CONTRASTING QUATERNARY HISTORIES IN AN ECOLOGICALLY DIVERGENT SISTER PAIR OF LOW‐DISPERSING INTERTIDAL FISH ( XIPHISTER ) REVEALED BY MULTILOCUS DNA ANALYSIS

Recurrent glacial advances have shaped community histories across the planet. While biogeogrphic responses to glaciations likely varied with latitude, the consequences for temperate marine communities histories are less clear. By coalescent analyses of multiloci DNA sequence data (mitochondrial DNA control region, α‐enolase intron, and α‐tropomyosin intron) collected from a low‐dispersing sister pair of rocky intertidal fishes commonly found from southeastern Alaska to California ( Xiphister atropurpureus and X. mucosus ), we uncover two very different responses to historical glaciations. A variety of methods that include a simulation analysis, coestimates of migration and divergence times, and estimates of minimum ages of populations sampled up and down the North American Pacific coast all strongly revealed a history of range persistence in X. atropurpureus and extreme range contraction and expansion from a southern refugium in X. mucosus . Furthermore, these conclusions are not sensitive to the independent estimates of the DNA substitution rates we obtain. While gene flow and dispersal are low in both species, the widely different histories are rather likely to have arisen from ecological differences such as diet breadth, generation time, and habitat specificity.