Hybridization and Genetic Structure in Phenotypic Spotted Bass in Texas

Hybridization is common in fishes and can result in a wide range of outcomes. The capture of a world record phenotypic Guadalupe Bass Micropterus treculii raised questions about potential hybridization with Spotted Bass M. punctulatus . Subsequent, limited genetic sampling from the drainage (Colorado River) did not indicate hybridization in the world record sample or other phenotypic Guadalupe Bass, but phenotypic Spotted Bass produced unexpected genotypes. This called into question the assumed distribution of Spotted Bass in Texas. To address this disconnect, phenotypic Spotted Bass were acquired from drainages surrounding the Colorado River, ranging from central Texas to the Texas–Louisiana border, and the number of sequenced loci was expanded from one to seven. Results indicated that the westernmost extent of nonintrogressed Spotted Bass populations in Texas was the Trinity River. Phenotypic Spotted Bass west of this drainage were identified as Guadalupe Bass or hybrids. Admixed individuals identified in the San Antonio and Brazos River drainages (and previously in the Colorado River) may represent part of a hybrid zone. We also found that Spotted Bass from the Trinity River exhibited relatively large genetic divergence from Spotted Bass to the east and may represent the product of a vicariance event. Finally, we confirmed one mitochondrial and two nuclear taxa‐specific genetic markers for the efficient discrimination of these congeners and their hybrids. These markers should be useful for resource agencies attempting to enforce management regulations given the difficulty of identifying Spotted Bass by phenotype.