Failed species, innominate forms, and the vain search for species limits: cryptic diversity in dusky salamanders ( Desmognathus ) of eastern Tennessee

Cytochrome B sequences and allozymes reveal complex patterns of molecular variation in dusky salamander ( Desmognathus ) populations in eastern Tennessee. One group of allozymically distinctive populations, which we refer to as the Sinking Creek form ( SCF ), combines morphological attributes of Desmognathus fuscus with cytB sequences characteristic of Desmognathus carolinensis . This form is abruptly replaced by D. fuscus just north of Johnson City, TN with no evidence of either sympatry or gene exchange. To the south, allozymic markers indicate a broad zone of admixture with populations characterized by distinct cytB sequences and that may or may not be ultimately referable to Desmognathus conanti . A third distinctive group of populations, which we refer to as the Lemon Gap form ( LGF ), occurs in the foothills of the Great Smoky and southern Bald Mountains and exchanges genes with Desmognathus santeetlah along the escarpment of the Great Smokies, D. carolinensis in the southern Bald Mountains, and populations of a different haplotype clade in the Ridge and Valley. We treat all these as innominate forms that may represent “failed species,” recognizing that it may never be possible to reconcile species limits with patterns of phylogeny, morphology, and gene exchange in these salamanders.