Sexual motivation suppresses paternal behaviour of male gerbils during their mates’ postpartum oestrus MERTICE M. CLARK, JEANINE JOHNSON & BENNETT G. GALEF, JR Department of Psychology, McMaster University ( Received 15 August 2002; initial acceptance 12 December 2002; final acceptance 10 February 2003; MS. number: A9425) Adult male Mongolian gerbils, Meriones unguiculatus, avoid contact with their young on the day that the young are born. However, on succeeding days, fathers spend nearly as much time in contact with their offspring as do mothers. We undertook a series of studies to investigate the causes of the day-to-day change in male parental behaviour. In experiment 1, we tested males’ response to pups before, after and on the day of their mates’ parturition, and found that males were more parental both before and after the day of birth of their young than on that day. In experiment 2, we compared the parental behaviour of males paired either with intact or with ovariectomized dams (which do not come into postpartum oestrus) and found that males that were mated to intact females were less attentive to pups on the day of their birth than were the males mated to ovariectomized females. In experiment 3, we compared the parental responses of castrated and intact males to newborn pups and found that castrated males were more parental than intact males. In experiment 4, we compared the parental responses of males that were exposed to postpartum oestrous females but prevented from mating for 24 h. Extending the period of male sexual arousal to 24 h inhibited paternal responsiveness to neonates for 24 h. We interpret these results as being consistent with the hypothesis that on the day of birth of a litter, a male’s parental behaviour is inhibited by the motivation to mate during his partner’s postpartum oestrus. Ó 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. The parental activities of male and female Mongolian ger- bils, Meriones unguiculatus, are very similar (Elwood 1983), except that male gerbils do not lactate and, like males of several other rodent species (e.g. grasshopper mouse, Ony- chomys torridus: McCarty & Southwick 1977; house mouse, Mus musculus: Pristnall & Young 1978), male gerbils do not participate in care of their young until the day following their birth (Elwood 1975; Clark & Galef 1999, 2000b). This delayed onset of parental behaviour in male Mongolian gerbils does not result from females denying males access to the nest or young (Clark & Galef 2000b), as has been suggested for some other rodent species (red- backed voles, Clethrionomys gapperi: McGuire 1997; rats, Rattus norvegicus: Mennella & Moltz 1988; and, under some circumstances, meadow voles, Microtus pennsylvanicus: Storey et al. 1994). Review of videotapes of interactions of mated pairs in the hours following birth of their litter revealed no instances in which females chased or attacked their mates nor any indication that females inter- fere with males approaching the nest and young (Clark & Galef 2000b; Clark et al. 2003). In Mongolian gerbils (Norris & Adams 1981), as in many other biparental mammalian species, females are fertile following delivery of their young (prairie vole, Microtus ochrogaster: Richmond & Conway 1969; Witt et al. 1990; common marmoset, Callithrix jacchus: McNeilly et al. 1981; cottontop tamarin, Saguinus oedipus: Zeigler et al. 1987; California mouse, Peromyscus californicus: Gubernick 1988; Djungarian hamster, Phodopus campbelli: Reburn & Wynne- Edwards 1999). Consequently, on the day that the young are born, gerbil fathers must partition their reproductive effort between caring for current offspring and contributing to production of future descendents by copulating with their mates and guarding them from other males (Agren 1976, 1984, 1990; Roper & Polioudakis 1977; Agren et al. 1989). In Mongolian gerbils, the need to inseminate females on the day they give birth is particularly pressing because a male failing to impregnate his partner during her postpartum oestrus will not be able to mate with her again until after she weans her young (Meckley & Ginther 1972; Clark et al. 1990). While female gerbils are nursing the young, their vaginas remain sealed, and intromission is impossible. Furthermore, mating in gerbils is unusually Correspondence: M. M. Clark, Department of Psychology, McMaster University, Hamilton, ON L8S 4K1, Canada (email: mclark@ mcmaster.ca). 49 0003e3472/03/$30.00/0 Ó 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. ANIMAL BEHAVIOUR, 2004, 67, 49e57 doi:10.1016/j.anbehav.2003.02.006