EFFECT OF STRANGE MALE ODOR ON PARENTAL CARE IN LACTATING FEMALE MICE

This paper analyses the behaviour of lactating female outbred mice, Mu s musculus domesticus, in the presence of male conspecific odours. Whe n olfactory cues were left in the environment by a sexually naive adul t male, a potentially infanticidal animal, the mother took longer to r each her litter following 30 min of separation. Odours left by the sex ual partner, by an unknown male of parental status, or by a young naiv e male did not modify the mother's behaviour, compared with the contro l situation (absence of male odour). The number of ultrasonic calls of pups varied according to the characteristics of the male but did not modify the behaviour of the dam. Females took longer to reach pups on day 8 of lactation than on days 4 or 12. We suggest adaptive reasons w hy females take longer to reach pups when the situation is more risky. We tested the hypothesis that the loss of an 8-day-old litter is more expensive, in term of the mother's future reproductive success, than the loss of younger and older litters. Females conceived a new litter wit:hin a few days (the inter-birth interval varied according to the a ge of the litter previously removed) but, even though no difference in size and weight of litters was recorded, females that had the litter removed on day 8 postpartum (compared with days 4 and 12) suffered fro m a higher mortality rate in the next litter. We suggest that the time the mother takes to reach her pups in the presence of a potentially i nfanticidal male could represent a measure of parental investment. (C) 1997 The Association for the Study of Animal Behaviour.