Resolving the Taxonomic Status of the Marbled Toad (Bufonidae: Incilius marmoreus ): 2RAD-based Phylogeography Including an Isolated Population in Veracruz, Mexico

Inhabiting an extensive range along the Pacific Coast of Mexico and a smaller allopatric region in the State of Veracruz, Incilius marmoreus has an unusual distribution amongst herpetofauna. Günther (1901) considered the Pacific coastal toads Bufo argillaceus and Bufo lateralis to be conspecific with Incilius [Bufo] marmoreus, for which the type locality is in Veracruz. Here, we adopt an integrative approach to reevaluate the phylogeography and taxonomy of I. marmoreus by gathering and analyzing morphological data and conducting phylogenetic and population genetic analyses from genome-wide SNP data. Our results uphold the current taxonomy by concurring with Günther (1901). Our phylogenetic and population genetic analyses suggest that I. marmoreus from Veracruz are closely related to those from Oaxaca, and our coalescent analyses recovered a north–south split along the Pacific Coast estimated to have occurred ∼1.29 Mya followed by a shallow east–west split in the southern lineage that separates the Pacific coastal populations and the allopatric population in Veracruz ∼0.46 Mya. Present gene flow throughout the western range is evident, and the species displays a marked amount of morphological and genetic diversity throughout its range. The events that led to the formation of the population isolated on the coast of Veracruz remain uncertain, but we hypothesize that climatic and vegetation changes in the Late Pleistocene may have played a role.