Sexual selection in males, but not females, purges the standing genetic load in a seed beetle

• The concept of genic capture revealing the genetic quality in males is central to sexual selection theory and the potential for males to purge a population’s weakly deleterious partially recessive mutation load. However, empirical demonstrations of sexual selection in males purging the standing genetic load on a population are almost completely lacking, perhaps in part because of the partially hidden/recessive nature of mutation load limiting its detection. Here, we exposed mutation load by experimentally increasing homozygosity in 16 strains of the seed beetle Callosobruchus maculatus isolated from a natural population. We then assessed the potential for selection to purge load in males and females separately by correlating the breeding values for variance in competitive lifetime reproductive success (i.e. fitness) among the outbred combinations of those strains with the difference between outbred and inbred breeding values for fitness (i.e. mutation load), in a way that avoided correlating confounded variables. Outbred breeding values for male fitness were significantly negatively correlated with mutation load, demonstrating the ability of males to purge mutation load. Breeding values for female fitness, however, were uncorrelated to mutation load, likely because female fitness did not vary enough to reflect genetic quality. Thus, our results are consistent with an additional value to sexual reproduction beyond recombination: whereas females experience relatively weak selection, limiting purging of their own mutation load, this may be achieved by producing males and having them compete intensely for access to their eggs, such that only those of high genetic quality contribute to the next generation. These results have important implications for our understanding of sexual selection, the maintenance of variation in fitness-related traits, and the prevalence of sexual reproduction.

Nyckelord

Biologi med inriktning mot zooekologi

Biology with specialization in Animal Ecology

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vet (ämneskategori)

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