Identifying a potentially cryptic species Gila in Sonora, Mexico

Authors: Ballesteros-Cordova, Carlos A., Varela-Romero, Alejandro, Ruiz-Campos, Gorgonio, Findley, Lloyd, Grijalva-Chon, Jose M., Gutiérrez-Millán, Luis E.

Year: 2015 (xlvii)

Abstract

The Desert Chub, Gila eremica DeMarais, 1991, is an endemic species in Sonora State in Northwest Mexico. It has been collected in and was described from the Sonora and Matape river basins, with a single record (perhaps dubious) from the Moctezuma River in the upper Yaqui River basin. Recently, two new populations of G. cf. eremica were discovered in large spring-fed pools (tinajas) in two subtropical canyons of the Arroyo El Tigre sub-basin, which intermittently drains the eastern flank of the ruggedly volcanic Sierra El Aguaje range within the Matape River basin, near the towns of San Carlos and Guaymas, Sonora. These new populations are distantly isolated from populations of Gila eremica in the Sonora and Matape drainages. Using several biological criteria, the taxonomic identities of these two new populations were evaluated against known populations of Gila eremica and other selected species of Gila. Based on box-truss protocol, 33 morphometric and six meristic characters were compared in 219 specimens from several populations Gila in Sonora, including all known populations of Gila eremica Both meristics and standardized measures were analyzed by means of a discriminant function analysis (DFA). Tree diagrams based on squared Mahalanobis distances, as well as scatterplots of centroids, showed the newly discovered populations of G. cf. eremica from the Arroyo El Tigre sub-basin to be morphologically divergent with respect to known populations of Gila eremica, as well as the other species analyzed (G. purpurea, G. ditaenia, G. minacae). Analyses showed that 14 morphological and two meristic characters differentiate G. cf. eremica from nominal Gila eremica. Phylogenetic analysis (Maximum Likelihood) using mitochondrial gene Cyt-b of G. cf. eremica, and including sequences of all reported species of the genus, detected distinct geographical clades within the Gila eremica species-complex, with a clade for populations from the Sonora River basin (Sonora and San Miguel rivers sub-basins), and a clade for populations from the Matape River basin (Matape River sub-basin and Arroyo El Tigre sub-basin) showing close relationship of G. cf. eremica (Arroyo El Tigre sub-basin) with populations of G. eremica (Matape River sub-basin) as its sister clade. Populations of G. cf. eremica (Arroyo El Tigre sub-basin) showed a putative ancestor with respect to populations of G. eremica from the Matape River basin.