Alternative Mating Strategies in the Mongolian Gerbil

Abstract

Abstract1. In previous enclosure studies female Mongolian gerbils were found to trespass into strange territories on oestrous days and mate with the neighbouring males, although they lived in stable territorial pairs or family-groups (ÅGREN, 1976, 1983, 1984). The females mated with their social partners as well. 2. A comparable 'unfaithful' behaviour in females in oestrous was observed in a laboratory choice-test (ÅGREN & MEYERSON, 1977). 3. A mating-preference for non-siblings has been demonstrated in enclosure as well as laboratory studies (ÅGREN, 1981, 1983). 4. In the present enclosure studies four females of one family consistently trespassed in oestrous, while three females in a second family did not. Only these latter females mated within their own social group, i.e. the two daughters incestuously. 5. When two females and three males of each of these same families were placed into a new enclosure only cross family pairs formed. 6. In a laboratory experiment 12 out of 18 pairliving females gave birth to, and raised their litter, sired by a strange male, when replaced into the cage of the familiar male the day following oestrous. The cage mate was prevented from copulations by a wire-mesh during 10 days following the insemination by the strange male. These results indicate that an 'unfaithful' female may be reproductively successful. 7. The observations of the unfaithful behaviour in the females are suggestive of an alternative mating strategy to monogamy in females beneficial under high population densities. This strategy would result in avoidance of inbreeding, low migration costs, and increased chances for winter-survival.