EvoLunch Seminar: Alec Downie (Max-Planck-Institut für evolutionäre Anthropologie)

Evolution by natural selection requires heritable variation in fitness-associated traits and produces an increase in the frequency of advantageous, trait-associated genetic variants over time.  Case studies demonstrating both phenomena remain rare in natural populations, especially for complex traits.  Furthermore, although theory predicts that polygenic adaptation ought to be the dominant mode of adaptation in nature, the vast majority of cases of adaptation observed are oligogenic.  Here, we combine phenotypic, life history, and genome resequencing data from 3,124 wild meerkats (Suricata suricatta) in the Kalahari Desert in South Africa to investigate the genomic response to selection on adult body mass.  We find that adult mass is heritable and strongly predicts lifetime reproductive success.  We show that adult mass is, as expected, a highly polygenic trait, although inbreeding allowed identification of a rare, large-effect allele.  We use gene dropping simulations through the 11-generation population pedigree to establish null expectations for allele frequency change in the absence of selection.  Over the course of the study, putative mass-increasing alleles have tended to rise in frequency relative to background expectation, consistent with adaptation in response to selection for larger size.  We therefore estimate that the genetic component of adult mass has increased by ~0.28 standard deviations in 33 years.  Surprisingly, realized adult mass has decreased over the same period.  Our results suggest that the response to selection on body mass may be a form of genetic compensation for co-occurring environmental deterioration, including increased rates of drought and extreme temperature.  Together, our results demonstrate how genomic analyses in long-term field studies can capture polygenic responses to selection in nature, even when these responses are incompletely mirrored by changes in the traits themselves.