis (Figure 5-5) assigned the haplotypes of Halichoeres
cyanocephalus into two lineages (Brazil and Belize). No morphological difference was
detected between the lineages; however, a slight color difference is present (Figure 5-1).
Figure 5-5. Phylogenetic tree of all (9) Halichoeres cyanocephalus haplotypes. Geographical locations of haplotypes are color coded as follows: Brazil, black; Belize, gray. One ecological barrier (Brazilian versus Caribbean reefs)
is indicated by dashed lines. \ Branch lengths are according to indicated scale; the branch leading to the outgroup (H. radiatus) was reduced by 50%.
Halichoeres garnoti
A 704 bp segment from the cytochrome b gene was analyzed from 116 individuals.
A total of 66 polymorphic sites were distributed among 55 haplotypes. Mean nucleotide frequencies were A=0.22, C=0.30, G=0.16, T=0.32. The transition - transversion ratio
was 10.16 : 1. Genetic distances among populations ranged from 0.06 to 2.45 nucleotide
= substitutions ( d 0.001 to 0.004). Haplotype diversity was relatively high and overall nucleotide diversity (tt) was low in all populations (Table 5-1). No significant population structure was observed across the species’ entire range from Bermuda to Venezuela
(Table 5-2). 51
Table 5-1 . Sample size, number of haplotypes, haplotype diversity and nucleotide diversity of the populations surveyed. N Haplotypes h n
Halichoeres cyanocephalus Belize 12 6 0.68+0.15 0.00210.001 Brazil 5 4 0.90±0.16 0.00410.003 Total 17 10 Halichoeres garnoti Bahamas 21 17 0.9710.03 0.00810.005 Belize 21 15 0.9510.03 0.00910.005 Bermuda 27 20 0.9710.02 0.00810.004
Florida 3 1 0.0010.00 0.0010.00 St. Croix 23 18 0.9810.02 0.00910.005 Venezuela 22 16 0.9710.02 0.00910.005 Total 117 55 Halichoeres maculipinna Bahamas 19 12 0.9010.06 0.00310.002 Belize 19 12 0.8710.07 0.00210.001 Brazil 5 4 0.9010.16 0.00210.001 Florida 3 2 0.6710.31 0.00110.001 St. Croix 18 9 0.8010.09 0.00210.001 Trindade 5 3 0.7010.21 0.00110.001 Venezuela 17 11 0.8810.07 0.00310.002 Total 86 44 Halichoeres poeyi Belize 20 12 0.9310.03 0.00810.005 North Brazil 9 7 0.9410.07 0.00710.005 South Brazil 9 6 0.9210.07 0.00310.002 St. Croix 21 14 0.9010.06 0.00710.004 Total 59 31
Table 5-2. Population pairwise Ost for Halichoeres garnoti. No comparisons are significant at p=0,05.
Locations 1 2 3 4 5 6
1. Bermuda 0 2. Florida 0.001 0
3. Bahamas -0.023 0.041 0 4. Belize 0.011 -0.026 -0.004 0 5. St. Croix -0.006 0.141 -0.024 -0.005 0 6. Venezuela -0.013 -0.078 -0.016 0.018 -0.017 0 52
No geographic signal was detected in the phylogenetic analysis (Figure 5-6) of
Halichoeres garnoti. Individuals with a red dorsum (indicated by arrows in Figure 5-6) were nested within the larger Caribbean lineage.
Figure 5-6. Phylogenetic tree of all (55) Halichoeres garnoti haplotypes. No geographical signal was detected in the phylogeny. Arrows indicate haplotypes shared between Bermuda and one or more Caribbean location. Branch lengths are according to indicated scale; the branch leading to the
outgroup ( H poeyi) was reduced by 50%.
Halichoeres maculipinna
A 691 bp segment from the cytochrome b gene was analyzed from 86 individuals.
A total of 71 polymorphic sites distributed among 44 haplotypes were identified. Mean nucleotide frequencies were A=0.22, C=0.29, G=0.17, T=0.32. The transition - 53
transversion ratio was 5.91 : 1. Two lineages separated by 45.2 to 49.0 nucleotide substitutions (d = 0.065 to 0.071 sequence divergence) were observed. Genetic distances
within lineages ranged from 0.01 to 2.05 nucleotide substitutions (d = 0.001 to 0.003).
Haplotype diversity was relatively high and overall nucleotide diversity (n) was low in all populations of both lineages (Table 5-1).
The two lineages were allopatric, one northern (Florida, Bahamas, St. Croix, Belize and Venezuela) and the other southern (coastal Brazil and Trindade Island), being
separated by highly significant 0 Sx values (0St =0.958-0.984). No significant pairwise
0 St values were observed within either lineage (Table 5-4).
Table 5-3. Population pairwise Ost for Halichoeres maculipinna. Asterisks indicate significance at p=0.05.
Locations 1 2 3 4 5 6 7
1 . Florida 0
2. Bahamas -0.101 0
3. Belize -0.075 0.006 0
4. St. Croix -0.105 0.010 -0.014 0
5. Venezuela -0.100 -0.002 0.013 0.009 0 6. Coastal Brazil 0.973* 0.958* 0.969* 0.971* 0.959* 0 7. Trindade 0.984* 0.961* 0.972* 0.974* 0.963* 0.001 0
The phylogenetic analysis (Figure 5-7) assigned the haplotypes of Halichoeres maculipinna into two lineages (Brazil and the North Atlantic). No morphological
difference was detected between the lineages; however, a slight color difference is
present (Figure 5-3). It is also apparent from the tree in Figure 5-7 that nucleotide diversity was low in this species. 54
Distance — barrier A
Ecological barrier Amazon barrier rC
c
- Distance barrier c B € t c
c
F
/ / H. radiatus 0.005 substitutions/site
Figure 5-7. Phylogenetic tree of all (44) Halichoeres maculipinna haplotypes. Geographical locations of haplotypes are: A. coastal Brazil; B. Caribbean, the Bahamas and Florida. Some examples of distance barriers (more than 1000 km), one ecological barrier (turbid coastal Brazilian reefs versus clear water Caribbean and North Atlantic reefs) and the Amazon barrier are indicated by dashed lines. Branch lengths are according to indicated scale; the branch
leading to the . outgroup (H radiatus ) was reduced by 50%.
