Abstract
A large body of theoretical work suggests that analyses of variation at the maternally inherited mitochondrial (mt)DNA and the paternally inherited non-recombining portion of the Y chromosome (NRY) are a potentially powerful way to reveal the differing migratory histories of men and women across human societies. However, the few empirical studies comparing mtDNA and NRY variation and known patterns of sex-biased migration have produced conflicting results. Here we review some methodological reasons for these inconsistencies, and take them into account to provide an unbiased characterization of mtDNA and NRY variation in chimpanzees, one of the few mammalian taxa where males routinely remain in and females typically disperse from their natal groups. We show that patterns of mtDNA and NRY variation are more strongly contrasting in patrilocal chimpanzees compared with patrilocal human societies. The chimpanzee data we present here thus provide a valuable comparative benchmark of the patterns of mtDNA and NRY variation to be expected in a society with extremely female-biased dispersal.
Highlights
Human societies show significant variation in post-marital residence practices
In addition to traditional FST based genetic differentiation estimates, we use the recently developed standardized measure of genetic differentiation [18,19]. This measure expresses genetic differentiation as the maximum amount of genetic differentiation possible given the amount of within-group variation. It allows for meaningful comparisons of genetic differentiation when the amount of within-group variation is different for mtDNA and non-recombining portion of the Y chromosome (NRY), which can result from sex, group or species differences in effective population size and in the method used to assay variation, i.e., the number and mutation rate of markers [18,19]
We found that the average NRY haplotype diversity of the four chimpanzee communities (h = 0.63, S.D. = 0.08) was significantly lower than that of the 20 patrilocal human tribes (h = 0.89, S.D. = 0.14) (Mann-Whitney U, P = 0.008, two-tailed) (Figure 1)
Summary
Human societies show significant variation in post-marital residence practices. About 70% of human societies practice some form of patrilocality, with men remaining in and women migrating from their natal household, clan, lineage, village, or other cultural unit subsumed within a larger group of people sharing a common culture and language, often termed atribe in traditional societies [1,2]. Migration outside the tribe is a rare event in traditional societies, as different tribes can have very different languages and cultures [2] By conducting their analyses at the level of tribes within a larger tribal group, rather than at the level of the household, clan, lineage or village within a tribe, these studies did not directly examine the effects of sex-biased migration on mtDNA and NRY variation. In the bonobo and hamadryas baboon studies, samples were primarily collected from unhabituated and unidentified individuals of uncertain group membership, and analyses of mtDNA and NRY variation were conducted at the broad geographic scale of the region or population [13,14] While both taxa show patterns of NRY and mtDNA variation that are consistent with patrilocality, these studies do not provide a direct link between well-characterized migration histories and contemporary patterns of genetic variation. It allows for meaningful comparisons of genetic differentiation when the amount of within-group variation is different for mtDNA and NRY, which can result from sex, group or species differences in effective population size and in the method used to assay variation, i.e., the number and mutation rate of markers [18,19]
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