EXTREME PHENOTYPIC VARIATION AMONG CRYPTIC CARIDEAN SHRIMP FROM SAN SALVADOR ISLAND, BAHAMAS.
Robert E. Ditter1, Anna M. Goebel2 and Robert B. Erdman2
1Department of Marine and Ecological Sciences 2Department of Biological Sciences Florida Gulf Coast University Ft. Myers, FL 33965
ABSTRACT the dissolution of the underlying carbonate plat- form (Edwards, 1996; Mylroie and Carew, 2003). Extensive phenotypic variation is docu- No study has successfully traced the lakes’ connec- mented in specimens of cryptic cave shrimp col- tion to the surrounding ocean on San Sal. Our lected on San Salvador Island, Bahamas in June of original objective was to compare species compo- 2012. Sixty two of the 70 individuals exhibited sition of cryptic caridean shrimp inhabiting the such immense variation, including characters not conduit mouths of anchialine pools and use this previously described to Barbouria cubensis, Bar- information to infer connections between lakes and bouria yanezi, Parhippolyte sterreri, or any mem- the surrounding ocean. ber of the family Barbouriidae, that identification using a traditional morphological approach proved impossible. Examples of such characters include terminal eyestalk spines, gross spination of the tel- son and the presence of sensory dorsal organs on the carapace. The source and extent of morpholog- ical variation in these shrimp remains unclear, but may be due to environmental or genetic causes, or a combination of both. We note that rampant vari- ation is observed in taxonomically important char- acters that were previously considered highly con- served and therefore were used to discriminate among species of shrimp. If these characters are highly variable then the taxonomic identity of shrimp in this group may need to be reconsidered.
INTRODUCTION
A common feature among many tropical islands in the Caribbean is the presence of seem- ingly disjointed tidal lakes and ponds. San Salva- dor (San Sal) is a small island in the Bahamian ar- chipelago and nearly half of its land mass is cov- Figure 1. Map of San Salvador Island labeled with ered by anchialine pools that range from brackish sites sampled in 2012; (1) Shrimp Holes, (2) Oys- to hypersaline in nature (Mylroie and Carew, ter Pond, (3) Wild Dilly Pond, (4) Fortune Hill 2003). Subsurface tidal flows permit marine con- Plantation Pond, (5) Mermaid Pond, (6) Watlings ditions to exist in many of the landlocked pools via Blue Hole and (7) Blue Hole #5 (a.k.a. Double seawater exchange through conduits created from Decker Blue Hole).
1 The 15th Symposium on the Natural History of the Bahamas
It is not unusual for multiple species of hibited by specimens collected from anchialine cryptic carideans to be found inhabiting the same pools on San Sal. lake on other Caribbean islands (Wicksten, 1996; De Grave et al., 2009). Because these shrimp have METHODS planktonic larvae, inhabit conduits with tidal flow, and occur in multiple lakes, these shrimp are excel- Specimen Collection lent candidates to examine possible interconnectiv- ity among lakes (Manning and Hart, 1984; Boho- During June 2012, 70 shrimp were collect- nak, 1999). ed from seven anchialine ponds and blue holes on In order to infer connections using anchi- San Sal (Figure 1). Samples were collected with aline shrimp, the species composition of shrimp on hand nets or by baited minnow traps. Shrimp were the island must first be identified. Only one spe- transported to the Gerace Research Center (GRC) cies (Barbouria cubensis) has been previously rec- and maintained in running seawater until preserva- orded from San Sal (Hobbs, 1978). During 2011, tion. All specimens were preserved in 95-100% another species (Parhippolyte sterreri) was col- ETOH and transported to Florida Gulf Coast Uni- lected from Mermaid Pond (Ditter and Erdman, versity (FGCU). personal observations). Both, P. sterreri and B. cubensis are listed as critically endangered on the Morphological Identification IUCN Red List (Iliffe, 1996). A second species of Barbouria (B. yanezi) that is thought to be synon- We examined 13 morphological characters ymous with B. cubensis (De Grave, Bauer and (Figure 2) commonly used to