All are one and one is all: sexual uniformity among widely separated populations of the North American seal salamander, Desmognathus monticola

The Modern Synthesis of the mid‐20th century effectively buried typological definitions and descriptions of species and their boundaries. This interment is well supported by the large number of animal species for which substantial levels of sexual incompatibility have been found among conspecific populations, including some species of North American desmognathine salamanders that have restricted geographical ranges. We tested for sexual incompatibility and variation in sexual signals and responses among widely separated populations of the broadly distributed seal salamander, Desmognathus monticola . Levels of sexual incompatibility and differences in behaviour patterns exhibited during courtship and mating were modest to non‐existent among these populations, despite the considerable geographical distances separating some of them. Our data are not consistent with results obtained in the majority of similar studies that have been conducted on congeneric species. For the seal salamander, we cannot reject the applicability of a typological species definition based on sexual compatibility and uniformity in the ethology of courtship among populations. We present five hypotheses (not necessarily mutually exclusive) that may explain our results. We suggest that recent range expansion, perhaps coupled with contemporary gene flow, may best explain sexual uniformity among populations of the seal salamander. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78 , 1–10.