1999. The Journal of Arachnology 27:71±78

AN ADAPTIVE RADIATION OF HAWAIIAN : BIOGEOGRAPHIC AND GENETIC EVIDENCE

Jessica E. Garb: Zoology Department, University of at Manoa, Honolulu, Hawaii 96822

ABSTRACT. The Hawaiian Thomisidae are noted for being extremely species rich, as well as diverse in morphology and ecology. This exceptional diversity led early systematists to place the species into several genera with cosmopolitan distributions. It has been recently suggested that these species compose a single large adaptive radiation. Species-area relationships for all thomisid species and for F.O. Pickard-Cambridge 1900 (Thomisidae) species for various island areas were generated. Further, a phylogenetic hypothesis was constructed based on genetic distances between the Hawaiian thomisids and various outgroups using a 450 bp region of the mitochondrial cytochrome oxidase I (COI) gene to test for close genetic relationships. Despite the extraordinary isolation of the Hawaiian islands, the numbers of Misumenops and total thomisid species were found to be signi®cantly higher than predicted for an island system of its size. Phylogenetic analysis of COI suggests the Hawaiian thomisids are more closely related to each other than to representatives of genera to which they have been previously assigned. These results support the existence of a Hawaiian thomisid adaptive radiation, and merit further investigation using comparative methods.

The biota of the Hawaiian archipelago is due to its extreme isolation (Howarth & Mull characterized by a number of large species ra- 1992). However, the islands are exceptionally diations. These radiations result from the ex- diverse at the species level, due to extensive treme geographic isolation and topographical autochthonous speciation. The diversity of diversity of the islands (Carson & Clague Hawaiian closely follows this pattern. 1995). Natural colonization of the archipelago Of the 105 known families (Cod- has been largely limited to organisms having dington & Levi 1991), only 10 occur naturally exceptional dispersal capabilities, and those in the Hawaiian Islands, and many of these species that were sucessful colonizers experi- are represented by a single (Simon enced total genetic isolation from their source 1900; Suman 1964). Some of these genera populations. Founders that made the long have undergone extensive speciation (Gilles- journey frequently underwent rapid evolution pie et al. 1998). In particular, native species due to drift and selection in extremely small of the genera Tetragnatha Latreille 1831 (Te- populations (Carson 1994). The Hawaiian Is- tragnathidae), Argyrodes Simon 1864 and lands themselves are volcanic, formed at a Theridon Walckenaer 1805 (Therididae), Mis- ``hot spot'' connected to the Earth's core. As umenops F.O. Pickard-Cambridge 1900 the Paci®c tectonic plate continually rolls (Thomisidae), Sandalodes Keyserling 1883 northwestward over the hot spot, new islands (Salticidae) and Cyclosa Menge 1866 (Ara- are formed. Consequently, they are arranged neidae) are known to be unusually diverse and in chronological order. After initial coloniza- most, if not all, are endemic to the Hawaiian tion of the archipelago, it appears that taxa Islands (Table 1). It is likely that many more have frequently progressed down the island species within these groups remain to be dis- chain in a step-wise manner, resulting in re- covered. However, because many species have peated founder events as each new island is extremely small ranges of endemism, rapid colonized (Wagner & Funk 1995). This degradation of natural areas along with in- unique combination of biogeographical events creasing numbers of alien species, make these may explain some of the unusual aspects of spiders exceptionally vulnerable to extinction the composition of the Hawaiian biota. For (Gillespie & Reimer 1993). example, Hawaii's terrestrial biota is consid- The family Thomisidae attracted attention ered depauperate at higher taxonomic levels early in the study of Hawaiian biology. R.C.L.

71 72 THE JOURNAL OF ARACHNOLOGY

Table 1.ÐSpecies radiations of Hawaiian spiders.

% Native Considered Family Genus species endemic Reference Tetragnathidae Tetragnatha Ͼ52 100 Gillespie et al. (1998) Therididae Theridion Ͼ13 100 Simon (1900) Therididae Argyrodes Ͼ30 100 Gillespie et al. (1998) Thomisidae Misumenops 17 100 Suman (1970) Araenidae Cyclosa Ͼ7 100 Simon (1900) Salticidae Sandalodes Ͼ9 88 Simon (1900)

