Genetic divergence and phenotypic plasticity contribute to variation in cuticular hydrocarbons in the seaweed fly C. frigida

Abstract

Male sexual signals facilitate female choice and thereby reduce mating costs. The seaweed fly Coelopa frigida is characterized by intense sexual conflict, yet it is unclear which traits are under sexual selection. In this study, we investigated phenotypic and genetic variation in cuticular hydrocarbons (CHCs) in C. frigida for the first time. CHCs are ubiquitous in insects and they act as sex pheromone in many dipterans. We characterized CHCs and found that composition was affected by both genetic (sex and population origin) and environmental (larval diet) factors. We identified general shifts in CHC chemistry as well as individual compounds and found that the methylated compounds, mean chain length, proportion of alkenes, and normalized total CHCs differed between sexes and populations. We combined this data with whole genome resequencing data to examine the genetic underpinnings of these differences. We identified 11 genes related to CHC synthesis and found population level outlier SNPs in 5 that are concordant with phenotypic differences. Together these results reveal that the CHC composition of C. frigida is dynamic, strongly affected by the larval environment, and likely under natural and/or sexual selection.