231T Poster - Population Genetics
Thursday June 09, 9:15 PM - 10:00 PM

Authors:
Mariana Harris ¹; Nandita Garud ^2,3

Affiliations:
1) Department of Computational Medicine, University of California, Los Angeles, Los Angeles, CA; 2) Department of Human Genetics, University of California, Los Angeles, Los Angeles, CA; 3) Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, CA

Keywords:
Natural selection

Adaptation on the X chromosome has attracted significant interest from evolutionary biologists because its dynamics seem to be distinct from that of autosomes. The X chromosome is hemizygous in males, leaving it fully exposed one third of the time to the effects of natural selection and, thus, potentially subject to different evolutionary dynamics than autosomes. Here, we investigate the differences in the mode and tempo of adaptation in the X chromosome and autosomes. Specifically, we test the hypothesis that hard sweeps, in which a single adaptive mutation rises to high frequency, are more common on the X chromosome due to there being a smaller effective population size and a reduction in standing genetic variation resulting from more efficient selection. By contrast, we predict that soft sweeps, in which multiple haplotypes rise to high frequency simultaneously, are more common on the autosomes. We quantify the incidence of hard versus soft sweeps in North American D. melanogaster population genomic data with haplotype homozygosity statistics and find an enrichment of hard sweeps on the X chromosome relative to the autosomes, confirming predictions we make from simulations. This suggests that signatures of selection may differ between the X chromosome and the autosomes in D. melanogaster. Understanding these differences may enable a deeper understanding of how important phenotypes arise as well as the impact of fundamental evolutionary parameters on adaptation, such as dominance, sex-specific selection, and sex-biased demography.