Halichoeres poeyi
A 702 bp segment from the cytochrome b gene was analyzed from 59 individuals.
A total of 40 polymorphic sites were distributed among 31 haplotypes. Mean nucleotide
frequencies were 1 A=0.2 1 , C=0.30, G=0. 6, T=0.32. The transition - transversion ratio 55
was 9.0 : 1 . An overall Ost of 0.203 was obtained, with the populations in coastal Brazil
(south of the Amazon) being significantly different from those from the Caribbean. No significant Ost values were observed within the Caribbean or Brazilian provinces (Table
5-4).
Table 5-4. Population pairwise Ost for Halichoeres poeyi. Asterisks indicate significance at p=0.05.
Locations 1 2 3 4
1. Belize 0
2. St. Croix 0.053 0
3. N Brazil 0.366* 0.222* 0 4. S Brazil 0.324* 0.174* -0.045 0
H. garnoti
Figure 5-8. Phylogenetic tree of all (31) Halichoeres poeyi haplotypes. Arrows indicate haplotypes shared between Brazil and one or more North Atlantic location. Branch lengths are according to indicated scale; the branch leading to the
outgroup (//. garnoti) was reduced by 50%. d
56
No geographic signal was detected in the phylogenetic analysis (Figure 5-8) of
Halichoeres poeyi. Individuals from Brazil (indicated by arrows in Figure 5-8) were nested within the Caribbean lineage.
Discussion
Halichoeres cyanocephalus
The genetic divergence ( = 2.3%) between the Brazilian and Caribbean populations of H. cyanocephalus (Figure 5-5) corresponds to a subtle but consistent color
difference (Figure 5-1). The genetic divergence observed within H. cyanocephalus is very similar in magnitude to that between H. brasiliensis and H. radiatus (d = 2.4%).
With only two populations surveyed, further sampling is necessary to ascertain the
location of, and to identify the mechanisms driving, the observed genetic differentiation.
The Amazon barrier is unlikely to be the site of differentiation, because H.
cyanocephalus occurs over deep sponge bottoms off Brazil (Rocha et al. 2000) and
French Guiana (Uyeno et al. 1983), the latter under the Amazon plume. Individuals in
Belize, Florida and the Virgin Islands have the color pattern showed on Figure 5-1 B, whereas individuals in north and south Brazil have the pattern shown in Figure 5-1 A.
Thus, it is likely that the lineages represent distinct species previously undetected.
Halichoeres garnoti
As noted by Smith-Vaniz et al. (1999), there are noticeable color differences
between Caribbean and Bermuda populations of this species (Figure 5-2). The color
differences in the species pair Halichoeres radiatus and H. brasiliensis and in the
Brazilian and Caribbean populations of H. cyanocephalus and H. maculipinna correspond
to diagnostic genetic differences in cytochrome b\ however this is not true for H. garnoti. 57
Two hypothesis may explain the absence of genetic differentiation despite the presence of color differences:
• The population at Bermuda is exposed to some environmental condition that causes their color to change phenotypically without an underlying genetic basis.
• The population at Bermuda is young, possibly post-dating the last glacial maximum, such that color differences that appeared as a result of rapid selection (or
drift) are not accompanied by fixed genetic differences at the cytochrome b.
The first hypothesis remains untested, however there is evidence favoring the second. During the last glacial maximum (25,000 to 15,000 yr B.P.) temperatures at
Bermuda were 3 to 5°C lower than today (Sachs and Lehman 1 999), bringing mean annual temperatures below the 21°C (with much lower temperatures during the winter) threshold necessary for reef coral survival, and leading to the likely extermination of
most of the reef fish fauna (Smith-Vaniz et al. 1 999). In the absence of natural selection
(present environmental conditions at Bermuda are very similar to those at Caribbean
islands), fixed genetic differences would accumulate on average after Ne generations,
where Ne is the effective number of locally breeding adults (Slatkin 1985; 1987).
Assuming that H. garnoti is a strictly tropical species (it does not occur at the
northern Gulf of Mexico or in any coastal American location north of Florida), it is
probable that the Bermuda population is less than 1 5,000 years old. Random drift requires a relatively small effective population size and very low rates of migration between the Caribbean and Bermuda to allow genetic divergence that are detectable in
this gene in such a short period. H. garnoti is one of the most common wrasses at
Bermuda, and it is not unusual to see more than 20 adult individuals in small patch reefs,
thus the effective population size of H. garnoti at Bermuda (at least on a contemporary
scale) is relatively large. Moreover, vast tropical fish mortality, associated with very low 58
th temperatures (7.2°C) was reported in the beginning of the 20 century in Bermuda
(Smith-Vaniz et al. 1999). Thus, it is possible that insufficient time has passed for random drift to produce noticeable genetic differences between the Bermuda and
Caribbean populations. Color differences may have a genetic basis, but if they originated recently, the difference will not be detected in neutral genes due to insufficient time for lineage sorting.
Indications that H. garnoti recently arrived in Bermuda (Figure 2-9) seem to contradict the apparent persistence of H. bivittatus at that location. However, the deep
lineage of H. bivittatus observed in Bermuda (lineage D in Figure 2-2) is related to the apparently cold-water resistant lineage at the Gulf of Mexico. Colder temperatures during glaciation may have been sufficient to extirpate tropical taxa (including H. garnoti), but not the temperate-adapted H. bivittatus lineage.
Halichoeres maculipinna
The pelagic larval duration of H. maculipinna (30 days; Sponaugle and Cowen
1997) is the longest among the Atlantic Halichoeres. Surprisingly, this species showed the deepest genetic divergence observed in this study (d = 6.5%) between Brazilian and
Caribbean populations, demonstrating the poor value of PLD as a predictor of genetic divergence. Despite the deep genetic split between Brazil and the Caribbean, careful examination of several individuals of H. maculipinna from locations at the two regions revealed no morphological differences. However, slight differences in coloration were detected (Figure 5-3).