discriminate between Felder, personal communication with Ditter) was members of the family Barbouriidae (Chace and described from Cozumel, Mexico in 2008 (Mejía et Manning, 1972; Hobbs, 1978; Hart and Manning, al., 2008) and is thought to occur only on the Yu- 1981; Manning and Hart, 1984; Wicksten, 1996; catan Peninsula. Meíja et al., 2008) using a Leica compound dis- Typically, decapods can be identified based secting microscope equipped with a Lumenera IN- on morphology. We assumed we would be able to FINITYx camera. INFINITY Analysis software identify species using morphology and would re- was used to capture images and take measurements quire DNA to identify only unusual cases. How- of morphological characters. Morphological char- ever, we found such extensive phenotypic variation acters that would require dissection were not ex- among specimens, species level identifications amined to prevent damage to specimens (e.g. max- based on traditional methods proved impossible. illipeds or the appendix masculina). Therefore, the objective of this study became doc- umenting the extreme morphological variation ex- Figure 2. Morphological characters examined: (1) cornea width relative to eyestalk width; (2) rostrum length relative to antennular peduncle, (3) number of pre- and post-orbital dorsal and (4) ventral spines on rostrum; (5) terminal shape of telson, (6) number of dorsal and (7) terminal telson spines; (8) scaphocerite length to width ratio; (9) carapace spines, (10) carapace texture and sensory dorsal organs; (11) shape and (12) spines of plerua of the 4th & 5th pleomere; (13) 1st & 2nd pereiopods chelate.
2 The 15th Symposium on the Natural History of the Bahamas
0
2 2 (1)
0 0 (0)
1 1 (0)
Range
malformed
spines absent
chelae present
both unarmed or
unassignable shape
4th & 5th low angle
2.7x 2.7x as long as wide
anterior presentSDO
terminal spine present
MinimumObserved
cornea greatly reduced,
smooth with only single
not reaching past eyestalk
antennal & branchiostegal
antennal
rd
8
15 15 (7)
13 13 (3)
13 13 (8)
Range
present
segment
both armed
chelae present
extra antennal & 4th & 5th rounded
separated by expected features for for separated by features expected
3.5x 3.5x as long as wide branchiostegal spine
reaching 3
dorsal organs present
terminal spine present
(1 (1 wider & 1 narrower)
MaximumObserved
not smooth with 4 sensory
cornea width assymertrical
nd nd
4-5
6 6 (3) 4 4 (2)
Barbouriidae spp. Barbouriidae
pointed
3-4 (1-2) 3-4
Typical Typical
mentioned
chelae present
spines present
3x as long as wide
antennal segment
barely reaching 2
4th & 5th acute angle
cornea wider than stalk
4th unarmed 5th armed
Parhippolyte sterreri Parhippolyte
carapace smooth, no SDO antennal & branchiostegal
Numbering in Character column corresponds to Figure column 2 Legend. corresponds inNumbering Character
1-7
6 6 (3)
4 4 (2)
5-6 (3-4) 5-6
Typical Typical
rounded
mentioned
chelae present
spines present
antennal segment
nd
2.9x 2.9x as long as wide
2
4th & 5th acute angle
Barbouria cubensis Barbouria
4th unarmed 5th armed
does not extend beyond
carapace smooth, no SDO
antennal & branchiostegal
cornea narrower than stalk
Characters used to discriminate between Barbouriidae species discriminatebetween Barbouriidae to used Characters Characters common between members of the familyBarbouriidae the betweenmembers of common Characters
and the range of observed variation. range and the
spines
,
chelate
5th 5th pleura
5th 5th pleura
Characters
telson(pairs)
eyestalk width
presense of SDO
on telsonon (pairs)
antennal peduncle antennal
(8) (8) length vs. width
spines (postorbital)
(10) only (10) &antennal
(9) carapace texture, (9) carapace and
(13) 1st and 2nd periopods 1st(13) 2nd and
(12) armorment (12) of 4th and
(1) cornea width reative(1) cornea to
(6) (6) number of dorsal spines
(5) (5) terminal shape of telson
(3) (3) number of dorsal rostrum
(2) (2) rostrum length relative to
(11) relative(11) shape of 4th and
branchiostegal spinesbranchiostegal present
(7) (7) number of distal spines on (4) (4) number of ventral rostrum
P. sterreri
and
ommon morphological characters used to used discriminate morphological among characters ommon