Perkins, a pioneering Hawaiian naturalist and one in which extensive adaptive morphologi- collector for the Fauna Hawaiiensis spent lit- cal evolution has played a signi®cant role. Ex- tle time in the pursuit of spiders. However, he amples of explosive adaptive radiations in is- recognized that ``the Thomisidae are probably land archipelagos illustrate how closely the most interesting and important group in related species often display great morpholog- the Hawaiian spiders'' (Perkins 1913). His ical diversity (Grant & Grant 1989). This phe- collections were examined by Eugene Simon nomenon is well documented in other Hawai- (1900), who described 14 new species and a ian spiders (Gillespie 1994; Gillespie et al. new genus of Thomisidae. These 14 species 1997), and other Hawaiian taxa (Roderick & were placed in the cosmopolitan genera Mis- Gillespie 1998). Consequently, if the Hawai- umena Latreille 1804, Thorell 1869 and ian thomisids constitute an adaptive radiation, Synaema Fabricius 1775 as well as the new they may represent another exceptional op- endemic genus Simon 1900. In a portunity for understanding evolutionary and subsequent revision of Hawaiian Thomisidae, ecological mechanisms that generate rapid di- Suman (1970) noted that the genitalia of the versi®cation. Hawaiian Diaea was extremely similar to that In this study I examine the species richness of the Hawaiian and these two gen- of Hawaiian thomisids in a biogeographical era were likely the same. Further, examination framework. Classical biogeographical theory of the setation and eyes of Hawaiian spiders (MacArthur & Wilson 1967) states that island previously assigned to Diaea and Misumena species diversity is a balance between immi- revealed that they were actually more similar gration and extinction. What determines the to representatives of Misumenops, a cosmo- rate of immigration and extinction depends politan genus, than to other representatives of largely on the size of an island and its distance Diaea and Misumena. Accordingly, represen- from a source. In this context one would pre- tatives of Diaea and Misumena were placed dict that the isolation and small size of Hawaii in Misumenops. Suman considered the endem- would result in a species poor fauna. Here I ic Mecaphesa to be related to the genus Ozyp- examine the species-area relationship for Ha- tila Simon 1964, and further suggested that waiian thomisids at the family and generic that all of the Hawaiian thomisids were likely levels in comparison to other island areas. derived from three separate colonizers, one Also, I conduct a phylogenetic analysis of Ha- that gave rise to the Hawaiian Misumenops, waiian thomisid species and representatives of one that gave rise to the endemic genus Me- the genera to which they have been assigned caphesa, and one that gave rise to the Ha- historically, in order to provide corroborative waiian Synaema (Suman 1970). Suman's re- evidence for a within-archipelago radiation. vision also resulted in the recognition of several new species, for a total of 21 described METHODS species, 17 of which are in the genus Misu- Biogeographical analysis.ÐA species-area menops. curve was generated for both total thomisid Recently, Lehtinen (1993) has suggested species and for species in the genus Misumen- that all Hawaiian thomisids comprise an adap- ops. Data for the distribution of thomisids and tive radiation generated from a single founder, Misumenops species have been assessed in GARBÐEVIDENCE FOR A HAWAIIAN THOMISIDAE RADIATION 73

Table 2.ÐSpecies used in sampling of a 450 bp region of mitochondrial cytochrome oxidase I.

Species Collection locality Misumenops anguliventris Simon 1900 Kauai, Oahu, Maui, Hawaii Island Misumenops cavatus Suman 1970 Hawaii Misumenops discretus Suman 1970 Kauai Misumenops editus Suman 1970 Oahu Misumenops facundus Suman 1970 Hawaii Island Misumenops insulanus Keyserling 1890 Oahu Misumenops imbricatus Suman 1970 Oahu, Maui Misumenops junctus Suman 1970 Molokai Misumenops nigrofrenatus Simon 1900 Kauai, Oahu, Hawaii Island Misumenops vitellinus Simon 1900 Kauai, Oahu, Maui, Hawaii Island Mecaphesa perkinsi Simon 1900 Oahu Mecaphesa semispinosa Simon 1900 Oahu Synaema naevigerum Simon 1900 Maui Synaema globulosum Fabricius 1775 Mt. Carmel, Israel Xysticus sp. Westchester, New York Ozyptila georgiana Keyserling 1880 Westchester, New York Thorell 1870 Maryland Misumenops asperatus Hentz 1870 Maryland sp. Indiana Diaea sp. New Zealand