The divergence observed between the northern and southern lineages of H.
maculipinna is the highest among all species examined. Two possible (and not mutually
exclusive) explanations are that this divergence is a result of 1) the additive effects of an 59
ecological and a dispersal barrier and 2) a higher degree of habitat specialization. There
is no field survey data that indicates that H. maculipinna crosses the Amazon barrier, it is a shallow water species (20 -30 m max depth; Humann and Deloach 2002; Randall and
Bohlke 1965), and has never been collected under the Amazon (Collette and Riitzler
1977) or in deep sponge bottoms off northeastern Brazil (Rocha et al. 2000), thus the
Amazon appears to be an effective barrier due to strict habitat preferences. Isolation by the Amazon outflow, augmented by environmental differences between Brazil and the
Caribbean (or coincident placement of an ecological and a dispersal barrier as illustrated
in Figure 5-7) apparently generates a high sequence divergence (d = 6.5%) relative to H. radiatus / brasiliensis (d= 2.4%) and H. cyanocephalus (d = 2.3%).
The second explanation invokes the feeding ecology of this species. H. maculipinna has the weakest jaw musculature, the smallest mouth gap and the most specialized diet (fewer and smaller species of benthic invertebrates compared to congeners) among all Atlantic Halichoeres (Randall 1967; Wainwright 1988). As a specialized predator, H. maculipinna may be more sensitive to habitat differences than the other more generalist species surveyed here. In this case, stronger natural selection may lead to earlier and faster differentiation, possibly generating the higher observed divergences in this species.
Halichoeres poeyi
This was the only Halichoeres present on both sides of the Amazon that showed no phylogenetic partitions (Figure 5-8). Similarly to H. bivittatus (which also does not seem to be affected by the Amazon or the environmental differences between Brazil and the
Caribbean), H. poeyi showed only a population-level difference between Brazil and the
Caribbean. These two species share some key ecological traits: they are the most 60
generalist Atlantic Halichoeres in regards to habitat, occurring in inshore and offshore waters, over sand, rubble, sea grass, rocky or reef bottoms (Figure 5-4), whereas most other species inhabit exclusively reefs (Randall 1967). Thus, this generalist may not be limited by environmental differences that may coincide with phylogenetic differentiation in other (more specialist) species of the genus. The significant population structure
between Brazil and Caribbean locations (Table 5-4) is probably caused by weak effects of the Amazon.
Conclusion
There is inconsistency between color differences and genetic partitions in two of the three the species surveyed. The color differences within H. cyanocephalus and H. maculipinna correspond to deep genetic partitions at the cytochrome b gene. However,
genetic similarity at this same gene is observed between populations of H. garnoti with striking color differences. Thus, caution against the utilization of color differences (or the lack thereof) in the systematics of wrasses is herein suggested. A similar conclusion was reached by McMillan et al. (1999) for butterflyfishes (Chaetodontidae). CHAPTER 6 GENERAL CONCLUSIONS
Contrary to expectations of congruent population structure due to similar dispersal
potential, the efficacy of barriers varied among species of Atlantic Halichoeres. Deeply-
divergent genetic lineages were observed within the traditional limits of all species but H.
garnoti and H. poeyi. The former was the only species that did not show significant
population genetic structure in any part of its range. Most species that occur on both
sides of the Amazon are composed of two deeply divergent lineages, one in coastal Brazil
and the other in the Caribbean, North Atlantic and, in one case, Brazilian oceanic islands.
In contrast, H. bivittatus and H. poeyi although showing some population structure across
the Amazon barrier, show little or no genetic divergence there. However H. bivittatus
does have two deeply divergent lineages, one restricted to northern sub-tropical waters
and the other widely distributed, mostly in the tropics and extending south to Brazil.
Most species analyzed in this study showed evidence for effective long distance dispersal, as indicated by the lack of significant population subdivision among locations separated by vast geographical distances of unsuitable habitat (either open ocean waters or the area influenced by the Amazon). Of the four deep and two shallow divergences documented, three deep and one shallow fall at major transitions in habitat that do not coincide with dispersal barriers. The remaining two shallow ones fall at the Amazon outflow, thus at a location that is both major transition and habitat, and a dispersal barrier by virtue of unsuitable habitat along a long stretch of shore. Thus, putative dispersal barriers do not provide reasonable explanation to the observed pattern, but ecological
61 62
differences, for the adult (benthic) stage, do. Below I review the evidence in support of this hypothesis, species-by-species.
Reconciling Local Adaptation with the Pelagic Larval Stage
The pelagic larval stage present in all Halichoeres represents a powerful force
against local adaptation through effective migration, mainly because it counteracts the effects of natural selection by promoting the fixation of alleles with the best average
fitness across all subpopulations, even if this allele is not the best in some areas
(Lenormand 2002). Ecological speciation is being proposed in Chapters 3, 4 and 5 as an important mechanism of diversification in coral reef fishes, but how can this mechanism work in the presence of long distance dispersal and potentially strong migration?
In reef fishes (and probably other marine organisms) larval retention, or the ability to remain close to the natal site during the larval stage, may offer an explanation.
Evidence for larval retention has come from several studies that draw upon varied methodologies, such as analysis of otolith microchemistry, mark and recapture,
endemism and larval distributions (for a review see Swearer et al. 2002). Moreover, a myriad of biological (Kingsford et al. 2002; Leis and McCormick 2002) and oceanographic (Cowen 2002) mechanisms that would allow larvae to remain near their natal sites were proposed.
One of the immediate consequences of larval retention is the reduction (not complete elimination) of migration between distant locations. By reducing migration, self-recruitment would indirectly favor local adaptation. However, local adaptation (or
local random differentiation) will only proceed if natural selection (or genetic drift) is operating. Genetic drift is a slow process by which mutations that originate in any given population are either fixed or lost by chance. Under genetic drift, roughly one successful 63
migrant per generation will prevent differentiation of populations. Natural selection acts
upon the same variation as drift, but it can quickly drive an allele to fixation (or
extinction) if its relative fitness in a given environment is high (or low) (Hedrick 2000).
In the absence of larval retention, high migration rates would promote the fixation
of alleles with the best average fitness across all subpopulations, regardless of local
optima, and prevent ecological speciation. However, larval retention favors local
adaptation by reducing migration. Thus, with larval retention (or lower population
connectivity in an evolutionary time scale), both genetic drift and natural selection can
operate at a local scale, and ecological speciation is possible.
