| Summary: | Summary In vicariance biogeography, the traditional focus on solely determining area relationships can obscure biologically interesting complexity. Even in the case of neighboring sister areas, the rise and fall of barriers to dispersal can yield a complex pattern of vicariance and interchange. Vicariance biogeographers view incongruent historical patterns as noise that must be filtered out. Here, we sharpen the focus of vicariance biogeography, and attempt to identify organismal characteristics that unite sets of taxa with congruent histories. Emphasizing examples from coastal marine invertebrates, we apply this perspective to two well-studied model systems: the southeastern United States, and the trans-Arctic interchange through the Bering Strait. In both systems, populations from neighboring areas tend to show either great genetic similarity, usually inferred to result from continuing gene flow, or reciprocal monophyly accompanied by deep genetic divergence. Because dispersal ability is a poor predictor of which taxa fall in either category, we consider the possibility that genetic similarities often attributed to continuing gene flow may result instead from extinction in one area followed by recolonization from the other. Similarly, reciprocal monophyly between neighboring areas suggests that taxa in those areas have resisted recent local extinction. Our perspective shifts focus away from larval dispersal ability, which has long dominated molecular marine biogeography. Instead, we can focus on extinction itself, asking why taxa showing reciprocal monophyly have resisted local extinction. A focus on extinction and recolonization is especially fruitful for understanding the trans-Arctic interchange. In group after group, researchers have found genetic evidence consistent with local extinction in the NW Atlantic followed by recolonization either from the NE Atlantic or from the North Pacific. In general, taxa which are restricted to rocky substrata appear to have been more prone to local extinction. The ability ...
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