Effects of Genetic Drift and Gene Flow on the Selective Maintenance of Genetic Variation

Abstract

Explanations for the genetic variation ubiquitous in natural populations are often classified by the population-genetic processes they emphasize: natural selection or mutation and genetic drift. Here we investigate models that incorporate all three processes in a spatially structured population, using what we call a construction approach, simulating finite populations under selection that are bombarded with a steady stream of novel mutations. As expected, the amount of genetic variation compared to previous models that ignored the stochastic effects of drift was reduced, especially for smaller populations and when spatial structure was most profound. By contrast, however, for higher levels of gene flow and larger population sizes, the amount of genetic variation found after many generations was greater than that in simulations without drift. This increased amount of genetic variation is due to the introduction of slightly deleterious alleles by genetic drift and this process is more efficient when migration load is higher. The incorporation of genetic drift also selects for fitness sets that exhibit allele-frequency equilibria with larger domains of attraction: they are "more stable." Moreover, the finiteness of populations strongly influences levels of local adaptation, selection strength, and the proportion of allele-frequency vectors that can be distinguished from the neutral expectation.

Localized environmental heterogeneity drives the population differentiation of two endangered and endemic Opisthopappus Shih species

“…The many gullies and gorges of the Taihang Mountains likely prevented pollen exchange between populations (being a wind-pollinator species). With the decline in genetic exchange, population divergence would increase [52,53]. Moreover, the environments (including temperature and precipitation) for each population was diversified due to the variable localized climates of the Taihang Mountains.…”

The Maintenance of Single-Locus Polymorphism by Maternal Selection

“…The relatively even allele frequencies found using both parameter-space and constructionist approaches ( Figure 6 ) is in contrast to that under constant viability selection ( Spencer and Marks 1988 ). In finite populations, genetic drift is likely to reduce the number of alleles in the standing variation ( Star and Spencer 2013 ). Everything else being equal, even equilibrium allele frequencies will be more resistant to extinction due to genetic drift and so maternal selection may play a more important role in maintaining variation in smaller populations than our results might, at first, suggest.…”

Environmental and anthropogenic drivers of connectivity patterns: A basis for prioritizing conservation efforts for threatened populations

“…Genetic diversity, as determined by gene flow, stochastic genetic drift and/or selection, allows natural populations to adapt to local conditions (Gandon & Nuismer, ; North, Pennanen, Ovaskainen, & Laine, ). Genetic variation and gene flow are higher in large populations that typically accumulate more mutations than smaller ones (Star & Spencer, ). In vulnerable and small caribou populations, the consequences of drift and restricted gene flow are more profound as they are suspected to decrease genetic variation and enhance isolation, respectively (Serrouya et al., ; Weckworth et al., ).…”