Conclusions
Significant population or species level genetic partitions were observed in all
species that have their range separated by the Amazon outflow. However, recent or
ongoing but limited crossing of the barrier is evident in all species but H. maculipinna,
which is the one that shows the deepest genetic divergence between Brazil and the
Caribbean. The two species that have the broadest habitat tolerance in the genus H poeyi ( .
and H. bivittatus), show population-level partitions, rather than phylogenetic structure,
between sample locations in the turbid reefs off Brazil and clear reefs in the Caribbean.
This indicates that different environmental conditions between the two regions separated
by the Amazon may be more important in driving the observed divergences than the
barrier per se. Moreover, a phylogenetic break that also seems to be driven by different environmental conditions (tropical versus subtropical), rather then dispersal barriers was observed within H. bivittatus.
There is inconsistency between color differences and genetic partitions in Atlantic
Halichoeres. The color differences within H. cyanocephalus, H. maculipinna and the pair 64
H. radiatus and H. brasiliensis correspond to deep genetic partitions at the cytochrome b.
However, genetic similarity at this same gene is observed between populations of H.
garnoti with striking color differences. Moreover, the deep genetic divergence between
tropical and subtropical lineages of H. bivittatus is apparently not accompanied by
matching color differences. Thus, caution against the utilization of color differences (or
the lack thereof) in the systematics of wrasses is here in suggested. A similar conclusion
was reached by McMillan et al. (1999) for butterflyfishes (Chaetodontidae).
Genetic divergences ranged from 2.5 to 6.5% in lineages apparently separated by
the Amazon. A conventional molecular of 2% per million years for the cytochrome b
gene (Avise 2000) suggests that this divergence is between 1.25 to 3.25 my old, much
younger than the estimated age of the initial connection of the Amazon with the Atlantic
(10 my B.P., Chapter 1). Thus dispersal from one area to the other after the formation of
the Amazon, followed by genetic differentiation due to divergent natural selection or
isolation seems to be a more plausible explanation for the observed divergence than
vicariance.
The observed distribution of genetic partitions shows that gene flow exists between
environmentally similar, but geographically distant locations. In this scenario it is highly
likely that migration occurs between geographically close locations, however divergent
selection pressures may overcome the effects of migration (which is small because of self-recruitment), resulting in ecological partitions and possibly ecological speciation.
The pattern drawn from this study indicates that divergent environmental conditions can be as important as (or sometimes more important than) vast distances of unsuitable habitat (either open ocean waters or the area influenced by the Amazon) in producing 65
genetic partitions, and that benthic-stage habitat preferences may be strongly influencing the biogeography of western Atlantic reef fishes. LIST OF REFERENCES
Allen, G. R., and J. E. Randall. 1977. Review of the sharpnose pufferfishes (Subfamily Canthigasterinae) of the Indo-Pacific. Rec. Aust. Mus. 30:475-517.
Allison, M. A., M. T. Lee, A. S. Ogston, and R. C. Aller. 2000. Origin of Amazon mudbanks along the northeastern coast of South America. Mar. Geol. 163:241-256.
Amos, B., and A. R. Hoelzel. 1991. Long-term preservation of whale skin from DNA analysis. Rep. Int. Whal. Comm. Spec. Iss. 13:99-103.
Avise, J. C. 1992. Molecular population structure and the biogeographic history of a regional fauna: a case history with lessons for conservation biology. Oikos 63:62- 76.
Avise, J. C. 2000. Phylogeography: the history and formation of species. Harvard University Press, Cambridge.
Barton, N. H. 1988. Speciation. Pp. 185-218 in A. A. Myers and P. S. Giller, eds. Analytical Biogeography: an integrated approach to the study of animal and plant distributions. Chapman and Hall, New York.
Bellwood, D. R., and P. C. Wainwright. 2002. The History and Biogeography of Fishes on Coral Reefs. Pp. 5-32 in P. F. Sale, ed. Coral Reef Fishes. Dynamics and Diversity on a Complex Ecosystem. Academic Press, New York.
Bierne, N., F. Bonhomme, and P. David. 2003. Habitat preference and the marine- speciation paradox. Proc. R. Soc. Lond. B 270:1399-1406.
Bowen, B. W., A. L. Bass, L. A. Rocha, W. S. Grant, and D. R. Robertson. 2001. Phylogeography of the trumpetfish (Aulostomus spp.): ring species complex on a global scale. Evolution 55:1029-1039.
Briggs, J. C. 1974a. Marine Zoogeography. McGraw-Hill, New York.
Briggs, J. C. 1974b. Operation of zoogeographic barriers. Syst. Zool. 23:248-256.
Briggs, J. C. 1987. Antitropical distribution and evolution in the Indo-West Pacific Ocean. Syst. Zool. 36:237-247.
Briggs, J. C. 1995. Global biogeography. Elsevier, New York.
Briggs, J. C. 1999. Modes of speciation: marine Indo-West Pacific. Bull. Mar. Sci. 65:645-656.
66 67
Brown, J. H., and M. V. Lomolino. 1998. Biogeography. Sinauer Associates, Inc., Sunderland, MA.
Carvalho-Filho, A. 1999. Peixes: costa brasileira. MarcaD'Agua, Sao Paulo.
Chaves, H. A. F. 1979. Projeto REMAC: Geotnorfologia da margem continental brasileira e areas oceanicas adjacentes. Serie Projeto REMAC, Rio de Janeiro.
Collette, B. B., and K. Riitzler. 1977. Reef fishes over sponge bottoms off the mouth of the Amazon River. Proc. 3rd Int. Coral Reef Symp. 1:305-310.
Collin, P. 1975. The Neon Gobies. TFH Publications, Inc., Neptune City, NJ.
Cowen, R. K. 2002. Larval dispersal and retention, and consequences for population connectivity. Pp. 149-170 in P. F. Sale, ed. Coral Reef Fishes. Dynamics and Diversity in a Complex Ecosystem. Academic Press, New York.
Cox, C. B., and P. D. Moore. 2000. Biogeography: an ecological and evolutionary approach. Blackwell Science, Oxford.
Curtin, T. B. 1 986. Physical observations in the plume region of the Amazon River during peak discharge -II. Water masses. Cont. Shelf Res. 6:53-71.
