Molecular biogeography of the Pacific

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Species-range information forms the empirical data base for much of biogeography, but even with a huge amount of data on species occurrences, many of the ecological and evolutionary processes generating biogeographic patterns remain obscure. Molecular genetic data from closely related, widely distributed species can help address biogeographic mechanisms by (1) providing independent evidence for genetic boundaries between cryptic species, (2) estimating species divergence times, (3) providing phylogenetic reconstructions of species divergence patterns, and (4) allowing us to examine the geography of allelic variants within species and ask if intra-specific alleles show the same biogeographic patterns as do species. Data from mitochondrial DNA variation in Pacific sea urchins and butterfly fishes show that congeneric species diverged within the Pleistocene. Thus, the processes that generate species diversity patterns probably have been acting throughout the recent past, and are ongoing aspects of Pacific marine biology. Phylogenetic analysis of mtDNA variants suggests that sea urchin species arise throughout the Pacific, with some originating by peripheral speciation and some evolving in the high diversity center of the Indo-West Pacific. Clines of mtDNA variation within species are similar to diversity clines in the entire fauna. Similar biogeographic patterns for species and for alleles within species may provide unique clues about the processes that generate biological diversity both within and between species.