The determinants of genetic diversity in butterflies

Abstract

Under the neutral theory, genetic diversity is expected to increase with population size. While comparative analyses have consistently failed to find strong relationships between census population size and genetic diversity, a recent study across animals identified a strong correlation between propagule size and genetic diversity, suggesting that r-strategists that produce many small offspring, have greater long-term population sizes. Here we compare genome-wide genetic diversity across 38 species of European butterflies (Papilionoidea), a group that shows little variation in reproductive strategy. We show that genetic diversity across butterflies varies over an order of magnitude and that this variation cannot be explained by differences in current abundance, propagule size, host or geographic range. Instead, neutral genetic diversity is negatively correlated with body size and positively with the length of the genetic map. This suggests that genetic diversity is determined both by differences in long-term population size and the effect of selection on linked sites.

Fig. 1

Neutral genetic diversity (π_4D) across European butterfly species. The phylogeny is based on 218 single-copy orthologues and rooted with the silkmoth Bombyx mori as an outgroup. All nodes have 100% bootstrap support unless marked with an asterisk (70–99%). The barplot on the right shows genome-wide estimates of π_4D for 38 focal species sampled from the six major groups of Papilionoidea present in Europe. The phylogeny explains very little of the variation in π_4D in butterflies. Source data are provided as a Source Data file

Fig. 2

The correlates of genetic diversity in butterflies. Neutral genetic diversity π_4D (a) is negatively correlated with body size and positively with the number of chromosomes (b). Source data are provided as a Source Data file