Plastic and evolutionary responses of butterflies to climate variability and climate change
How phenotypes respond to changing environments is a key open question in ecology and evolutionary biology. To forecast responses to future change, we need to understand both the mechanisms underlying responses, and the aspects of the environment to which phenotypes respond. Here, we explore these areas using case studies of butterfly responses to global change. We first explore how a complex phenotype, the timing of life cycle events (phenology), responds to climate change along gradients of land-use change; we focus on an assemblage of twenty butterfly species across the state of Ohio, USA. We then further explore how environmental context mediates evolutionary responses in a key thermoregulatory trait, melanin, to recent climate change among alpine and subalpine populations of the butterfly Colias meadii.
Several patterns emerged from the two case studies. In both studies, environmental context—the degree of land-use change in the Ohio butterfly assemblage and elevation in C. meadii—impacted the response to climate change. Nearly half of the Ohio butterfly species assemblage exhibited phenological delays (potentially indicative of a stress response) in relatively extreme environments with warming from both climate and land-use change, but exhibited more typical responses of phenological advancement in environments with either warming due to climate change or warming due to land-use change alone. Mechanistically, this suggests an important role for non-additive effects of multiple sources of environmental change on plasticity in phenology across a large fraction of the butterfly assemblage. Similarly, in C. meadii the predicted evolutionary response in wing melanin to recent climate change depends on where the population occurs within the elevational range of the species. At the subalpine site, despite substantial interannual variation in the predicted magnitude and direction of selection, predicted directional selection on wing absorptivity has shifted from predominantly positive selection for increased melanism to negative selection on this trait over the past 60 years. In contrast, at the alpine site, although the magnitude of directional selection has decreased over this timeframe, selection has been predominantly positive (for increased melanism). Together, these results further support the idea that quantifying relevant environmental attributes and identifying the mechanisms underlying responses are essential to forecast responses to future environmental change.