various island systems worldwide by a num- collected from North America and Israel and ber of researchers: Andaman and Nicobar (Ti- others were kindly supplied by Dr. J. Robin- kader 1977), Japan (Ono 1988), Britain and son, Dr. G. Dodson, Cor Vink and Dr. W. Ireland (Roberts 1985), Puerto Rico (Petrunk- Shipley. evitch 1930), Cuba (Bryant 1940), Tonga Collection and analysis of genetic data.Ð (Marples 1959), Fiji (Marples 1957), Pitcairn DNA was extracted from the 13 Hawaiian Islands (Benton & Lehtinen 1995), Philip- species and 7 non-Hawaiian species listed in pines (Barrion & Litsinger 1995), Samoa Table 2, using a phenol-chloroform prepara- (Marples 1957), Rapa (Berland 1924), Maur- tion followed by ethanol precipitation (Pal- itius (Simon 18975), Galapagos Islands umbi et al. 1991). Voucher specimens were (Banks 1902), Tahiti (Berland 1934), and retained and will be deposited in the Bishop Marquesas Islands (Berland 1927). In the gen- Museum, Honolulu, Hawaii. A 450 bp region eration of the Misumenops species area curve, of the mitochondrial gene cytochrome oxidase Diaea species from Tonga, Fiji and Samoa I (COI) was ampli®ed for at least two indi- were substituted for Misumenops, as these viduals per species using a thermal cycler, were likely incorrectly diagnosed and are with universal primers C1-J-1718 and C1-N- closely related to the Hawaiian thomisids (Su- 2191 (Simon et al. 1994). The COI gene was man 1970). Predictions of the total expected selected because it evolves rapidly in the number of thomisid species and Misumenops third-codon position (Simon et al. 1994), pro- species in Hawaii were calculated based on viding suf®cient variation to determine rela- the species-area relationships generated. tionships between closely related species. This Collection and identi®cation of Hawaiian gene has been useful for assessing genetic di- Thomisidae.ÐHawaiian thomisid species versity and phylogenetic relationships in other were collected from native ecosystems on Hawaiian (Roderick & Gillespie Kauai, Oahu, Maui, Molokai and Hawaii Is- 1998). PCR products were sequenced using an land (Table 2). Specimens were collected by ABI 377 automatic sequencer and were beating vegetation. Sexually mature spiders aligned using Sequencher 3.0. Pairwise ge- were identi®ed to species using the Bishop netic distance (percent nucleotide difference Museum reference collection and Suman's between sequences) was calculated for all spe- (1970) key. Additional outgroup species were cies using the Kimura 2-parameter correction 74 THE JOURNAL OF ARACHNOLOGY

Figure 1.ÐSpecies-area relationship for total species in the family Thomisidae. Linear regression and a 95% CI on log-transformed data are shown. Equation of line is log(species) ϭ 0.398 log(area) Ϫ 0.917, R2 ϭ 0.70, P Ͻ 0.0001. Expected number of species in the family Thomisidae is 7, while 21 species are observed. for nucleotide bias (Kimura 1980), and a phy- pared to other island systems examined. For logenetic tree was constructed from these dis- example, Hawaii has the highest observed di- tances using a neighbor-joining algorithm in versity of Misumenops species (17), in con- PAUP* 4.0 (Swofford 1998). The Xysticus sp. trast to the 1±4 species observed in other is- sequence was used to root the resulting tree. land systems. The number of Misumenops RESULTS species on the 15 non-Hawaiian islands ap- peared to be normally distributed, and assum- Biogeographical analysis.ÐFor the spe- ing normality, Hawaii falls far above the cies-area in the family Thomisidae, a highly 99.999th percentile of the distribution. These signi®cant linear increase was found between results suggest that although thomisid diver- the number of species and area of the island sity in the Hawaiian islands is high in general, system (log-transformations, slope ϭ 0.39, R2 Misumenops constitutes a disproportionate ϭ 0.70, see Fig. 1). Perhaps not unexpectedly, amount of this diversity. Further, the restric- Hawaii has an unusually high diversity for its tion of 17 of Hawaii's 21 thomisids to a single size, falling just above the 95% con®dence in- terval for the regression. The slope of the line genus suggests that in this island indicates that an archipelago the area of Ha- archipelago is a function of autochthonous waii (28,314 sq. km), should have a total of speciation, rather than external colonization. 7 thomisid species, but 21 occur in Hawaii. Analysis of genetic data.ÐConstruction of The relationship for representatives of the ge- a distance based phylogeny from 450 bp of nus Misumenops is quite different (Fig. 2). COI revealed that the smallest genetic dis- Whether or not Hawaii is included in the re- tances were found between Hawaiian thomisid gression, there is no signi®cant relationship species (Fig. 3). Thus the Hawaiian thomisids between island size and number of Misumen- appear to be more closely related to each other ops species (R2 ϭ 0.49, P ϭ 0.43, for 15 is- than they are to representatives of Misumena, lands not including Hawaii). By any measure, Misumenoides, Diaea, Synaema, and Ozyptila. Hawaii appears to be an extreme outlier com- The Hawaiian Synaema and non-Hawaiian S. GARBÐEVIDENCE FOR A HAWAIIAN THOMISIDAE RADIATION 75

