Facultative promiscuity in a presumably monogamous mouse Apodemus microps

Promiscuity and monogamy are two extremes of fitness optimisation. Direct evidence for both extremes is documented in numerous studies where a measure of promiscuity/monogamy is often the number of fathers in individual litters using, for example, fragment analysis of highly polymorphic microsatellite loci. In this study, five known polymorphic microsatellite loci were used to assess biological parentage of 174 embryos of 24 pregnant females from a natural Czech population of pygmy field-mice Apodemus microps Kratochvil et Rosicky, 1952. The results revealed that the majority (67%) of litters were fathered by single males. However, there was a trend showing that the number of males successively (but not significantly) increased during the season, thus suggesting that monogamy in the pygmy field mouse is not obligatory but may depend on a population density and habitat type.