Environmental complexity and the purging of deleterious alleles

Abstract

Sexual interactions among adults can generate selection on both males and females with genome-wide consequences. Sexual selection through males is one component of this selection that has been argued to play an important role in purging deleterious alleles. A common technique to assess the influence of sexual selection is by a comparison of experimental evolution under enforced monogamy versus polygamy. Mixed results from past studies may be due to the use of highly simplified laboratory conditions that alter the nature of sexual interactions. Here, we examine the rate of purging of 22 gene disruption mutations in experimental polygamous populations of Drosophila melanogaster in each of two mating environments: a simple, high-density environment (i.e., typical fly vials), and a lower density, more spatially complex environment. Based on past work, we expect sexual interactions in the latter environment to result in stronger selection in both sexes. Consistent with this, we find that mutations tend to be purged more quickly in populations evolving in complex environments. We discuss possible mechanisms by which environmental complexity might modulate the rate at which deleterious alleles are purged and putatively ascribe a role for sexual interactions in explaining the treatment differences in our experiment.

Spatial environmental complexity mediates sexual conflict and sexual selection in Drosophila melanogaster

“…The same two types of environmental chambers employed by Yun et al’s () assays were also used in an experimental evolution study by Singh, Agrawal, and Rundle () to see whether deleterious mutations could be more efficiently purged in more spatially complex environments. In this project, the alleles in question comprised of 22 different gene‐disruption mutations, whose frequencies were tracked over 8–10 generations of culture.…”

“…This is born out of our observation that in more complex environments, females remated less and had greater offspring production (which is consistent with the results of Yun et al, ), and there was no increase in the reproductive success of either sons or daughters produced. Thus, the more efficient purging of deleterious mutations in the spatially complex treatments of Singh et al () and Colpitts et al’s () studies is likely to be due to females of greater reproductive potential being able to realize greater fecundities under reduced male harassment (Long et al, ; Yun et al, ). However, if that is the case, what might explain the lack of differences in allele frequencies in the complex and simple environment for some of the mutations they assayed?…”

Testing for local adaptation in adult male and female fitness among populations evolved under different mate competition regimes

“…() and Singh et al. (). We refer to vials and cages as “simple” and “complex” environments but note that they differ in additional ways including volume (and hence fly density) and the availability of food and egg‐laying sites.…”

No evidence for short‐term purging benefits of sexual selection in inbred red flour beetle populations

“…Interestingly, recent studies show that the effects of sexual selection on dynamics of deleterious and beneficial genetic variants in populations may be strongly mediated by the physical structure of the environment in which mate competition and mating interactions occur (Singh et al . , Yun et al ., , ), adding another layer of complexity to the relationship between sexual selection and population performance.…”