Role of developmental plasticity in sexual signal divergence: a case study of cabbage white butterfly Pieris rapae signals

Abstract

Developmental plasticity can alter phenotypic development in response to changes in environmentalconditions. Recently, there is renewed interest in investigating the role of developmental plasticity in promoting divergence of sexual signals, not only because of ongoing climate change is predicted to influence sexual signaling, but also because changes in sexual signaling systems can promote signal divergence, increasing the diversity of signals. While there are examples of developmental plasticity in signals and sensory traits, few studies have examined whether such plasticity in signals and sensory traits actually translates to sexual signal divergence. Here, I use the cabbage white butterfly, Pieris rapae system to explore this idea. Cabbage whites tend to use open, brightly lit environments, but an "open niche" presents itself in the Eastern United States, where a potential novel host plant -- the invasive garlic mustard -- grows in more shady habitats. I reared cabbage white butterflies in conditions simulating open and closed light environments. Across multiple replicates of three experiments, I observed consistent and repeatable developmental plasticity in multimodal male signals, but, interestingly, inconsistent non-repeatable plasticity in female visual and olfactory sensory traits. In mating trials, females from shade-reared environments preferred males from shade-reared environments, whereas females from open environments showed no preference. This mating pattern, although asymmetric indicates that developmental plasticity can indeed act as a powerful mechanism facilitating divergence of sexual signals and could thereby contribute to early stages of population divergence and speciation by sexual selection.