Genetic variation in male sexual behaviour in a population of white-footed mice in relation to photoperiod.

In natural populations, genetic variation in seasonal male sexual behaviour could affect behavioural ecology and evolution. In a wild-source population of white-footed mice, Peromyscus leucopus, from Virginia, U.S.A., males experiencing short photoperiod show high levels of genetic variation in reproductive organ mass and neuroendocrine traits related to fertility. We tested whether males from two divergent selection lines, one that strongly suppresses fertility under short photoperiod (responder) and one that weakly suppresses fertility under short photoperiod (nonresponder), also differ in photoperiod-dependent sexual behaviour and responses to female olfactory cues. Under short, but not long, photoperiod, there were significant differences between responder and nonresponder males in sexual behaviour and likelihood of inseminating a female. Males that were severely oligospermic or azoospermic under short photoperiod failed to display sexual behaviour in response to an ovariectomized and hormonally primed receptive female. However, on the day following testing, females were positive for spermatozoa only when paired with a male having a sperm count in the normal range for males under long photoperiod. Males from the nonresponder line showed accelerated reproductive development under short photoperiod in response to urine-soiled bedding from females, but males from the responder line did not. The results indicate genetic variation in sexual behaviour that is expressed under short, but not long, photoperiod, and indicate a potential link between heritable neuroendocrine variation and male sexual behaviour. In winter in a natural population, this heritable behavioural variation could affect fitness, seasonal life history trade-offs and population growth.