Is pairing with a relative heritable? estimating female and male genetic contributions to the degree of biparental inbreeding in song sparrows (Melospiza melodia)

The degree of inbreeding expressed within populations can profoundly shape evolutionary dynamics. The degree to which individuals inbreed is frequently assumed to evolve in response to selection, for example resulting from inbreeding depression. Such evolutionary responses require additive genetic variance (VA) in the degree to which individuals inbreed. However, the magnitude of VA in the degree of biparental inbreeding has never been estimated. We devised a quantitative genetic model to estimate sex-specific VA in the degree to which individuals inbreed, while accounting for effects of individuals' own coefficients of inbreeding and genetic effects stemming from immigration. We applied this model to the degree of inbreeding expressed through social pairing in free-living song sparrows (Melospiza melodia). VA estimates for both sexes appreciably exceeded zero and the cross-sex genetic covariance was strongly positive, creating substantial total VA in the degree of inbreeding. Our analy...