Asymmetric reproductive isolation between terminal forms of the salamander ring species Ensatina eschscholtzii revealed by fine-scale genetic analysis of a hybrid zone

Our results are consistent with a tension zone trapped at an ecotone, with gene combinations characteristic of klauberi showing up on the eschscholtzii side of the zone due to asymmetric hybridization. We suggest that the observed asymmetry is best explained by increased discriminatory power of eschscholtzii females, or asymmetric postzygotic isolation. The relatively high frequency of hybrids, particularly F1s, contrasts with other contacts between the terminal forms, and with other contacts between other divergent Ensatina lineages, highlighting the diverse outcomes of secondary contact within a single species complex.