A total evidence approach justifies taxonomic splitting of the endangered Pecos gambusia into three species

TL;DR

This study shows that the endangered Pecos gambusia is actually three distinct species, based on genetic and morphological evidence.

Contribution

The study uses population genomics and morphology to justify splitting the Pecos gambusia into three new species.

Findings

Genetic data revealed three distinct groups with high divergence (F’ST = 0.55–0.76).

Phylogenetic analysis identified three clades with divergence times within the last 50,000 years.

Morphological differences, including male color patterns and fin rays, support the split into three species.

Abstract

Gambusia nobilis is a federally endangered species found across a fragmented distribution within the Pecos River Drainage of Texas and New Mexico, USA. Drought, human water usage, and potential hybridization and competition with introduced congeners threaten species persistence. Therefore, a population genomics study was conducted to provide critical information for conservation planning. Unsupervised clustering suggested hierarchical structure, with a primary K = 3, and deep divergences were detected among samples grouped into the Leon Creek watershed, the Toyah Creek watershed, and water bodies within the Bitter Lake National Wildlife Refuge (F’ST = 0.55–0.76 for putatively neutral data). Phylogenetic analyses showed three distinct clades corresponding to these groups, with divergence times estimated to be in the last 50 000 years. Complimentary morphological analyses detected differences among the three groups, including features of male colour pattern, and the number of caudal-fin rays in both sexes. Taken as a whole, the results indicate that the endangered G. nobilis comprises three species (two of which are named herein as G. pyrros n. sp. and G. echelleorum n. sp.), rather than one, and the study highlights the daunting yet critical task of documenting species diversity during a period of unprecedented diversity loss.

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