PARENTING AND POTENCY - ALTERNATIVE ROUTES TO REPRODUCTIVE SUCCESS INMALE MONGOLIAN GERBILS

Adult male Mongolian gerbils, Meriones unguiculatus, gestated in intra uterine positions between two female fetuses (2F males) are less likel y than are adult males gestated between two male fetuses (2M males) to impregnate strange female gerbils with whom they are paired. The redu ced copulatory success of 2F males is correlated with both lower circu lating levels of and reduced sensitivity to testosterone. We asked whe ther 2F male gerbils compensated for their reduced copulatory success by increasing their parental effort. 2F male gerbils engaged in less s exual activity with their mates, but were more frequently in contact w ith pups than were 2M males, huddling over the young when their mates were absent from the nest. Although there were no differences in rates of survival or growth of pups reared by pairs consisting of a female and either a 2M or 2F male, mates of 2F males delivered significantly more pups as a consequence of copulations occurring during postpartum oestrus than did either mates of 2M males or females rearing young alo ne. We interpreted these results as consistent with Ketterson & Nolan' s (1992, Am. Nat. (Supplement), 140, 533-562) hypothesis of a testoste rone-mediated trade-off between investment in sexual and parental beha viours. (C) 1997 The Association for the Study of Animal Behaviour.