Island hopping across the central Pacific: mitochondrial DNA detects sequential colonization of the Austral Islands by crab spiders (Araneae: Thomisidae)
Authors: Garb Jessica E. , Gillespie Rosemary G. 
Published: January 2006

Aim Phylogenetic studies concerning island biogeography have been concentrated in a fraction of the numerous hot‐spot archipelagos contained within the Pacific Ocean. In this study we investigate relationships among island populations of the thomisid spiderMisumenops rapaensisBerland, 1934across the Austral Islands, a remote and rarely examined southern Pacific hot‐spot archipelago. We also assess the phylogenetic position ofM. rapaensisin relation to thomisids distributed across multiple Polynesian archipelagos in order to evaluate the proposed hypothesis that thomisid spiders colonized Polynesia from multiple and opposing directions. The data allow an examination of genetic divergence and species accumulation in closely related lineages distributed across four Polynesian archipelagos.

Location The study focused on four Polynesian hot‐spot archipelagos: the Austral, Hawaiian, Marquesan and Society islands.

Methods Mitochondrial DNA sequences comprisingc. 1400 bp (portions ofcytochrome oxidase subunit I, ribosomal16SandNADH dehydrogenase subunit I) were obtained from thomisid spiders (64 specimens, representing 33 species) collected in the Australs, the Hawaiian Islands, the Society Islands, the Marquesas, Tonga, Fiji, New Zealand, New Caledonia and North and South America. Phylogenetic analyses using parsimony, maximum‐likelihood and Bayesian approaches were employed to resolve relationships ofM. rapaensisto other PolynesianMisumenopsand across the Austral Islands.

Results Rather than grouping with otherMisumenopsspp. from the archipelagos of the Society Islands, Marquesas and Hawaiian Islands,M. rapaensisappears more closely related toDiaeaspp. from Tonga, Fiji, New Zealand and New Caledonia. Phylogenetic analyses strongly supportM. rapaensisas monophyletic across the Austral Islands.Misumenops rapaensissampled from the two older islands (Rurutu and Tubuai) form reciprocally monophyletic groups, while individuals from the younger islands (Raivavae and Rapa) are paraphyletic. Across the Austral Islands,M. rapaensisexhibits a surprising level of genetic divergence (maximally 11.3%), an amount nearly equivalent to that found across the 16 examined Hawaiian species (14.0%).

Main conclusions Although described as a single morphologically recognized species, our results suggest thatM. rapaensiscomprises multiple genetically distinct lineages restricted to different Austral Islands. Phylogenetic relationships among the island populations are consistent with sequential colonization of this lineage down the Austral archipelago toward younger islands. Analyses support the hypothesis that thomisid spiders colonized the central Pacific multiple times and suggest thatM. rapaensisarrived in the Austral Islands from a westward direction, whileMisumenopsfound in neighbouring archipelagos appear to be more closely related to New World congeners to the east. Finally, our data detect asymmetrical rates of morphological evolution and species diversification following colonization of four different Polynesian archipelagos.