Genetic interactions between two species of North American deer, Odocoileus virginianus and Ococoileus hemionus

Abstract

The fertility of a first generation male hybrid deer produced from a cross between a male Odocoileus virginianus (white-tailed deer) and a female O. hemionus (mule deer) was assessed. Examination of mitotic chromosomes and NOR expression, synaptonemal complex formation and chromosome pairing during meiosis, flow cytometry determination of DNA content and sperm production, and inheritance patterns of nuclear gene products revealed no genetic anomalies, suggesting normal hybrid fertility. Allozymic variation from 25 genetic loci was examined from 201 animals from 31 localities. The products of two loci (acid phosphatase and albumin) clearly separated individuals of both species in > 98% of the animals examined. Nei's genetic distance values were 0.135 between the two species and 0.031 between mule and black-tailed deer (O. hemionus). No F1 hybrids were detected; however, all animals that were heterozygous at one diagnostic locus were from areas of mosaic habitat supporting populations of both species. Changing environmental conditions that provide one species a competitive advantage over the other may produce temporal areas amendable to hybridization. Nevertheless, the limited amount of introgression does not present a significant threat to the uniqueness of the nuclear gene pools or the genetic integrity of either species. Mitochondrial DNA (mtDNA) restriction site variation was examined from 249 animals from 33 localities. Twenty-three mtDNA haplotypes were found using 6bp recognizing endonucleases. Six of these haplotypes were shared between the two species. A subset of individuals with identical mtDNAs, based on 6bp DNA sequences, also was examined using 4bp recognizing endonucleases. In contrast to the current taxonomy and data from published allozyme studies, Southwestern white-tailed and mule deer mtDNAs are more closely related to one another than are the mtDNAs of mule and black-tailed deer. This observation supports the hypothesis that historic hybridization between white-tailed and mule deer in the Southwest has resulted in the colonization and replacement of mule deer mtDNA by that of white-tailed deer mtDNA...