Mixed Support for Pleistocene Sea-Level Fluctuations in Promoting the Diversification of Anole Lizards in the...

In the Pleistocene, climatic changes resulted in cycles of sea-level fluctuation that periodically fragmented islands into aggregate island complexes. These temporary saltwater barriers between islands within an island bank had the potential to decrease migration between populations on separate islands, resulting in increased genetic divergence and potentially speciation. In the Lesser Antilles, Anolis lizards (anoles) are distributed across island banks that vary in distance and water depth between islands, making them excellent candidates for studying how different barriers shape patterns of genetic diversity. Here, we focused on anoles found across the St. Kitts Bank (A. bimaculatus, A. schwartzi), Anguilla Bank (A. gingivinus), and Barbuda Bank (A. leachii, A. wattsi) to test the hypothesis that populations separated by narrower and shallower marine barriers are more genetically similar to one another than populations on more distant islands or those separated by deeper water. Using a combination of mitochondrial and nuclear genomic DNA, we found a spectrum of population genetic structure ranging from weak but detectable structure (A. gingivinus, Anguilla Bank and A. leachii, Barbuda Bank) to pronounced (A. bimaculatus and A. schwartzi, St. Kitts Bank) and even species divergence (A. wattsi complex, Barbuda Bank). The extent of genetic divergence, however, did not consistently correspond to island bathymetry. Our demographic analyses for each currently recognized species supported a model of divergence with gene flow, consistent with a history of intermittent migration between present-day islands. Collectively, these results support a partial role for sea-level fluctuations in the Pleistocene structuring current patterns of genetic diversity in Lesser Antillean anoles.