Sociogenetic structures, dispersal and the risk of inbreeding in a small nocturnal lemur, the golden-brown mouse lemur (Microcebus ravelobensis)

Natal dispersal reduces the risk of inbreeding, since it is typically biased towards one sex. Golden-brown mouse lemurs (Microcebus ravelobensis) form mixed-sex sleeping groups whose genetic composition is not yet known. This study investigates the composition of eight sleeping groups and the dispersal pattern in a free-living population of this nocturnal primate. Genetic relatedness and parentage was calculated for 101 individuals (43 males, 58 females) based on microsatellite analyses. Matrilinear relatedness played a major role in the composition of sleeping groups. Co-sleepers were significantly more closely related than members of different sleeping groups. Dispersal was not strongly biased towards one sex. More than 50% of all potential sons (N = 19) and daughters (N = 26) remained in their natal range well into their first mating season, but potential sons disappeared more frequently than daughters lateron. These data indicate that many sons may have delayed their dispersal. This delayed dispersal may have increased the risk of inbreeding, since closely related males and females stayed within one home range diameter of each other quite regularly in the mating season. In fact, two definite cases of inbreeding were detected. The likely benefits of delayed dispersal are discussed in view of the confirmed cases of inbreeding.