Potential for female kin associations in wild western gorillas despite female dispersal

Abstract

Female philopatry and male dispersal are the norm for most mammals, and females that remain in their natal region often derive foraging or social benefits from proximity to female kin. However, other factors, such as constraints on group size or a shortage of potential mates, may promote female dispersal even when female kin associations would be beneficial. In these cases, female kin associations might develop, not through female philopatry, but through female emigration to the same group. To date, little attention has been focused on the potential for kin-biased behaviour between females in female-dispersing species. Here we investigate the genetic relationships among adults in eight wild groups of unhabituated western gorillas (Gorilla gorilla) at the Mondika Research Center using microsatellite genotyping of DNA collected from hair and faeces. We found that almost half (40%) of adult females had an adult female relative in the same group and average within-group relatedness among females was significantly higher than that expected under a model of random dispersal. This provides the first genetic evidence that females can maintain social associations with female relatives in spite of routine natal and secondary dispersal. In addition, we show that females appear to avoid related silverback males when making dispersal decisions, suggesting that a strategy of non-random female dispersal may also function to avoid inbreeding.

Figure 1

Minimum patterns of dyadic relatedness among adults in eight groups of western gorillas. Circles labelled with letters represent nesting sites of different social groups. Leaf symbols indicate nests that yielded insufficient DNA for analysis. The overall fraction of nests typed is noted under each nest site. Known breeding females are shaded; other females are of unknown breeding status. Dyads connected by lines were identified as related. Thin lines indicate that the dyad can be excluded as a parent–offspring pair. Position does not reflect relative location within the study site, but most groups are likely to have adjacent or overlapping home ranges.