Figure 2.ÐSpecies-area relationship for species in the genus Misumenops, along with a simple linear regression on log-transformed data. Equation of line is log(species) ϭ 0.054 log(area) Ϫ 0.067, R2 ϭ 0.49, P ϭ 0.43. Expected number of Hawaiian species in the genus Misumenops is 0.6, while 17 species are observed. globulosum are extremely distant while the isid and Misumenops species, the Misumenops Hawaiian Synaema is comparatively much species represent nearly all of the thomisid di- more similar to the Hawaiian Misumenops, versity. It appears, therefore, that the number supporting Lehtinen's (1993) claim that the of successful colonizers is consistent with the Hawaiian `Synaema' is not a true Synaema. island biogeography model. However, the Small genetic distances between non-Hawai- model does not account for subsequent pro- ian Misumenops asperatus and all Hawaiian cesses that occur over evolutionary time. Misumenops species sampled suggests that the Thus, despite few colonization events, autoch- Hawaiian species are likely descended from a thonous speciation raises the species diversity Misumenops ancestor. However, because Mis- to levels higher than predicted by island area. umenops asperatus falls within the clade con- Such a pattern might suggest that most of the taining all Hawaiian thomisids, more than one available niche space for the family is being colonization event is implied for the Hawaiian occupied by species in the genus Misumenops. thomisid fauna. Sampling of many more Mis- Colonizing species may have undergone rapid umenops species from other geographic re- ecological divergence in the absence of com- gions must be conducted in order to ®rmly petition from other genera that exploit a va- establish what proportion of Hawaii's present riety of ecological strategies elsewhere. day thomisid diversity has arisen through au- Although Hawaiian Misumenops species tochthonous species radiation. are extremely diverse (Fig. 2), it is possible DISCUSSION that this result may be biased by data points The high diversity of Misumenops species representing inaccurate estimates of diversity. in Hawaii, coupled with the short genetic dis- Many of the data points used to generate the tances between species, is a pattern similar to relationships between area and diversity were that found in other Hawaiian terrestrial arthro- extracted from surveys of unequal sampling pods that have undergone species radiation effort. Further, current revisions of these is- (Roderick & Gillespie 1998). While the is- lands' spider fauna might result in different lands are exceptionally diverse in both thom- generic diagnosis of species. Consequently, 76 THE JOURNAL OF ARACHNOLOGY

