Abstract
A growing body of evidence shows within-population variation in natal dispersal, but the effects of such variation on social relationships and the kin composition of groups remain poorly understood. We investigate the link between dispersal, the kin composition of groups, and proximity patterns in a population of black-and-white colobus (Colobus vellerosus) that shows variation in female dispersal. From 2006 to 2011, we collected behavioral data, demographic data, and fecal samples of 77 males and 92 females residing in eight groups at Boabeng-Fiema, Ghana. A combination of demographic data and a genetic network analysis showed that although philopatry was female-biased, only about half of the females resided in their natal groups. Only one group contained female-female dyads with higher average relatedness than randomly drawn animals of both sexes from the same group. Despite between-group variation in female dispersal and kin composition, female-female dyads in most of the study groups had higher proximity scores than randomly drawn dyads from the same group. We conclude that groups fall along a continuum from female dispersed, not kin-based, and not bonded to female philopatric, kin-based, and bonded. We found only partial support for the predicted link between dispersal, kin composition, and social relationships. In contrast to most mammals where the kin composition of groups is a good predictor of the quality of female-female relationships, this study provides further support for the notion that kinship is not necessary for the development and maintenance of social bonds in some gregarious species.
Highlights
Sex bias in natal dispersal has major implications for the evolution and expression of female-female and male-male social relationships [1], [2], [3], [4]
The social structure of C. vellerosus conformed to some of the predictions listed under hypothesis one: male-biased dispersal, female kin-based groups, and female bonded groups (Table 1)
We conclude that hypothesis three can best explain the patterns observed on a group level because groups fall on a continuum from female dispersed, not kin-based, and not bonded to female philopatric, kin-based, and bonded
Summary
Sex bias in natal dispersal has major implications for the evolution and expression of female-female and male-male social relationships [1], [2], [3], [4]. Females form strong relationships with matrilineal female kin [8], [9], [10], and they rely on kin support for acquiring and maintaining their dominance rank [11], [12], [13], [14], [15], [16]. Matrilineal kinship has a relatively small impact on male-male social relationships in these species [6]. This pattern of female philopatry, female kin-based groups, and/or strong bonds among female kin was thought to be the typical pattern among gregarious mammals, partly because early evidence of sex-bias in dispersal was limited to long-term behavioral observations of a relatively small number of species [17], [18]
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