C
Pereiopods
Pleura
Carapace
Scaphocerite
Telson
Rostrum Eyes Structure
Table 1. B. cubensis 3 The 15th Symposium on the Natural History of the Bahamas
al
observed abnormal phenotypes; Top Row: phenotypes;observed abnormal Top
compared to examples of tocompared examples
P. sterreri
and
B. cubensis B.
xpected phenotypes for for phenotypes xpected
Figure 3. E length, of and rostrum Row: on telson, termin number Bottom Middle on rostrum spines spines and pairing Row: of number dorsal and terminal spines of shape telson. 4 The 15th Symposium on the Natural History of the Bahamas
RESULTS Eyes
Based on 13 morphological characters Just over 34% of specimens had eyes that (Table 1), only six shrimp were identified as Bar- varied from the description of the eyes of B. cu- bouria cubensis and two were identified as bensis. All specimens had some form of pigment- Parhippolyte sterreri. The species identity of the ed eyes. The cornea width of most individuals was remaining 62 shrimp could not be positively iden- typically narrower than the eyestalk, but 24 indi- tified based on morphological characters due to viduals had cornea that were equal to or larger immense phenotypic variation (Figure 3). The than the width of the eyestalk, had malformed variation exhibited by these shrimp often fell out- cornea, were asymmetrical in width or the cornea side of characters prescribed to either genus (Bar- was greatly reduced and a single terminal spine bouria or Parhippolyte). Extreme variation was was present on the eyestalk (Figure 4). common among all lakes with no discernable dis- tribution pattern.
Figure 4. Example of asymmetry in right and left cornea and eyestalk morphology; a) right lateral cor- nea severely reduced and eyestalk with terminal spine present (indicated by arrows), b) dorsal view of eyes, c) left lateral cornea narrower than eyestalk width, eyestalk spine absent.
Rostrum Telson
Nearly 74% of individuals had rostrums Based on the prescribed characters, 67% that did not match the prescribed character states of individuals could not be assigned as matching for B. cubensis or P. sterreri. The number of ros- the telson of B. cubensis or P. sterreri. The shape tral spines exhibited greater variation then has of the posterior margin of the telson was highly been previously recorded (Table 1). The rostrum variable; 24 specimens were described as having a did typically reach the second article of the anten- rounded posterior margin, 24 were described as nular peduncle. Twenty one specimens had ros- have a pointed posterior margin and the remaining trums reaching the middle of the second article, 22 were intermediate in shape and could not be while 22 specimens had rostrums reaching, or just assigned. The number telson spines and terminal reaching the second article and five specimens shape exhibited the greatest range of variation had rostrums reaching or nearly reaching the third among morphological characters (table 1). article. Sixteen specimens had rostrums not reaching past the first article and the remaining Carapace six had rostrums that were either broken or not nearly reaching the distal edge of the second Only 13% of specimens had carapace penduncular segment. spines that did not match that of B. cubensis and
5 The 15th Symposium on the Natural History of the Bahamas
P. sterreri. Sixty one specimens had antennal and scribed as being shared by the three species (i.e. branchiostegal spines, while nine individuals were terminal shape of telson or rostrum length). Addi- missing one or more spines that did not appear to tionally, some specimens exhibited morphological be the result of breakage. The carapace of most characters not present in any shrimp within the specimens was smooth with the exception of family Barbouriidae (Figures 3 and 5). This sug- small sensory dorsal organs (SDO) situated along gests that some characters which were considered the medial line of the cephalothorax (Figure 5). to be highly conserved in taxonomic classification The anterior SDO was found associated with the of caridean shrimp actually may not be conserved. distal postorbital rostral spine and posterior SDOs If these characters are variable within and among were found within the cardiac notch (Lerosey- multiple species then the classification of other Aubril and Meyer, 2013). species, based on