Sociogenetic structure in a free-living nocturnal primate population: sex-specific differences in the grey mouse lemur (Microcebus murinus)

The grey mouse lemur (Microcebus murinus) has a dispersed social structure, within which female sleeping associations are common. These sleeping assoc iations have been hypothesised to confer anti-predatory and thermoregulator y benefits, especially when rearing offspring. The genetic composition of t hese associations was determined using microsatellite markers to test predi ctions derived from kin selection theory. 161 (99 males, 62 females) indivi dual M. murinus belonging to a free-living population in Ampijoroa, north-w estern Madagascar, were genotyped and observed over a total of 13 months di stributed over the dry seasons of 3 successive years (1995-1997). Kin selec tion theory predicts that these female associations should consist of close ly related members, and that female philopatry and male natal dispersal sho uld characterise the dispersal pattern within this species. These predictio ns were confirmed by the data. Five out of six female sleeping groups consi sted of one or more closely related dyads. Females that slept alone did not have close female kin in the vicinity or within the population at all. Clo sely related female dyads lived in significantly closer proximity than clos ely related male dyads and closely related male-female dyads showed interme diate proximity. In combination with the result that females possessed sign ificantly more relatives within the population than males, these findings s upport the behavioural. hypotheses of female philopatry and male natal disp ersal. Matrilinear grouping patterns and sex-biased dispersal are therefore genetically established in a dispersed primate social organisation for the first time. The results further indicate that several generations of mouse lemurs live together within a given area, implying both an effective mecha nism of kin recognition to avoid father-daughter incest and the potential f or social learning to ensure individual recognition.