Phylogeographic insights into the ecology and evolution of Indo-Pacific reef fishes

While recent direct evidence of high local larval retention represents an enormous advancement in our understanding of marine larval behavior and dispersal, the translation of these findings from a few small-range species to a rule for marine populations as a whole rests on tentative inferential evidence. Rapidly accumulating genetic data does in some cases support the proposal of high local larval retention, with many small range reef fishes exhibiting pronounced genetic subdivision over very fine spatial scales. However, these patterns contrast starkly with evidence of broad genetic connectivity in widely distributed reef fishes. A general pattern of wide distribution and long-distance connectivity is emerging, with the relationship between range size and degree of genetic structuring supported in a molecular survey of endemic and non-endemic Hawaiian fishes (Chapter 2). What is apparent from the genetic data is that broad distribution does not necessarily equate with increased opportunities for the establishment of reproductive isolation. Conversely, small range fishes regularly exhibit pronounced fine-scale population differentiation. While limited dispersal may confer a competitive advantage by increasing the likelihood of local adaptation, potential adaptive benefits may be offset by an increased possibility of extinction due to environmental change or stochastic loss of diversity. Evidence of a Hawaiian origin and subsequent colonization of the West Pacific for the reef fish, Zebrasoma flavescens, suggests evolutionary bet hedging, with colonization of the West Pacific potentially increasing Z. flavescens long-term viability (Chapter 3). Larval export from Hawaii has been demonstrated in a growing number of reef fishes and invertebrates, yet whether evidence of larval connectivity over tens of thousands of kilometers translates into demographically significant connectivity at scales greater than recent direct larval tracking would suggest is still to be determined. Nevertheless, concordant biogeographic and phylogeographic patterns indicate that many marine species are capable of regularly exchanging migrants over thousands of kilometers (Chapter 4). In all likelihood, marine populations range from fully open to fully closed, with the extent of larval exchange differing considerably between species and regions.