Observations on spermatogenesis, sperm phenotype, and fertility in white-tailed × mule deer hybrids and a yak × cow hybrid

Abstract

Fertility, spermatogenesis, and sperm phenotype were investigated in three hybrid deer (Odocoileus virginianus dacotensis × Odocoileus hemionus hemionus) and a yak × domestic cow hybrid (Bos mutus (grunniens) × Bos primigenius (taurus)) using histological techniques. All of the hybrids studied were infertile but varied in the degree of testicular differentiation, spermatogenic activity, and sperm production. The hybrid yak was the least developed and the white-tailed deer × F 1 hybrid was the most advanced. F 1 backcrossing improved spermatogenesis, output, and morphology of sperm, but not the fertility of the donor, indicating that normal sperm morphology alone does not assure fertility. Two deer hybrids that produced sperm differed in sperm phenotype from each other and from the parental species. Interaction of a Y chromosome from one species and autosomal sex-determining genes from the other species is suggested as a possible explanation of sterility in male hybrids.