No evidence for female kin association, indications for extragroup paternity, and sex‐biased dispersal patterns in wild western gorillas

Characterizing animal dispersal patterns and the rational behind
individuals’ transfer choices is a long-standing question of interest in
evolutionary biology. In wild western gorillas (Gorilla gorilla), a
one-male polygynous species, previous genetic findings suggested that,
when dispersing, females might favor groups with female kin to promote
cooperation, resulting in higher-than-expected within-group female
relatedness. The extent of male dispersal remains unclear with studies
showing conflicting results. To investigate male and female dispersal
patterns and extra-group paternity, we analyzed long-term field
observations, including female spatial proximity data, together with
genetic data (10 autosomal microsatellites) on individuals from a unique
set of four habituated western gorilla groups, and four additional
extra-group males (49 individuals in total). The majority of offspring (25
of 27) were sired by the group male. For two offspring, evidence for
extra-group paternity was found. Contrarily to previous findings, adult
females were not significantly more related within groups than across
groups. Consistently, adult female relatedness within groups did not
correlate with their spatial proximity inferred from behavioral data.
Adult females were similarly related to adult males from their group than
from other groups. Using RST statistics, we found significant genetic
structure and a pattern of isolation by distance, indicating limited
dispersal in this species. Comparing relatedness among females and among
males revealed that males disperse farer than females, as expected in a
polygamous species. Our study on habituated western gorillas shed light on
the dispersal dynamics and reproductive behavior of this polygynous
species and challenge some of the previous results based on unhabituated
groups.