Does sexual trait expression reflect adaptation in a wild insect?

Abstract Sexual selection has the potential to accelerate adaption if males that are better adapted to the environment are more likely to mate. This requires that a male’s degree of environmental adaptation is reflected in his expression of secondary sexual traits. To test this hypothesis, we created a population of crickets in a meadow in N. Spain where half of the individuals were expected to be well adapted to the local environment and half poorly adapted. We achieved this by replacing all the crickets in the natural population with individuals derived from replicate independent source populations. Half of the introduced crickets had parents from low altitude environments similar to the experimental meadow. The other half had parents from high altitude environments to which genetic adaptation in traits has previously been identified. After tagging every adult, we observed the lives of these common-garden-reared and either genetically well-adapted or poorly-adapted individuals. Using video from a network of 140 day/night cameras we were able to quantify sexual trait expression, mating success, lifespan and developmental timing. We observed differences between crickets from high and low altitudes in the date that they reached adulthood according to where they were reared. There were also complex interactions between genetic background, rearing environment and trait expression that affected mating success. However, contrary to the theory, we did not find any convincing evidence for differences in sexual trait expression between well adapted and poorly adapted males.