Figure 3.ÐA distance based phylogeny constructed from 450 bp of COI. Genetic distances were cal- culated using Kimura's (1980) 2-parameter corrected distance measure. many of these points may represent over or tribe Misumenini Simon 1895, including spi- under estimates of true diversity. It is possible ders in the genera Misumena, Misumenoides, that a more complete data set would reveal and Misumenops (Ono 1988), are commonly that Hawaii is not overly diverse in Misumen- known as ¯ower spiders because they mimic ops or total thomisid species. However, Japan the coloration of ¯owers on which they sit in (the most thoroughly studied island group), order to capture pollinating insects (Gertsch has an area 10 times the size of Hawaii yet 1979). Recent research reveals that certain only twice the number of thomisid species species of this tribe have ecological roles as (Ono 1988). Moreover, only three of these nectivores and possible pollinators (Pollard et species are Misumenops. The relatively small al. 1995). While genetic data suggest that the genetic distances among Hawaiian species are Hawaiian thomisids are descendants of ¯ower consistent with the hypothesis that the high spiders, Hawaiian thomisids are extremely di- morphological and ecological diversity of Ha- verse in their substrate af®nities. For example, waiian thomisids is primarily the result of au- the green and brown speckled Misumenops tochthonous radiation. editus, endemic to the summit of Mt. Kaala, The Hawaiian Misumenops possess excep- Oahu, is perfectly camou¯aged amongst its tional ecological diversity when compared to primary microhabitat of moss patches. Like- their continental congeners. Members of the wise, M. aridus and M. nigrofrenatus are well family Thomisidae are well known for their hidden on their substrate of white ®lamentous employment of mimicry to ambush prey. The lichen. Other species are more speci®c to GARBÐEVIDENCE FOR A HAWAIIAN THOMISIDAE RADIATION 77 green foliage. Many Hawaiian Misumenops desÃles õ Juan Fernandez. The Natural History of that are ecologically separated as a result of Juan Fernandez and Easter Island, 3:419±437. differential substrate af®nity are sympatric Berland, L. 1927. Notes sur les AraigneÂes recueil- and may be very close relatives (Suman lies aux eles Marquises par le R.P. SimeÂn Del- 1970). mas. Bull. Du MuseÂum National d'Histoire Na- turelle, Paris, 38:366-368. In order to appreciate fully the extent of Berland, L. 1934. Les AraigneÂes de Tahiti. Bull. species radiation in the Hawaiian Misumen- Bernice P. Bishop Museum, 113:97±107. ops, a complete phylogenetic construction is Bryant, E.B. 1940. Cuban spiders in the Museum warranted. Only with a well-supported phy- of Comparative Zoology. Bull. Mus. Comp. logenetic hypothesis can the idea of species Zool., 86(7):247±554. radiation among the Hawaiian thomisids be Carson, H.L. 1994. Genetical processes of evolu- tested rigorously. From such a hypothesis, one tion of high oceanic islands. Pp. 259±262. In A can determine the number of colonization Natural History of the Hawaiian Islands. (E.A. events and the ecological diversity of this Kay, ed.). Univ. Hawaii Press, Honolulu, Hawaii. group. It is clear from data presented here that Carson, H.L & D.A. Clague. 1995. Geology and biogeography of the Hawaiian Islands. Pp. 14± the Hawaiian Misumenops do not ®t the clas- 29. In Hawaiian Biogeography, Evolution on a sical model for island biogeography as they Hot Spot Archipelago. (W.L. Wagner & V.A. are species rich in an isolated and small island Funk, eds.), Smithsonian Institution Press, Wash- area. ington, D.C. Coddington, J.A. & H.W. Levi. 1991. Systematics ACKNOWLEDGMENTS and evolution of spiders (Araneae). Ann. Rev. I thank Rosemary Gillespie, George Rod- Ecol. Syst., 22:565±592. erick, A. Bohonak, and two anonymous re- Gertsch, W.J. 1979. American Spiders. 2nd ed. Van viewers for help in preparation of this manu- Nostrand Reinhold Co., New York. script, B. Thorsby, M. Rivera, and J. Gubili Gillespie, R.G. 1994. Hawaiian spiders of the ge- for laboratory assistance, M. Heddle, C. Ew- nus Tetragnatha: III. Tetragnatha acuta clade. J. Arachnol., 22:161±168. ing, B. Thorsby, M. Rivera, A. Vandergast, D. Gillespie, R.G., H.B. Croom & L. Hasty. 1997. Preston, A. Asquith, A. Medieros and E. Lar- Phylogenetic relationships and adaptive shifts son for assistance in collecting Hawaiian spi- among major clades of Tetragnatha spiders (Ar- ders, W. Shipley, C. Vink, J. Robinson and G. aneae: Tetragnathidae) in Hawaii. Paci®c Sci., Dodson for shipment of non-Hawaiian thom- 51(4):380±394. isids, S. Swift at the Bishop Museum for ac- Gillespie, R.G. & N. Reimer. 1993. The effects of cess to collections, the managers of Volcanoes alien predation of ants (Hymenoptera: Formici- and Haleakala national parks, Hawaii State dae) on the Hawaiian endemic spiders (Araneae: Dept. of Fish and Wildlife reserves and The Tetragnathidae). Paci®c Sci., 47(1):21±33. Nature Conservancy of Hawaii's preserves for Gillespie, R.G., M.A. Rivera & J.E. Garb. 1998. permission to collect thomisids. This work is and phylogeography of Hawaiian Ar- aneae. Bull. British Arachnol. Soc., 11:41±51. partly supported by a student research grant Grant, B.R.& P.R. Grant. 1989. Evolutionary Dy- from the University of Hawaii Ecology, Evo- namics of Natural Populations. Univ. Chicago lutionary and Conservation Biology Program Press, Chicago. and from AAS, as well as NSF grants to R. Howarth, F.G. & W.P. Mull. 1992. Hawaiian In- Gillespie. sects and Their Kin. Univ. Hawaii Press, Hono- lulu. LITERATURE CITED Kimura, M. 1980. A simple method for estimating Banks, N. 1902. 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