Curtin, T. B., and R. V. Legeckis. 1986. Physical observations in the plume region of the
Amazon River during peak discharge - 1. Surface variability. Cont. Shelf Res. 6:31- 51.
da Silveira, I. C. A., W. S. Brown, and G. R. Flierl. 2000. Dynamics of the North Brazil Current retroflection region from the Western Tropical Atlantic Experiment
observations. J. Geophys. Res. 105:28,559-28,583.
Degens, E. T., S. Kempe, and J. E. Richey. 1991. Summary: biogeochemistry of major
world rivers. Pp. 323-347 in E. T. Degens, S. Kempe and J. E. Richey, eds. Biogeochemistry of Major World Rivers. Wiley, New York.
Dobzhansky, T. 1937. Genetics and the Origin of Species. Columbia University Press, New York.
Domeier, M. L. 1994. Speciation in the serranid fish Hypoplectrus . Bull. Mar. Sci. 54:103-141.
Edwards, A., and R. Lubbock. 1983. Marine Zoogeography of St Paul's Rocks. J. Biogeogr. 10:65-72.
Emery, A. R. 1973. Atlantic bicolor damselfish (Pomacentridae): a taxonomic question. Copeia 1973:590-594. 68
Excoffier, L., P. E. Smouse, and J. M. Quatro. 1992. Analysis of molecular variance inferred from metric distances among DNA haplotypes: application to human mitochondrial DNA restriction data. Genetics 131:479-491.
Feitoza, B. M. 1999. Composicao da ictiofauna recifal do talude continental da Paraiba. Pp. 79. Departamento de Zoologia. Universidade Federal da Paraiba, Joao Pessoa.
Figueiredo, J. L., and N. A. Menezes. 1980. Manual de peixes marinhos do sudeste do Brasil. University of Sao Paulo, Sao Paulo.
Filchak, K. E., J. B. Roethele, and J. L. Feder. 2000. Natural selection and sympatric divergence in the apple maggot Rhagoletis pomonella. Nature 407:739-742.
Floeter, S. R., and J. L. Gasparini. 2000. The southwestern Atlantic reef fish fauna:
composition and zoogeographic patterns. J. Fish Biol. 56:1099-1 1 14.
Floeter, S. R., and J. L. Gasparini. 2001. Brazilian endemic reef fishes. Coral Reefs 19:292.
Floeter, S. R., R. Z. P. Guimaraes, L. A. Rocha, C. E. L. Ferreira, C. A. Rangel, and J. L.
Gasparini. 2001 . Geographic variation in reef-fish assemblages along the Brazilian coast. Global Ecol. Biogeogr. 10:423-432.
Gasparini, J. L., and S. R. Floeter. 2001. The shore fishes of Trindade Island, western
South Atlantic. J. Nat. Hist. 35:1639-1656.
Gasparini, J. L., L. A. Rocha, and S. R. Floeter. 2001. A new Ptereleotris (TELEOSTEI:
MICRODESMIDAE) from the Brazilian coast, aqua, J. Ichthyol. Aquat. Biol. 4:109-114.
Gates, D. M. 1993. Climate change and its biological consequences. Sinauer Associates, Inc., Sunderland, MA.
Gilbert, C. R. 1972. Characteristics of the Western Atlantic Reef-fish Fauna. Quart. J. Florida Acad. Sci. 35:130-144.
Gilbert, C. R. 1977. Status of the western South Atlantic apogonid fish Apogon americanus, with remarks on other Brazilian species. Copeia 1977:25-32.
Gold, J. R., and L. R. Richardson. 1998. Mitochondrial DNA diversification and the
population structure in fishes from the Gulf of Mexico and western Atlantic. J. Hered. 89:404-414.
Greenfield, D. W. 1 988. A review of the Lythrypnus mowbray complex (Pisces: Gobiidae), with the description of a new species. Copeia 1988:460-470. 69
Greenfield, D. W., and L. P. Woods. 1974. Eupomacentrus diencaeus Jordan and Rutter, a valid species of damselfish from the western tropical Atlantic. Fieldiana (Zool.) 65:9-20.
Hedrick, P. W. 2000. Genetics of Populations. Jones and Bartlett, Sudbury, MA.
Heiser, J. B., R. L. Moura, and D. R. Robertson. 2000. Two new species of Creole
Wrasse (Labridae: Clepticus ) from opposite sides of the Atlantic, aqua, J. Ichthyol. Aquat. Biol. 4:67-76.
Helfman, G. S., B. B. Collette, and D. E. Facey. 1997. The Diversity of Fishes. Blackwell Science, Inc., Malden, MA.
Hoorn, C. 1994. An environmental reconstruction of the palaeo-Amazon River system (Middle-Late Miocene, NW Amazonia). Palaeogeogr. Palaeoclimatol. Palaeoecol. 112:187-238.
Hoorn, C. 1996. Miocene deposits in the Amazonian foreland basin. Science 273:122.
Hoorn, C., J. Guerrero, G. A. Sarmiento, and M. A. Lorente. 1995. Andean tectonics as a cause for changing patterns in Miocene northern South America. Geology 23:237- 240.
Humann, P., and N. Deloach. 2002. Reef Fish Identification. New World Publications, Jacksonville.
Humphries, C. J., P. Y. Ladiges, M. Roos, and M. Zandee. 1988. Cladistic biogeography. Pp. 371-404 in A. A. Myers and P. S. Giller, eds. Analytical Biogeography: an integrated approach to the study of animal and plant distributions. Chapman and Hall, New York.
Johns, G. C., and J. C. Avise. 1998. A comparative summary of genetic distances in vertebrates from the mitochondrial cytochrome b gene. Mol. Biol. Evol. 15:1481- 1490.
Jones, G. P., M. J. Milicich, M. J. Emslie, and C. Lunow. 1999. Self-recruitment in a coral reef fish population. Nature 402:802-804.
Joyeux, J. C., S. R. Floeter, C. E. L. Ferreira, and J. L. Gasparini. 2001. Biogeography of
tropical reef fishes: the South Atlantic puzzle. J. Biogeogr. 28:831-841.
Kingsford, M. J., J. M. Leis, A. Shanks, K. C. Lindeman, S. G. Morgan, and J. Pineda. 2002. Sensory environments, larval abilities and local self-recruitment. Bull. Mar. Sci. 70:309-340.
