Molecular analysis reveals tighter social regulation of immigration in patrilocal populations than in matrilocal populations

Abstract

Human social organization can deeply affect levels of genetic diversity. This fact implies that genetic information can be used to study social structures, which is the basis of ethnogenetics. Recently, methods have been developed to extract this information from genetic data gathered from subdivided populations that have gone through recent spatial expansions, which is typical of most human populations. Here, we perform a Bayesian analysis of mitochondrial and Y chromosome diversity in three matrilocal and three patrilocal groups from northern Thailand to infer the number of males and females arriving in these populations each generation and to estimate the age of their range expansion. We find that the number of male immigrants is 8 times smaller in patrilocal populations than in matrilocal populations, whereas women move 2.5 times more in patrilocal populations than in matrilocal populations. In addition to providing genetic quantification of sex-specific dispersal rates in human populations, we show that although men and women are exchanged at a similar rate between matrilocal populations, there are far fewer men than women moving into patrilocal populations. This finding is compatible with the hypothesis that men are strictly controlling male immigration and promoting female immigration in patrilocal populations and that immigration is much less regulated in matrilocal populations.ethnogenetics ͉ human evolution ͉ sex-bias dispersal G enetic analyses have supported the existence of sex-biased gene flow in various human populations (1-4). Several studies have shown that women could move among populations at higher rates than men (5-8), potentially explaining lower levels of local differentiation for mtDNA than Y chromosome markers (e.g., 9, 10), even though a recent analysis revealed similar levels of genetic structure at a broader scale (11). Different forms of social organization can impact patterns and levels of genetic diversity (12, 13), and sex differences in postmarital residence choice have been proposed to greatly affect isolation by distance patterns in humans (6). The patterns of gender-specific genetic markers, such as mitochondrial and Y chromosome diversity, were recently found to be deeply affected by postmarital residence choice in six populations of northern Thailand (14). Patrilocal populations, where men remain in their natal village and women move to their husband's village, showed lower levels of Y chromosome diversity than matrilocal populations; the reverse situation was observed for mtDNA diversity. Moreover, genetic distances were found to be lower for mtDNA between patrilocal populations than between matrilocal populations, a situation that was reversed for Y chromosome markers (14). Although these results strongly supported the view that sex-biased dispersal shaped patterns of diversity within and between populations, no attempt was made to quantify and compare the movement of males and females in the two types of societies. Such quantitation may yield additional insights into cult...

Larger mitochondrial DNA than Y-chromosome differences between matrilocal and patrilocal groups from Sumatra

“…Thus, previous studies that analysed only a portion of the mtDNA genome and failed to find a difference relating to matrilocality versus patrilocality may have lacked sufficient resolution. Overall, our results confirm the idea that cultural practices can influence genetic variation 34 , but also demonstrate that the expected influence of matrilocality and patrilocality on genetic diversity may not always hold; in particular, in the present case, matrilocality seems more tightly regulated than patrilocality, in contrast to previous results 4 .…”

“…These results are surprising, as other studies have shown that, in general, there is more structure within human populations for Y-chromosome diversity than for mtDNA, which is likely to reflect the high global prevalence of patrilocality 1,5 . Furthermore, patrilocal practises seem to be more tightly regulated than matrilocal practices 4 , resulting in a higher female than male migration rate 2,[26][27][28] . Perhaps matrilocality has been more tightly regulated in the Semende, and patrilocality less tightly regulated in the Besemah, than has been observed previously.…”

“…An obvious test of this hypothesis is that the genetic differences among matrilocal groups should then be larger for mtDNA than for the NRY and that the mtDNA diversity is lower in matrilocal groups than patrilocal. Indeed, this prediction was fulfilled in the first comparison of patterns of mtDNA and NRY variation in matrilocal and patrilocal groups, among the hill tribes of Thailand 4,6 . However, a subsequent study of matrilocal and patrilocal groups in India failed to find the predicted patterns of mtDNA versus NRY diversity 7 , whereas another study has called into question the original observation of larger differences among human groups in general for the NRY versus mtDNA 8 .…”

“…Genetic differences between human populations are usually larger for non-recombining regions of the Y-chromosome (NRY) than for mitochondrial DNA (mtDNA) [1][2][3] , and this pattern has been attributed to higher female than male migration due to patrilocality 1,4 , which is typical for about 70% of human societies 5 . Higher female than male migration results in a larger effective population size for females than males, which in turn predicts increased mtDNA and decreased Y-chromosome diversity within groups, and larger differences between groups for the Y-chromosome than for mtDNA.…”

Inferring Past Demography Using Spatially Explicit Population Genetic Models

“…This was probably a result of a lack of appropriate data sets, lack of computational power, and lack of tools to automate ABC inference. Our team has applied these techniques in the context of human evolution and ethology (Fagundes et al 2007;Hamilton et al 2005b). Concerning the ethology application (Hamilton et al 2005b), we have analyzed patterns of mitochondrial and Y-chromosome diversity in three matrilocal and three patrilocal groups from northern Thailand to infer by means of ABC the number of males and females arriving each generation in these populations and to estimate the age of their range expansion.…”