Résumé
Inbreeding depression may be common in nature, reflecting either the
failure of inbreeding avoidance strategies or inbreeding tolerance when
avoidance is costly. The combined assessment of inbreeding risk, avoidance
and depression is therefore fundamental to evaluate the inbreeding
strategy of a population, that is how individuals respond to the risk of
inbreeding. Here, we use the demographic and genetic monitoring of 10
generations of wild grey mouse lemurs (Microcebus murinus), small primates
from Madagascar with overlapping generations, to examine their inbreeding
strategy. Grey mouse lemurs have retained ancestral mammalian traits,
including solitary lifestyle, polygynandry and male-biased dispersal, and
may therefore offer a representative example of the inbreeding strategy of
solitary mammals. The occurrence of close kin among candidate mates was
frequent in young females (~37%, most often the father) and uncommon in
young males (~6%) due to male-biased dispersal. However, close kin
consistently represented a tiny fraction of candidate mates (< 1%)
across age and sex categories. Mating biases favouring partners with
intermediate relatedness were detectable in yearling females and adult
males, possibly partly caused by avoidance of daughter–father matings.
Finally, inbreeding depression, assessed as the effect of heterozygosity
on survival, was undetectable using a capture–mark–recapture study.
Overall, these results indicate that sex-biased dispersal is a primary
inbreeding avoidance mechanism at the population level, and mating biases
represent an additional strategy that may mitigate residual inbreeding
costs at the individual level. Combined, these mechanisms explain the
rarity of inbreeding and the lack of detectable inbreeding depression in
this large, genetically diverse population.