Knowlton, N. 2000. Molecular genetic analyses of species boundaries in the sea. Hydrobiologia 420:73-90. 70
Kuehl, S. A., D. J. DeMaster, and C. A. Nittrouer. 1986. Nature of sediment accumulation on the Amazon continental shelf. Cont. Shelf Res. 6:209-225.
Lacson, J. M., and D. C. Morizot. 1991. Temporal genetic variation in subpopulations of bicolor damselfish {Stegastes partitus) inhabiting coral reefs in the Florida Keys
Mar. Biol. 1 10:353-357.
Leao, Z. M. A. N. 1986. Guia para identificacao dos corais do Brasil. Universidade Federal da Bahia, Salvador, Brasil.
Leao, Z. M. A. N., and J. M. L. Dominguez. 2000. Tropical coast of Brazil. Mar Poll Bull. 41:112-122.
Leis, J. M., and M. I. McCormick. 2002. The Biology, Behavior, and Ecology of the Pelagic Larval Stage of Coral Reef Fishes. Pp. 171-199 in P. F. Sale, ed. Coral Reef Fishes. Dynamics and Diversity on a Complex Ecosystem. Academic Press New York.
Lenormand, T. 2002. Gene flow and the limits to natural selection. Trends Ecol Evol 17:183-189.
Lentz, S. J. 1995. The Amazon River plume during AMASSEDS: subtidal current
variability and the importance of wind forcing. J. Geophys. Res. 100:2377-2390.
Li, G., and D. Hedgecock. 1998. Genetic heterogeneity, detected by PCR-SSCP, among samples of larval Pacific oysters ( Crassostrea gigas) supports the hypothesis of large variance in reproductive success. Can. J. Fish. Aquat. Sci. 55:1025-1033.
Lieske, E, and R. Myers. 1994. Coral Reef Fishes. Harper-Collins, London.
Lopez, M. 2001. Architecture and depositional pattern of the Quaternary deep-sea fan of the Amazon. Mar. Petrol. Geol. 18:479-486.
Lubbock, R., and A. Edwards. 1981. The fishes of Saint Paul's Rocks. J. Fish Biol 18:135-157.
Lynch-Stieglitz, J„ W. B. Curry, and N. Slowey. 1999. Weaker Gulf Stream in the Florida Straits during the las glacial maximum. Nature 402:644-648.
Mallet, J. 2001. The speciation revolution. J. Evol. Biol. 14:887-888.
Masson, S., P. and Delecluse. 2001 . Influence of the Amazon River runoff on the tropical Atlantic. Phys. Chem. Earth (B) 26:137-142.
Mayr, E. 1942. Systematics and the Origin of Species. Columbia University Press
Mayr, E. 1947. Ecological Factors in Speciation. Evolution 1:263-288. 71
Mayr, E. 1982. Processes of speciation in animals. Pp. 1-19 in C. Barigozzi, ed. Mechanisms of Speciation. Liss, New York.
McCafferty, S. S., E. Bermingham, B. Quenquille, S. Planes, G. Hoelzer, and K. Asoh. 2002. Historical biogeography and molecular systematics of the Indo-Pacific genus Dascyllus (Teleostei: Pomacentridae). Mol. Ecol. 1 1:1377-1392.
McMillan, W. O., L. A. Weigt, and S. R. Palumbi. 1999. Color pattern evolution, assortative mating, and genetic differentiation in brightly colored butterflyfishes (Chaetodontidae). Evolution 53:247-260.
Melson, W. G., S. R. Hart, and G. Thompson. 1972. St Paul's Rocks, equatorial Atlantic; petrogenesis, radiometric ages, and implications on sea-floor spreading. Mem. Geol. Soc. Am. 132:241-272.
Menezes, N. A., and J. L. Figueiredo. 1985. Manual de peixes marinhos do sudeste do Brasil. University of Sao Paulo, Sao Paulo.
Meyer, A. 1993. Evolution of mitochondrial DNA in fishes. Pp. 1-38 in P. W. Hochanchka and T. P. Mommsen, eds. Biochemistry and molecular biology of fishes. Elsevier, New York.
Milliman, J. D., and R. H. Meade. 1983. World-wide delivery of river sediment to the oceans. J. Geol. 91:1-21.
Mitton, J. B. 1997. Selection in Natural Populations. Oxford University, New York.
Mora, C., and P. F. Sale. 2002. Are populations of coral reef fish open or closed? Trends Ecol. Evol. 17:422-428.
Moura, R. J. L., L. Figueiredo, and 1. Sazima. 2001. A new parrotfish (Scaridae) from Brazil, and revalidation of Sparisoma amplum (Ranzani, 1842), Sparisoma frondosum (Agassiz, 1831), Sparisoma axillare (Steindachner, 1878) and Scarus trispinosus Valenciennes, 1840. Bull. Mar. Sci. 68:505-524.
Muss, A., D. R. Robertson, C. A. Stepien, P. Wirtz, and B. W. Bowen. 2001. Phylogeography of Ophioblennius: the role of ocean currents and geography in reef fish evolution. Evolution 55:561-572.
Nei, M. 1987. Molecular Evolutionary Genetics. Columbia University Press, New York.
Nittrouer, C. A., and D. J. DeMaster. 1986. Sedimentary processes on the Amazon continental shelf: past, present and future research. Cont. Shelf Res. 6:5-30.
Ormond, R. F. G., and C. M. Roberts. 1997. The biodiversity of coral reef fishes. Pp. 216-257 in R. F. G. Ormond, J. D. Gage and M. V. Angel, eds. Marine Biodiversity: patterns and processes. Cambridge University Press, Cambridge. 72
Palumbi, S. R. 1992. Marine speciation on a small planet. Trends Ecol. Evol. 7:114-118.
Parenti, P., and J. E. Randall. 2000. An annotated checklist of the species of the labroid fish families Labridae and Scaridae. Ichthyol. Bull. J. L. B. Smith Inst. Ichthyol 68:1-97.
Paulay, G. 1997. Diversity and distribution of reef organisms. Pp. 298-353 in C. E. Birkeland, ed. Life and death on coral reefs. Chapman & Hall, New York.
