Y-chromosome variation, dispersal and reproductive skew in bonobos and chimpanzees Linda Vigilant,1 Kevin Langergraber,1,2 and Dieter Lukas1 1Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Germany, 2Department of Anthropology, University of Michigan, Ann Arbor Abstract Dispersal is rarely observed in slowly-maturing, long-lived wild animals such as the bonobo or chimpanzee.  These apes, as well as humans, are thought to be characterized by predominantly female dispersal. Sex-linked genetic markers offer the opportunity to examine sex-specific patterns of population genetic variation.  We recently applied sex-linked (mtDNA sequence and Y-chromosome microsatellite) markers to a set of bonobos sampled from multiple locations in the wild in order to estimate the magnitude of difference in effective dispersal between the sexes and to investigate the long-term demographic history of the species.  As would be expected for a female-dispersing species, greater levels of differentiation among bonobo populations were detected using Y-chromosomal rather than mtDNA variation.  Specifically, nearly all of the Y-chromosomal variation distinguished populations, while almost all of the mtDNA variation was shared between populations.  Furthermore, genetic distance correlated with geographical distance for mtDNA but not for the Y-chromosome.  The estimate for time of the most recent common ancestor was ten times greater for mtDNA than for the Y-chromosome, while in humans the difference is only a factor of two. This suggests a more stable demographic history in bonobos as compared to humans. The quantity Nm represents the effective population size times the number of migrants per generation.  The estimate of Nm from mtDNA data was several orders of magnitude higher than that from Y-chromsome information, suggesting that female bonobos have a much higher migration rate and/or effective population size than males.  Similar results have been obtained in our recent analyses of wild chimpanzees and, to a lesser magnitude, in published studies of humans where it has been interpreted as suggesting that a history of patrilocality has shaped local and regional patterns of human genetic variation.  However, change in mobility and cultural practices in recent human history make it difficult to estimate the relative impacts of patrilocality and polygyny.  In contrast, it seems reasonable to assume that the levels of migration and reproductive skew seen in contemporary chimpanzee or bonobo groups living in the wild are typical of long-term species characteristics. Current work aims at examining the relative importance of these factors by comparing values for dispersal and reproductive skew inferred from the genetic variation data with those obtained from long-term study of bonobos and chimpanzees.