Abstracts (first author)
Quantitative genetic covariances underlying selection on polyandry in a natural song sparrow population
Understanding the forces that drive the evolution and persistence of female polyandry remains an overarching yet elusive goal in evolutionary ecology. Many key hypotheses explaining selection on polyandry are explicitly quantitative genetic, involving genetic covariances between polyandry and fitness components in females and their offspring, and cross-sex genetic covariances with components of male fitness. However, despite recent methodological advances, these hypotheses have not previously been explicitly tested by estimating key genetic covariances in wild populations experiencing natural variation in female polyandry, male mating success and associated fitness components. I apply quantitative genetic analyses to 20 years of comprehensive paternity and pedigree data from polygynandrous song sparrows (Melospiza melodia) to test the key hypotheses that 1) there is additive genetic variance in the degrees of female polyandry and male paternity success, 2) that polyandrous females produce offspring of higher additive genetic value through extra-pair reproduction, and 3) female polyandry is positively genetically correlated with male paternity success. I demonstrate substantial additive genetic variance in both female polyandry and male paternity success, potentially allowing rapid evolution in both traits. I show that, opposite to prediction, polyandrous females produce offspring of lower additive genetic value through extra-pair reproduction, implying a component of indirect selection against polyandry. Finally, I demonstrate positive genetic covariance between female polyandry and male paternity success, but show that this covariance is constrained by genetic covariances among male fitness components. Through this explicit quantitative genetic approach I identify components of selection that could explain the evolution of polyandry and the current maintenance of genetic variation in polyandry under conflicting components of sex-specific selection.