these characters, should be reexamined. Other characters found to be highly varia- ble include; the number of spines on the appendix masculina of the 2nd pleopod, spination of the ex- opod of the uropod, carapace shape and the pres- ence of SDOs on the dorsal margin of the telson. Documentation of variation in these characters is in progress. The spination of appendix masculina is the most important of the unreported characters as it may be the key to discriminating between species in the presence of so much other variation, and may lead to synonymizing B. cubensis and B. yanezi (Karge et al., 2013). The source of variation in these shrimp is Figure 5. Representative examples of posterior unclear and examples of phenotypic variation are sensory dorsal organ present on the post-dorsal abundant in the animal kingdom. This variation margin of the cephalothorax from two specimens. may be due to inherent phenotypic plasticity (DeWiit et al., 2000; Brian et al., 2006; Lardies Pleura of the Abdominal Somites and Bozinovic, 2008) although extensive pheno- typic plasticity has not been previously reported in In the majority of specimens the pleura of these shrimp. Other possible non-genetic based the third and fourth somites were unarmed (with- sources of extensive variation could be due to out posterolateral tooth), whereas the fifth and physical trauma during early development or dur- sixth were armed (with posterolateral tooth). In ing molting (Giménez, 2006, Vogt et al., 2008), some instances only the sixth somite was armed damage due to parasitic infection (Goodman and or the presence of spines was asymmetrical. Ad- Johnson, 2011), or environmental factors such as ditionally, the shape of the 4th and 5th pleura was salinity and temperature (Ituarte et al., 2007; Re- highly variable and could most often be described uschel and Schubart, 2007). If the source of var- as acute. However, it was not uncommon for the iation has a non-genetic basis, then further study shape of the 4th pleura to be described as obtuse or will be required to identify the source and impli- round. cations for the conservation of these species in the Caribbean. DISCUSSION Alternately, the source of variation may have a genetic basis, such as severe inbreeding Many of the shrimp examined in this study (Creasey et al., 2000; Fumagalli et al., 2002), the exhibited characters synonymous with P. sterreri, presence of hybrid swarms (Wolf and Mort, 1986; B. cubensis or B. yanezi, and that are not de- Perry et al., 2002), incipient speciation (Dawson,
6 The 15th Symposium on the Natural History of the Bahamas
2005; Malay and Pauley, 2009), cryptic speciation ACKNOWLEDGMENTS (Steinauer et al., 2007), or sympatric speciation (Turner et al., 2008). If the source of variation is We would like to thank Dr. Donald T. due to severe inbreeding, then management efforts Gerace, Chief Executive Officer, and Tom Roth- may be required to restore genetic diversity to fus, Executive Director of the Gerace Research these critically endangered populations. If the Center, San Salvador, Bahamas. We’d like to variation is due to factors associated with specia- thank Dr. Ray Bauer for confirming the identifica- tion, then it is likely a result of isolation or intense tion of the initial specimen of Parhippolyte sterre- predation. If speciation is related to isolation, it ri. Special thanks go to Courtney Bennett and Gi- may be possible to infer geologic timelines using na Hendrick for their help in the field. Drs. Greg genetic information. Furthermore, if speciation is Tolley, Mike Parsons, Randy Cross, Matt Palm- a result of predation, it will be necessary to gain a tag, and Nora Demers provided valuable com- better understanding of interactions among anchi- ments and assistance. This research was funded in aline organisms. part by a student research award to RED from the In order to accurately identify these Gerace Research Center. Additional support was shrimp and identify the source of variation the use provided by the Whitaker Center and the Office of of molecular tools will be required. As these are Research and Sponsored Programs at Florida Gulf critically endangered due to their unique cryptic Coast University. Last but not least, we’d like to habitats (Manning and Hart, 1984; IUCN, 2012), thank the Ditter family and the Wayne family