Sexual behavior and fertility of little mice

Male mice homozygous for the little gene mutation (lit) were originally reported to have a marked incidence of infertility. We have previously reported that these diminutive mice have normal spermatogenesis and testicular steroidogenesis. In the present study, one research goal was to determine if the reported infertility was due to a defect in male sexual behavior. Quantitative analyses of male sexual behavior of little mice and their normal siblings were completed. Natural breeding trials were also performed to reexamine the fertility of little male mice. The experimental results suggested that little mice require significantly longer times for the first mount, first intromission, and ejaculation. More importantly, the investigation provided evidence that the little mice were not infertile but that they were subfertile. The diminutive size of the little mice may be the primary etiological factor for the observed subfertility.