Molecular assessment of nonnative status for Largespring Gambusia (Poeciliidae: Gambusia geiseri) in West Texas: Conservation value of nonnative populations

Authors: Echelle, Anthony A.*1, Schwemm, Michael R.2, Echelle, Alice F.1, Turner, Thomas F.3, Wilson, Wade2

Year: 2015 (xlvii)

Abstract

Management errors can occur when native species are incorrectly treated as non-natives. A potential example is Gambusia geiseri, a species considered endemic to the Comal and San Marcos rivers on the east side of the Edwards Plateau in Texas. It has been assumed that populations in the Colorado River and Rio Grande basins in Texas were introduced by humans in the 1930s. This assumption was somewhat questionable because of the paucity of early records of Gambusia from the region. Further, a congener, G. speciosa, in the Rio Grande basin is polymorphic for an apparently “foreign” mtDNA haplotype that is most similar to, but 2% divergent from, a haplotype previously reported for eastern G. geiseri. This suggested that Rio Grande populations of G. geiseri might represent a divergent, native lineage of the species. To address this, we surveyed mitochondrial (cytb) and nuclear (S7 intron 1) variation in 125 G. geiseri representing all of six local areas supporting the species. Collections from the Rio Grande and Colorado River were either fixed for one or another of the markers detected in the San Marcos-Comal area or they were polymorphic for one of those haplotypes and weakly divergent (G. geiseri and fish assemblages supporting nonnative populations of the species are discussed.