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

Incilius marmoreus inhabits an extensive range along the Pacific Coast of Mexico and a smaller allopatric region in the State of Veracruz, exhibiting an unusual distribution among herpetofauna. Günther (1901) classified the Pacific coastal toads Bufo argillaceus and B. lateralis as conspecific with Incilius [Bufo] marmoreus, which has its type locality in Veracruz. Here, we adopt a multidisciplinary 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 whilst coalescent analyses recovered a north–south split along the Pacific Coast estimated to have occurred ∼0.86 Mya followed by a shallow east–west split in the southern lineage that separates the Pacific coastal populations and the allopatric population in Veracruz ∼0.33 Mya. This species displays marked morphological and genetic diversity throughout its range, but this variation appears to be consistent with gene flow across contiguous populations rather than the existence of independent evolutionary lineages. The processes leading to the geographic isolation of the population on the coast of Veracruz remain uncertain, but we hypothesize that climatic and vegetation changes in the Late Pleistocene may have played a role.