Island hopping across the central Pacific:: mitochondrial DNA detects sequential colonization of the Austral Islands by crab spiders (Araneae: Thomisidae)

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 spider Misumenops rapaensis Berland, 1934 across the Austral Islands, a remote and rarely examined southern Pacific hot-spot archipelago. We also assess the phylogenetic position of M. rapaensis in 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 comprising c. 1400 bp (portions of cytochrome oxidase subunit I, ribosomal 16S and NADH 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 of M. rapaensis to other Polynesian Misumenops and across the Austral Islands. Results Rather than grouping with other Misumenops spp. from the archipelagos of the Society Islands, Marquesas and Hawaiian Islands, M. rapaensis appears more closely related to Diaea spp. from Tonga, Fiji, New Zealand and New Caledonia. Phylogenetic analyses strongly support M. rapaensis as monophyletic across the Austral Islands. Misumenops rapaensis sampled 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. rapaensis exhibits 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 that M. rapaensis comprises 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 that M. rapaensis arrived in the Austral Islands from a westward direction, while Misumenops found 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.