Comparative studies on ovary and serum hormone levels in silver and blue foxes and their hybrids.

The silver and blue fox appear closely related despite their belonging to different genera, and the male and female fox hybrids are completely sterile in mating inter se or back to either of the parental groups. In the present study, we compared ovarian morphology and serum hormone concentrations among silver foxes, blue foxes, HSBs (silver fox male × blue fox female hybrids) and HBSs (blue fox male × silver fox female hybrids) during the pre-breeding and the breeding period. We found that either the fertile blue and silver foxes or the infertile hybrid foxes showed typical characteristics of ovary, with primordial, primary, secondary, antral and Graafian follicles.

Identification of key genes associated with spermatogenesis arrest in fox hybrids using weighted gene co-expression network analysis.

The silver fox and the blue fox represent different genera, but produce viable offspring. Although these hybrids show obvious heterosis, they are completely sterile due to spermatogenic arrest at the early stages of spermatogenesis, especially mitosis and meiosis I; the hybrids produce few spermatogonia and primary spermatocytes, and no secondary spermatocytes. Although the mechanisms of spermatogenic arrest have been well investigated, transcriptomic differences between hybrid and the pure-species testes have not clarified.