Pollinator loss causes rapid adaptive evolution of selfing and dramatically reduces genome-wide genetic variability

Area of Science:

• Evolutionary Biology
• Population Genetics

Background:

• Selfing populations typically have low genetic variation, which can limit evolutionary potential.
• The precise mechanisms causing this reduction in variation are not fully understood.

Purpose of the Study:

• To investigate the causes of reduced genetic variation in selfing populations.
• To understand the interplay between selection, linkage, and inbreeding on genome-wide variation.
• To assess the impact of selfing on evolutionary adaptation and the detectability of selection.

Main Methods:

• Experimental evolution of Mimulus guttatus populations over nine generations in controlled greenhouse conditions.
• Manipulation of pollinator access (bees) to induce varying levels of selfing.
• Analysis of DNA polymorphism in descendant populations.
• Computer simulations to model the effects of selection, linkage, and inbreeding on genetic variation.

Main Results:

• Populations without bees evolved increased selfing and showed significant reductions in DNA polymorphism, even with large population sizes.
• Genome-wide patterns of variation were better explained by the interaction of selection, linkage, and inbreeding than by reduced effective population size alone.
• Simulations indicated that selection on a few loci can depress neutral variation genome-wide in selfing populations, creating chromosomal heterogeneity.
• Widespread background selection was inferred in populations with bees, with only two genomic regions identified as under selection.

Conclusions:

• Large amounts of genetic drift in selfing populations compromise evolutionary potential.
• The genetic draft associated with selfing can obscure signals of selection, making outlier tests less reliable.
• Understanding these complex interactions is crucial for predicting the evolutionary trajectory of selfing species.