Paulay, G., and C. Meyer. 2003. Diversification in the tropical Pacific: comparisons between marine and terrestrial systems and the importance of founder speciation. Integr. Comp. Biol. 42:922-934.
Peterson, R. G., and L. Stramma. 1991. Upper-level circulation in the South Atlantic Ocean. Prog. Oceanogr. 26:1-73.
Planes, S. 2002. Biogeography and larval dispersal inferred from population genetic analysis. Pp. 201-220 in P. F. Sale, ed. Coral Reef Fishes. Dynamics and Diversity on a Complex Ecosystem. Academic Press, New York.
Posada, D., and K. A. Crandall. 1998. Model Test: testing the model of DNA substitution. Bioinformatics 14:817-818.
Potter, P. E. 1997. The Mesozoic and Cenozoic paleodrainage of South America: a natural history. J. S. Amer. Earth Sci. 10:331-344.
Ramos, R. T. C. 1994. Analise da composi 9ao e distribuipao da fauna de peixes demersais da plataforma continental da Paraiba e Estados vizinhos. Revta Nordest Biol. 9:1-30.
Ramos, R. T. C., C. R. Rocha, and L. A. Rocha. 2003. New species of Emblemaria (Teleostei: Chaenopsidae) from Northern Brazil. Copeia 2003:95-98.
Randall, J. E. 1967. Food habits of reef fishes of the West Indies. Stud. Trop. Oceanogr. Miami 5:665-847.
Randall, J. E. 1996. Caribbean Reef Fishes. TFH Publications, Neptune City, NJ.
Randall, J. E. 1998. Zoogeography of shore fishes of the Indo-Pacific region. Zool Studies 37:227-268.
Randall, J. E., G. R. Allen, and R. C. Steene. 1997. Fishes of the Great Barrier Reef and Coral Sea. University of Hawaii, Honolulu, HI.
Randall, J. E., and J. E. Bohlke. 1965. Review of the Atlantic labrid fishes of the genus
Halichoeres. Proc. Acad. Nat. Sci. Phila. 1 17:235-259. 73
Randall, J. E., and P. S. Lobel. 2003. Halichoeres socialis : a new labrid fish from Belize. Copeia 2003:124-130.
Rivalenti, G., M. Mazzucchelli, V. A. V. Girardi, R. Vannucci, M. A. Berbieri, A. Zanetti, and S. L. Goldstein. 2000. Composition and processes of the mantle lithosphere in northeastern Brazil and Fernando de Noronha: evidence form mantle xenoliths. Contr. Mineral Petrol. 138:308-325.
Robertson, D. R. 2001. Population maintenance among tropical reef fishes: Inferences from small-island endemics. Proc. Natl. Acad. Sci. USA 98:5667-5670.
Robins, C. R. 1971. Distributional patterns of fishes from coastal and shelf waters of the tropical western Atlantic. Pp. 249-255. Symposium on investigations and resources of the Caribbean Sea and adjacent regions. FAO, Fisheries Report 71-2, Rome.
Rocha, L. A. 2002. Brazilian Reef Fishes. Pp. 462-479 in P. Humann and N. Deloach, eds. Reef Fish Identification: Florida, Caribbean, Bahamas. New World Publications, Jacksonville.
Rocha, L. A., A. L. Bass, D. R. Robertson, and B. W. Bowen. 2002. Adult habitat preferences, larval dispersal, and the comparative phylogeography of three Atlantic surgeonfishes (Teleostei: Acanthuridae). Mol. Ecol. 11:243-252.
Rocha, L. A., R. Z. P. Guimaraes, and J. L. Gasparini. 2001. Redescription of the Brazilian wrasse Thalassoma noronhanum (Boulenger, 1890) (Teleostei: Labridae). aqua, J. Ichthyol. Aquat. Biol. 4:105-108.
Rocha, L. A., and I. L. Rosa. 1999. New species of Haemulon (Teleostei: Haemulidae) from the northeastern Brazilian coast. Copeia 1999:447-452.
Rocha, L. A., and I. L. Rosa. 2001a. Baseline assessment of reef fish assemblages of
Parcel Manuel Luiz Marine State Park, Maranhao, north-east Brazil. J. Fish Biol. 58:985-998.
Rocha, L. A., and R. S. Rosa. 2001b. Halichoeres brasiliensis (Bloch, 1791), a valid wrasse species (Teleostei: Labridae) from Brazil, with notes on the Caribbean
species Halichoeres radiatus (Linnaeus, 1758). aqua, J. Ichthyol. Aquat. Biol 4:161-166.
Rocha, L. A., I. L. Rosa, and B. M. Feitoza. 2000. Sponge-dwelling fishes of northeastern Brazil. Env. Biol. Fishes 59:453-458.
Rocha, L. A., I. L. Rosa, and R. S. Rosa. 1998. Peixes recifais da costa da Paraiba, Brasil. Revta. Bras. Zool. 15:553-566.
Rosa, R. S., C. R. Nunes, and L. A. Rocha, in press. Diversidade da ictiofauna do nordeste brasileiro: uma compilacao das especies de teleosteos marinhos costeiros. Revta. Nordest. Biol. 74
Rosa, R. S., I. L. Rosa, and L. A. Rocha. 1997. Diversidade da ictiofauna de pofas de mare da praia do Cabo Branco, Joao Pessoa, Paraiba, Brasil. Revta. Bras Zool 14:201-212.
Sachs, J. P., and S. J. Lehman. 1999. Subtropical North Atlantic temperatures 60,000 to 30,000 years ago. Science 286:756-759.
Sarver, S. K., J. D. Silberman, and P. J. Walsh. 1998. Mitochondrial DNA sequence evidence supporting the recognition of two subspecies of the Florida spiny lobster Panulirus argus. J. Crust. Biol. 18:177-186.
Sazima, I., J. L. Gasparini, and R. L. Moura. 1998. Gramma brasiliensis, a new basslet
from the western South Atlantic (Perciformes: Grammatidae). aqua, J. Ichthyol. Aquat. Biol. 3:39-43.
Sazima, I., and R. L. Moura. 2000. Shark (Charcharhinus perezi), cleaned by the goby (Elacatinus randalli), at Fernando de Noronha Archipelago, western South Atlantic. Copeia 2000:297-299.
