Promiscuity occurs when males and females in a population mate randomly and with multiple partners. In general, the theory of mating systems suggests that promiscuity should be rare or absent in animals, as it is usually to the advantage of one or both of the genders to choose their mates. Promiscuity might occur in species in which the environment is completely unpredictable--in which it is impossible to judge which mate might carry genes that would be good in the next generation. Another factor favoring promiscuity would be the inability of any animal to hold a territory and monopolize access to critical resources.
Mere observation of seemingly random matings does not establish that a mating system is, in fact, promiscuous. Copulation can serve social functions other than reproduction such as bonding, dominance, or even concealment of actual paternity of a female's offspring. Genetic studies (usually using DNA fingerprinting or microsatellite marker techniques) establish true paternity of juveniles. If the norm for males in a population is to sire offspring with more than one female, and each of the males is more or less equally succesful in fathering young, then the mating system is truly promiscuous. If there is substantial variation among males in their success in siring young, then even if mating frequencies suggest promiscuity, the system is probably actually polygynous.
The snowshoe hare, Lepus americanus, is best known for its dramatic population cycles in Canada. Snowshoe hare populations rise and fall on a ten-year cycle.While once thought to represent a classical predator-prey cycle, it is now recognized that hare population cycles are more complex, regulated not only by predators but also by food supply (Krebs et al. 1995). Snowshoe hares show no sign of being territorial, or of having any sort of complex social system, even at the peak of their population cycle.
Going along with this lack of social complexity is a promiscuous mating system. Behavioral observations suggest that female and male snowshoe hares mate with many partners, and genetic analyses confirm that in many litters more than one father is represented. Some males, though, fathered more offspring by being able to be the only father of some litters. Burton (2002) interprets these results to indicate that the mating system is not fully promiscuous, in that paternity is not entirely random. Some sort of competition may occur among males (perhaps some males are more attractive to females and gain more matings). The number of fathers represented in the offspring, and the frequency of litters representing more than one father does make this mating system as close to true promiscuity as has been observed in any mammal.
This hare was photographed in the Colorado subalpine. It shows its summer coloration, which blends well with the litter of pine needles and twigs on the ground. In winter, this animal will be entirely white.
Burton C 2002 Microsatellite analysis of multiple paternity and male reproductive success in the promiscuous snowshoe hare. CANADIAN JOURNAL OF ZOOLOGY-REVUE CANADIENNE DE ZOOLOGIE 80 (11): 1948-1956
Krebs C J, Boutin S, Boonstra R, Sinclair A R E, Smith J N M, Dale M R T, Martin K, Turkington R 1995 Impact of food and predation on the snowshoe hare cycle SCIENCE 269 (5227): 1112-1115
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