for a nondestructive tissue sampling technique was their encouragement and support. developed using the common pink shrimp Farfan- tepenaeus duorarum as a model organism (Ditter REFERENCES et al., 2013). If the extreme variation observed here has Brian, J.V., T. Fernandes, R.J. Ladle and P.A. a genetic basis, then taxonomic revisions will be Todd. 2006. Patterns of morphological and necessary. The phenotypic variation observed in genetic variability in UK populations of these shrimp may be enough to support the recon- the shore crab, Carcinus maenas Linnaeus, sideration of the taxonomic classification of the 1758 (Crustacea: Decapoda: Brachyura). genus Barbouria as being monophyletic. Addi- Journal of Experimental Marine Biology tionally, these shrimp may represent previously and Ecology. 329:47-54. unrecorded species. We anticipate that further molecular and morphological studies will identify Bohonak, A.J. 1999. Dispersal, Gene Flow, and the underlying cause of variation which may be Population Structure. The Quarterly Re- due to a complex combination of genetic and non- view of Biology. Vol. 74(1):21-45. genetic sources. Although we had hoped to identify the Chace, F.A., Jr., and R.B. Manning. 1972. Two species and their distribution among the suppos- new caridean shrimps, one representing a edly connected lakes on San Sal, we were not able new family, from marine pools on Ascen- to do so with confidence in most cases. Instead sion Island (Crustacea: Decopoda: Natan- we found abundant morphological variation. We tia). Smithsonian Contributions to Zoolo- plan to proceed with the two (possibly three) gy. 131:18 pp. known species that could be identified with mor- phology, and concurrently use a combined molec- ular and morphological approach to identity any new species and the role that isolation and gene flow through interconnected lakes may have played in their speciation.
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Creasey, S., A. Rogers, P. Tyler, J. Gage and D. Fumagalli, L., A. Snoj, D. Jesenšek, F. Balloux, Jollivet. 2000. Genetic and morphometric T. Jug, O. Duron, F. Brossier, A.J. Crivelli camparisons of squat lobster, Munidopsis and P. Berrebi. 2002. Extreme genetic dif- scobina (Decapoda: Anomura: Gala- ferentiation among the remnant popula- theidae) populations, with notes on the tions of marble trout (Salmo marmoratus) phylogeny of the genus Munidopsis. Deep- in Slovenia. Molecular Ecology. 11:2711- Sea Research II. 47:87-118. 2716.
Dawson, M.N. 2005. Incipient speciation of Cato- Giménez, L. 2006. Phenotypic links in complex stylus mosaicus (Scyphozoa, Rhizostome- life cycles: conclusions from studies with ae, Catostylidae), comparative phylogeog- decapod crustaceans. Integrative and raphy and biogeography in south-east Aus- Comparative Biology. 46(5):615-622. tralia. Journal of Biogeography. 32:55- 533. Goodman, B.A. and P.T.J. Johnson. 2011. Disease De Grave, S., N.D. Pentcheff, S.T. Ahyong, T.Y. and the extended phenotype: parasites con- Chan, K.A. Crandall, P.C. Dworschak, trol host performance and survival through D.L. Felder, R.M. Feldmann, C.H.J.M induced changes in body plan. PLoS ONE. Fransen, L.Y.D. Goulding, R. Lemaitre, 6(5):e20193. M.E.Y. Low, J.W. Martin, P.K.L. Ng, C.E. doi:10.1371/journal.pone.002093 Schweitzer, S.H. Tan, D. Tshudy and T. Wetzer. 2009. A classification of living Hart, C.W., Jr. and R.B. Manning. 1981. The cav- and fossil genera of decapod crustaceans. ernicolous caridean shrimp of Bermuda Raffles Bulletin of Zoology. 21:1-109 (Alpheidae, Hippolytidae, and Atyidae). Journal of Crustacean Biology. 1(3): 441- DeWitt, T.J., B.W. Robinson and D.S. Wilson. 456. 2000. Functional diversity among preda- tors of a freshwater snail imposes an adap- Hobbs, H.H., III. 1978. The Female of Barbouria tive trade-off for shell morphology. Evolu- cubensis (von Martens) (Decapoda: Hip- tionary Ecology Research. 2:129-148. polytidae) with Notes on a Population in the Bahamas. Crustaceana. 35(1):99-102. Ditter, R.E., R.B. Erdman, and A.M. Goebel. De- velopment of a nondestructive tissue sam- Iliffe, T.M. 1996. Barbouria cubensis and pling method for Decapod Crustaceans: A Somersiella sterreri. In: IUCN 2013. case study with the pink Shrimp Farfan- IUCN Red List of Threatened Species. tepenaeus duorarum. Presented at the 15th Version 2013.2.
