Résumé
Behavior and genetic structure are intimately related: mating patterns and
patterns of movement between groups or populations influence the movement
of genetic variation across the landscape and from one generation to the
next. In hybrid zones, the behavior of the hybridizing taxa can also have
an important impact on the incidence and outcome of hybridization events.
Hybridization between yellow baboons and anubis baboons has been
well-documented in the Amboseli basin of Kenya, where more anubis-like
individuals tend to experience maturational and reproductive advantages.
However, it is unknown whether these advantages are reflected in the
genetic structure of populations surrounding this area. Here, we used
nuclear microsatellite genotype data to evaluate the geographic structure
and composition of baboon populations in southern Kenya, up to the border
of Tanzania. Our results indicate that, unlike for mitochondrial DNA,
microsatellite-based measures of genetic structure are in concordance with
phenotypically based taxonomic distinctions, and that the currently active
hybrid zone is relatively narrow. Interestingly, isolation with migration
analysis revealed asymmetric gene flow in this region from anubis
populations into yellow populations, in support of the anubis-biased
phenotypic advantages observed in Amboseli. Populations that are primarily
yellow but that are the recipients of anubis gene flow exhibit higher
levels of genetic diversity than yellow populations far from the
introgression front. Our results support previous work that indicates a
long history of hybridization and male-mediated genetic introgression
among East African baboons. In particular, it suggests that anubis baboons
are in the process of gradual range expansion into the historic range of
yellow baboon populations, a pattern that could be mechanistically
explained by behavioral and life history advantages that correlate with
anubis ancestry.