The hidden matrilineal structure of a solitary lemur: implications for primate social evolution.

Kin selection affects many aspects of social behaviour, especially in gregarious animals in which relatives are permanently associated. In most group-living primates with complex social behaviour, females are philopatric and organized into matrilines. Models of primate social evolution assume that females in solitary primates are also organized into matrilines. We examined the genetic structure and the mating system of a population of Coquerel's dwarf lemur (Mirza coquereli), a solitary primate from Madagascar, to test this assumption. Our genetic and behavioural analyses revealed that this population of solitary individuals is indeed structured into matrilines, even though this pattern was not predicted by behavioural data. Specifically, females sharing a mitochondrial DNA haplotype were significantly clustered in space and the average genetic and geographical distances among them were negatively correlated. Not all females were philopatric, but there is no evidence for the successful settlement of dispersing females. Although not all adult males dispersed from their natal range, they were not significantly clustered in space and all of them roamed widely in search of oestrous females. As a result, paternity was widely spread among males and mixed paternities existed, indicating that scramble competition polygyny is the mating system of this species. Our data therefore revealed facultative dispersal in both sexes with a strong bias towards female philopatry in this primitive primate. We further conclude that complex kinship structures also exist in non-gregarious species, where their consequences for social behaviour are not obvious.