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

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
split times estimated to be in the last 50,000 years. Subsequent
morphological analyses detected differences among the three groups,
including male colour pattern in life, 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), rather
than one, and the study highlights the daunting yet critical task of
describing species diversity during a period of unprecedented diversity
loss.