Exploring species boundaries of the spotted ground squirrel (Xerospermophilus spilosoma) complex

Límites de especies del complejo Xerospermophilus spilosoma

Abstract

Xerospermophilus spilosoma exhibits notable geographic and morphological variation, prompting a debate over its taxonomic status. Currently, it is unclear whether it represents a single highly variable species or a complex of cryptic species that includes X. perotensis. Although the latter has a larger body size and a distinctive dorsal pattern, current genetic analyses do not support its recognition as a separate species. This study aimed to delimit potential evolutionary units within the X. spilosoma complex. Twenty-four sequences of the mitochondrial cytochrome b gene were analyzed using 690-bp fragments from X. spilosoma and X. perotensis specimens collected from eight locations. Phylogenetic and divergence time inferences were estimated using Maximum Likelihood and Bayesian Inference, along with analyses of genetic distances and haplotype networks. Three species delimitation methods (ABGD, PTP, and GMYC) were applied, and the ecological uniqueness and areas of overlap within and between species of the X. spilosoma complex were assessed. Four lineages comprising 22 unique haplotypes were identified, with interpopulation genetic distances ranging from 3 % to 6 %. Species delimitation methods suggested between one and four potential species. Meanwhile, the comparison of ecological niches revealed limited overlap. Genetic and environmental evidence indicate that X. spilosoma comprises at least three evolutionarily independent lineages. The complex originated in the Miocene, more than 5 million years ago, with divergence events concentrated between 3.5 and 1.5 million years ago, in accordance with geographical barriers such as Río Grande and the Nazas River and the Trans-Mexican Volcanic Belt. These results highlight the need to conserve these populations as independent evolutionary units, particularly the Perote population, given its isolation and ecological and genetic uniqueness.