Data from: 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 analyses also revealed inbreeding depression in the degree of inbreeding such that more inbred individuals paired with closer relatives, and immigrant effects such that individuals with greater genomic contributions from immigrants paired with more distant relatives. We thereby demonstrate that the degree of biparental inbreeding can show substantial VA in nature and might consequently evolve in response to selection.

种群内的近交程度可深刻塑造进化动态。学界通常认为，个体的近交程度会响应选择压力发生演化，此类选择常由近交衰退所驱动。这类演化响应要求个体近交程度存在加性遗传方差（additive genetic variance, V_A）。然而，迄今尚未有针对双亲近交程度的加性遗传方差大小的估算研究。我们构建了定量遗传模型，用以估算个体近交程度的性别特异性加性遗传方差，同时校正个体自身近交系数以及源自移民的遗传效应。我们将该模型应用于野生歌带鹀（Melospiza melodia）通过社会配对所体现的近交程度。两性的加性遗传方差估计值均显著大于零，且跨性别遗传协方差呈强正相关，使得近交程度具备可观的总加性遗传方差。我们的分析还揭示了近交衰退效应：近交程度更高的个体，其配对对象的亲缘关系更为紧密；同时发现了移民效应：携带更多移民基因组贡献的个体，其配对对象的亲缘关系更为疏远。综上，我们证实了双亲近交程度在自然种群中可具备可观的加性遗传方差，因此可能响应选择压力而发生演化。