Deconstructing early life experiences: distinguishing the contributions of prenatal and postnatal factors to adult male sexual behavior in the rat.

In rodents, a pup's experiences in utero and during postnatal development shape its sexual behavior as an adult and how it is perceived by potential mates. We show that the male rat's sexuality is primarily influenced by the postnatal sex ratio of its litter, but not by the litter's prenatal intrauterine sex ratio or the behavior of its mother. Pups from litters with differing prenatal sex ratios were divided into litters with differing postnatal sex ratios. We found that males raised in a female-biased litter exhibited less mounting than males raised in either a male-biased litter or one with an equal sex ratio, and were less attractive to sexually receptive females, eliciting fewer soliciting behaviors, such as hop-darts, and fewer lordosis behaviors. However, the number of intromissions and ejaculations did not differ across groups, which suggests that males from female-biased litters mate as efficiently as males raised in other sex ratios, but do not require as many mounts to do so. The reported differences in sexual behavior did not vary with the quality of maternal behavior or with sexual experience in adulthood.