Evolution of Inbreeding Avoidance and Inbreeding Preference through Mate Choice among Interacting Relatives

While extensive population genetic theory predicts conditions favouring evolution of selffertilisation
versus outcrossing, there is no analogous theory that predicts conditions
favouring evolution of inbreeding avoidance or inbreeding preference enacted through
mate choice given obligate biparental reproduction. Multiple interacting processes complicate
the dynamics of alleles underlying such inbreeding strategies, including sexual
conflict, distributions of kinship, genetic drift, purging of mutation load, direct costs,
and restricted kin discrimination. We incorporated these processes into an individualbased
model to predict conditions where selection should increase or decrease frequencies
of alleles causing inbreeding avoidance or inbreeding preference when females or males
controlled mating. Selection for inbreeding avoidance occurred given strong inbreeding
depression when either sex chose mates, while selection for inbreeding preference occurred
given very weak inbreeding depression when females chose but never occurred when males
chose. Selection for both strategies was constrained by direct costs and restricted kin discrimination.
Purging was negligible, but allele frequencies were strongly affected by drift
in small populations, while selection for inbreeding avoidance was weak in larger populations
because inbreeding risk decreased. Therefore, while selection sometimes favoured
alleles underlying inbreeding avoidance or preference, evolution of such strategies may be
much more restricted and stochastic than is commonly presumed.