Vicariance and dispersal across an intermittent barrier: population genetic structure of marine animals across the Torres Strait land bridge
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Biogeographic barriers, some transitory in duration, are likely to have been important contributing factors to modern marine biodiversity in the Indo-Pacific region. One such barrier was the Torres Strait land bridge between continental Australia and New Guinea that persisted through much of the late Pleistocene and separated Indian and Pacific Ocean taxa. Here, we examine the patterns of mitochondrial DNA diversity for marine animals with present-day distributions spanning the Torres Strait. Specifically, we investigate whether there are concordant signatures across species, consistent with either vicariance or recent colonization from either ocean basin. We survey four species of reef fishes (Apogon doederleini, Pomacentrus coelestis, Dascyllus trimaculatus, and Acanthurus triostegus) for mtDNA cytochrome oxidase 1 and control region variation and contrast these results to previous mtDNA studies in diverse marine animals with similar distributions. We find substantial genetic partitioning (estimated from F-statistics and coalescent approaches) between Indian and Pacific Ocean populations for many species, consistent with regional persistence through the late Pleistocene in both ocean basins. The species-specific estimates of genetic divergence, however, vary greatly and for reef fishes we estimate substantially different divergence times among species. It is likely that Indian and Pacific Ocean populations have been isolated for multiple glacial cycles for some species, whereas for other species genetic connections have been more recent. Regional estimates of genetic diversity and directionality of gene flow also vary among species. Thus, there is no apparent consistency among historical patterns across the Torres Strait for these co-distributed marine animals.
KeywordsAustralia Coalescence Coral Triangle Gene flow Comparative phylogeography Planktonic larval dispersal
Thanks to J. D. Aguirre-Davies and F. MacKenzie for assistance in the field, and two anonymous reviewers for comments. The Computational Biology Service Unit from Cornell University, which is partially funded by Microsoft Corporation, was used for some analyses. Funding for this work was provided by the Australian Research Council (DP0878306 to CR), and the World Wildlife Fund (to EAT). Fishes were collected under permits from the Department of the Environment, Water, Heritage, and the Arts (AU-COM2008042), Great Barrier Reef Marine Park Authority and Department of Environment and Resource Management (G08/28114.1), Queensland Government Dept. of Primary Industries & Fisheries (118636), and WA Department of Environment and Conservation (SF006619). This study complies with Animal Ethics standards for the University of Queensland (permit SIB/817/08/ARC).
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