8 The 15th Symposium on the Natural History of the Bahamas
Lardies, M.A. and F. Bozinovic. 2008. Genetic Steinauer, M.L., B.B. Nickol and G. Orti. variation for plasticity in physiological and 2007.Cryptic speciation and patterns of life-history traits among populations of an phenotypic variation of a highly variable invasive species, the terrestrial isopod acanthocephalan parasite. Molecular Ecol- Porcellio laevis. Evolutionary Ecology ogy. 16:4097-4109. Research. 10:747-762. Turner, B.J., D.D. Duvernell, T.M. Bunt and M.G. Lerosey-Aubril, R. and R. Meyer. 2013. The sen- Barton. 2008. Reproductive isolation sory dorsal organs of crustaceans. Biologi- among endemic pupfishes (Cyprinodon) cal Reviews. 88:406-426. on San Salvador Island, Bahamas: mi- crosatellite evidence. Biological Journal of Manning, R.B. and C.W. Hart, Jr. 1984. The Sta- the Linnean Society. 95:566-582. tus of the Hippolytid Shrimp Genera Bar- bouria and Ligur (Crustacea: Decapoda): Vogt, G., M. Huber, M. Thiemann, G. van den A Reevaluation. Proceedings of the Bio- Boogaart, O.J. Schmitz and C.D. Schubart. logical Society of Washington. 97(3):655- Production of different phenotypes from 665. the same genotype in the same environ- ment by developmental variation. The Malay, M.C.D. and G. Paulay. 2009. Peripatric Journal of Experimental Biology. 211:510- speciation drives diversification and dis- 513. tributional pattern of reef hermit crabs (Decapoda: Diogenidae: Calcinus). Evo- Wicksten, M.K. 1996. Parhippolyte cavernicola, lution. 64(3):634-662. new species (Decapoda: Caridea: Hip- polytidae) from the tropical eastern Pacif- Mejía, L.M., E. Zarza and M. López. 2008. Bar- ic, with taxonomic remarks on the genera bouria yanezi sp. Now., a new species of Somersiella and Koror. Journal of Crusta- cave shrimp (Decapoda, Barbouriidae) cean Biology. 16:201-207. from Cozumel Island, Mexico. Crusta- ceana. 81(6):663-672. Wolf, H.G. and M.A. Mort. 1986. Inter-specific hybridization underlies phenotypic varia- Mylroie, J.E. and J.L. Carew. 2003. Karst devel- bility in Daphnia populations. Oecologia. opment of carbonate islands. AAPG 68(4):507-511. Memoir 63. Pp. 54-76.
Perry, W.L., J.L. Feder and D.M. Lodge. 2001. Implications of hybridization between in- troduced and resident Orconectes crayfish. Conservation Biology. 15(6):1656-1666.
Reuschel, S. and C.D. Schubart. 2007. Con- trasting genetic diversity with phenotypic diversity in coloration and size in Xantho peressa (Brachyura: Xanthidae), with new results on its ecology. Marine Ecology. 28:1-10.
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