Schluter, D. 2001. Ecology and the origin of species. Trends Ecol. Evol. 16:372-380.
Schneider, S., D. Roessli, and L. Excoffier. 2000. ARLEQUIN, Version 2.0: a Software for Population Genetics Data Analysis. Genetics and Biometry Laboratory, University of Geneva, Switzerland.
Shulman, M. J., and E. Bermingham. 1995. Early life histories, ocean currents and the population genetics of Caribbean reef fishes. Evolution 49:1041-1061.
Slatkin, M. 1985. Gene flow in natural populations. Annu. Rev. Ecol. Syst. 16:393-430.
Slatkin, M. 1987. Gene flow and the geographic structure of natural populations. Science 236:787-792.
Smith, C. L. 1997. National Audubon Society field guide to tropical marine fishes of the Caribbean, the Gulf of Mexico, Florida, the Bahamas and Bermuda. Alfred A. Knopf, New York.
Smith-Vaniz, W. F., B. B. Collette, and B. E. Luckhurst. 1999. Fishes of Bermuda: History, zoogeography, annotated checklist, and identification keys. Allen Press Inc., Lawrence, Kansas.
Sponaugle, S., and R. K. Cowen. 1997. Early life history traits and recruitment patterns of Caribbean wrasses (Labridae). Ecol. Monogr. 67:177-202.
Swearer, S. E., J. E. Caselle, D. W. Lea, and R. R. Warner. 1999. Larval-retention and recruitment in an island population of a coral-reef fish. Nature 402:199-802. 75
Swearer, S. E, J. S. Shima, M. E. Hellberg, S. R. Thorrold, G. P. Jones, D. R. Robertson, S. G. Morgan, K. A. Selkoe, G. M. Ruiz, and R. R. Warner. 2002. Evidence of self- recruitment in demersal marine populations. Bull. Mar. Sci. 70:251-271.
Swofford, D. L. 2002. Phylogenetic Analysis Using Parsimony (*and other Methods). Version 4.0bl0. Sinauer, Sunderland, MA.
Szpilman, M. 2000. Peixes marinhos do Brasil. Guia pratico de identificacao. Aqualung, Rio de Janeiro.
Tamura, K., and M. Nei. 1983. Estimating the number of nucleotide substitutions in the control region of mitochondrial DNA in humans and chimpanzees. Mol. Biol Evol 15:512-526.
Thresher, R. E., and J. T. Moyer. 1983. Male success, courtship complexity, and patterns of sexual selection in three congeneric species of sexually monochromatic and dichromatic damselfishes (Pisces: Pomacentridae). Anim. Behav. 31:1 13-127.
Tringali, M. D., T. M. Bert, S. Seyoum, E. Bermingham, and D. Bartolacci. 1999. Molecular phylogenetics and ecological diversification of the transisthmian fish genus Centropomus (Perciformes: Centropomidae). Mol. Phylogenet. Evol 13193- 207.
Uyeno, T., K. Matsuura, and E. Fujii. 1983. Fishes trawled off Suriname and French Guiana. Japan Marine Fishery Resource Research Center, Tokyo.
Vermeij, G. J. 1978. Biogeography and adaptation: Patterns of marine life. Harvard University Press, Cambridge, MA.
Veron, J. E. 1995. Corals in space and time: biogeography and evolution of the Scleractinia. Cornell University Press, Ithaca, NY.
Via, S. 2001 . Sympatric speciation in animals: the ugly duckling grows up. Trends Ecol. Evol. 16:325-413.
Victor, B., and G. M. Wellington. 2000. Endemism and the pelagic larval durantion of reef fishes in the eastern Pacific Ocean. Mar. Ecol. Prog. Ser. 205:241-248.
Wainwright, P. C. 1988. Morphology and ecology: functional basis of feeding constraints in Caribbean labrid fishes. Ecology 69:635-645.
Warner, R. R., and E. T. Schultz. 1992. Sexual selection and male characteristics in the
blueheaded wrasse, Thalassoma bifasciatunv. mating site acquisition, mating site defense, and female choice. Evolution 46:1421-1442.
Wellington, G. M., and D. R. Robertson. 2001. Variation in larval life-history traits among reef fishes across the Isthmus of Panama. Mar. Biol. 138:1 1-22. 76
Williams, J. T., and A. M. Smart. 1983. Redescription of the Brazilian labrisomid fish Starksia brasiliensis. Proc. Biol. Soc. Wash. 96:638-644. BIOGRAPHICAL SKETCH
I was born in in 1973 Joao Pessoa, northeastern Brazil. During a biology class in
middle school, I decided that I wanted to be a biologist. My interest in fishes also came at
an early age. When I was 14, 1 was snorkeling to collect and keeping saltwater fishes in
aquaria. few later, A years I started my bachelor’s degree in biological sciences at the
Universidade Federal da Paralba, from which I graduated in early 1997. That same year I entered their graduate program in Zoology. In 1999, 1 completed my master’s thesis on the reef fishes of Parcel Manuel Luiz, an isolated reef formation off the Northern
Brazilian coast.
Undaunted by curiosity, I decided to pursue an academic career and began studying the phylogeography of Atlantic reef fishes at the University of Florida in the fall of 1999.
I will continue studying several aspects of reef fish biogeography, population genetics, evolution and systematics through a postdoctoral position at the Smithsonian Tropical
Research Institute, Panama.
77 I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy.
Debra Murie, Chair Assistant Professor of Fisheries and Aquatic Sciences
I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy.
Gustav Paulay, Cochair Assistant Curator of the Florida Museum of Natural History
I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy.
Carter R. Gilbert Courtesy Professo^ of Zoology
I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a
dissertation for the degree of Doctor of Philosophy. , AATiUrfU, Colette M. St. Mary Assistant Professor of Zoology
I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy.
William F. Smith-Vaniz Research Marine Biologist, United States Geological Survey, Biological Resources Division, Florida Caribbean Science Center, Gainesville, Florida I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy.
A. K~X Stephen A. Karl Associate Professor of Biology, University of South Florida, Tampa, Florida
This dissertation was submitted to the Graduate Faculty of the College of Agricultural and Life Sciences and to the Graduate School and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosophy.
August 2003 SL Dean, College of Agricultural ark Sciences
Dean, Graduate School