Contemporary hybridization between female mule deer and male white-tailed deer in west Texas differs from the hypothesized sex mating patterns recovered from ancient hybridization events

Introgressive hybridization between members of Odocoileus was examined using the mitochondrial cytochrome-b (maternal marker) and paternal sex-determining region Y ( Sry) genes. Eight out of 130 free-ranging individuals from the Panhandle and Trans-Pecos regions of Texas were determined to possess the mitochondrial haplotype of mule deer ( Odocoileus hemionus (Rafinesque, 1817)) and the paternal haplotype of white-tailed deer ( Odocoileus virginianus Rafinesque, 1832). Results indicated that hybridization between deer species in Texas (6.15%) was more broadly distributed than previously reported. Previous studies demonstrated that ancient hybridization events (1.32 mya) involved the capture of the white-tailed deer mitochondrial genome by mule deer, indicating a male mule deer × a female white-tailed deer directionality relevant to hybridization. Alternatively, contemporary hybridization events indicated a reversal in directionality and suggested a cross between a female mule deer × a male white-tailed deer. The Sry gene and species assignment based on morphological characters consistently were in agreement. Further, phylogenetic relationships between Odocoileus virginianus couesi and Odocoileus hemionus eremicus warrant additional investigation as recent hybridization (>200 years) may be a mechanism that allowed these two subspecies to evolve a unique evolutionary trajectory.