Abstract
The accurate delimitation of evolutionary population units represents an important component in phylogeographic and conservation genetic studies. Here, we used a combined population assignment and historical demographic approach to study a complex of ecomorphologically distinctive populations of B lack S alamanders ( A neides flavipunctatus ) that are parapatrically distributed and meet at a three‐way contact zone in north‐western C alifornia. We used mitochondrial tree‐based and multilocus clustering methods to evaluate a priori two‐ ( N orthern and S outhern) and three ( N orthern, C oast and I nland) population hypotheses derived from previous studies. Mitochondrial results were consistent with the two‐ and three‐population hypotheses, while the nDNA clustering results supported only the two‐population hypothesis. Historical demographic analyses and mtDNA gene divergence estimates revealed that the N orthern and S outhern populations split during the P liocene (2–5 Ma). Subdivision of the S outhern population into C oast and I nland populations was estimated to be late P leistocene (0.24 Ma), although our mtDNA results suggested a P liocene divergence. Effective gene flow estimates (2 N e m ) suggest that either the two‐ or three‐population hypotheses remain valid. However, our results unexpectedly revealed that the N orthern population might instead represent two parapatric populations that separated nearly 4 Ma. These results are surprising because the Pliocene divergence between these ecomorphologically conservative forms is similar or older than for the ecomorphologically divergent C oast and I nland sister populations. We conclude that B lack S alamanders in north‐western C alifornia belong to at least three or four populations or species, and these all meet criteria for being E volutionary S ignificant U nits or ‘ ESUs ’ and therefore warrant conservation consideration.