Phylogenomics and species delimitation in the brown snake Storeria dekayi (Natricidae)

The brown snake, Storeria dekayi, is distributed across southeastern Canada, the eastern United States, and eastern Mexico, with isolated records in Central America. Despite its broad range, S. dekayi is currently recognized as a single species. Historically, eight subspecies were described based primarily on head coloration patterns, but subsequent genomic analyses of populations from the U.S.A led to their synonymization. Recently, a population discovered in the Cuatro Cienegas Basin, Coahuila, Mexico has been suggested to represent an undescribed endemic species. The aim of this study is to investigate the relationships within S. dekayi, with an emphasis on the previously unstudied populations from Mexico and Central America. To this end, we generated genomic data (ddRADseq) to conduct phylogenetic analyses, species-tree estimation, population-structure analyses, and species delimitation. Concatenated likelihood analyses estimated a tree in which populations of S. dekayi from the south-central U.S. were paraphyletic relative to an undescribed species from the Cuatro Cienegas Basin. Population structure and species delimitation analyses suggest the existence of three distinct species, including the populations from eastern North America (recognized as S. dekayi), the population from Cuatro Cienegas, and the populations of S. dekayi from eastern Mexico and Central America. However, we conservatively recognize only two species.