Matrilineal kin clusters and their effect on reproductive success in the field vole Microtus agrestis

Abstract

Kin clusters of philopatric females are thought to form the basic social organization of breeding females in various vole species. The spatial association between young breeding females and their mothers was studied in five 2500-m* enclosures in natural habitats during midand late breeding season in summer 1992. The mothers (founder females) were introduced into the enclosures in die beginning of the study in June, whereas the young breeding females were born within the enclosures. Matrilineal kinship was determined by using radionudides. In July-August, 58% of young breeding females were philopatric, but 82% of the mother-daughter associations broke up until August-September. Of the young females that started to breed in August-September, only 12% were philopatric Thus the kin clusters found were short Hved and few in number during the late breeding season. The reduction in the incidence of the kin clusters coincided with an increase of population density. The mean reproductive success of females breeding in kin clusters was better than that of those breeding separately. In addition, among the nonphilopatric females there was a positive, significant correlation between reproductive success and the distance to the nearest unrelated founder female. Such correlation was not found among the philopatric females.