Understanding micro-evolutionary responses of mating systems to contemporary selection requires estimating sex-specific additive genetic variances and cross-sex genetic covariances in key reproductive strategy traits. One key trait comprises the occurrence of divorce versus mate-fidelity across sequential reproductive attempts. If divorce represents an evolving behavioural strategy that responds to selection it must have non-zero individual repeatability and heritability, but quantitative estimates from wild populations are scarce. We used 39 years of individual breeding records and pedigree data from free-living song sparrows (Melospiza melodia) to quantify sex-specific permanent individual and additive genetic variances, and hence estimate repeatability and heritability, in liability for divorce. We estimated moderate repeatability among females, but little repeatability among males. Estimates of additive genetic variance were small in both sexes, and the cross-sex genetic covariance was close to zero. Consequently, the total heritability was small but likely non-zero, indicating low potential for micro-evolutionary response to selection. Rapid micro-evolutionary change of divorce rate therefore appears unlikely, even if there were substantial fitness benefits of divorce and resulting selection.
All authors were supported by a European Research Council grant to JMR. Fieldwork was supported by the Natural Sciences and Engineering Research Council of Canada and the University of British Columbia.
We thank the Tsawout and Tseycum First Nation bands for access to Mandarte, Peter Arcese, Lukas Keller, Pirmin Nietlisbach, and the University of Aberdeen Maxwell High Performance Computing cluster.
- indirect genetic effects
- mating system evolution
- social monogamy
- quantitative genetics