Search for: All records

Abstract Effective population size affects the efficacy of selection, rate of evolution by drift and neutral diversity levels. When species are subdivided into multiple populations connected by gene flow, evolutionary processes can depend on global or local effective population sizes. Theory predicts that high levels of diversity might be maintained by gene flow, even very low levels of gene flow, consistent with species long‐term effective population size, but tests of this idea are mostly lacking. Here, we show thatLycaeidesbutterfly populations maintain low contemporary (variance) effective population sizes (e.g. ~200 individuals) and thus evolve rapidly by genetic drift. However, populations harboured high levels of genetic diversity consistent with an effective population size several orders of magnitude larger. We hypothesized that the differences in the magnitude and variability of contemporary versus long‐term effective population sizes were caused by gene flow of sufficient magnitude to maintain diversity but only subtly affect evolution on generational timescales. Consistent with this hypothesis, we detected low but nontrivial gene flow among populations. Furthermore, using short‐term population‐genomic time‐series data, we documented patterns consistent with predictions from this hypothesis, including a weak but detectable excess of evolutionary change in the direction of the mean (migrant gene pool) allele frequencies across populations and consistency in the direction of allele frequency change over time. The documented decoupling of diversity levels and short‐term change by drift inLycaeideshas implications for our understanding of contemporary evolution and the maintenance of genetic variation in the wild. 

Abstract Plant–insect interactions are ubiquitous, and have been studied intensely because of their relevance to damage and pollination in agricultural plants, and to the ecology and evolution of biodiversity. Variation within species can affect the outcome of these interactions. Specific genes and chemicals that mediate these interactions have been identified, but genome‐ or metabolome‐scale studies might be necessary to better understand the ecological and evolutionary consequences of intraspecific variation for plant–insect interactions. Here, we present such a study. Specifically, we assess the consequences of genome‐wide genetic variation in the model plantMedicago truncatulaforLycaeides melissacaterpillar growth and survival (larval performance). Using a rearing experiment and a whole‐genome SNP data set (>5 million SNPs), we found that polygenic variation inM. truncatulaexplains 9%–41% of the observed variation in caterpillar growth and survival. Genetic correlations among caterpillar performance and other plant traits, including structural defences and some anonymous chemical features, suggest that multipleM. truncatulaalleles have pleiotropic effects on plant traits and caterpillar performance (or that substantial linkage disequilibrium exists among distinct loci affecting subsets of these traits). A moderate proportion of the genetic effect ofM. truncatulaalleles onL. melissaperformance can be explained by the effect of these alleles on the plant traits we measured, especially leaf toughness. Taken together, our results show that intraspecific genetic variation inM. truncatulahas a substantial effect on the successful development ofL. melissacaterpillars (i.e., on a plant–insect interaction), and further point toward traits potentially mediating this genetic effect.