Plebejus melissa Variation

The genetic and ecological factors that shape the evolution of animal diets remain poorly understood. For herbivorous insects, the expectation has been that tradeoffs exist, such that adaptation to one host plant reduces success on other potential hosts. We investigated the genetic architecture of alternative host use by rearing individual \emph{Lycaeides melissa} butterflies from two wild populations in a crossed design on two hosts (one native and one introduced) and analyzing the genetic basis of differences in performance using genomic approaches. Survival during the experiment was highest when butterfly larvae were reared on their natal host plant, consistent with local adaptation. However, cross-host correlations in performance among families (within populations) were not different from zero. We found that \emph{L. melissa} populations possess genetic variation for larval performance, and variation in performance had a polygenic basis. We documented very few genetic variants with tradeoffs that would inherently constrain diet breadth by preventing the optimization of performance across hosts. Instead, most genetic variants that affected performance on one host had little to no effect on the other host. In total, these results suggest that genetic tradeoffs are not the primary cause of dietary specialization in \emph{L. melissa} butterflies.