Oviposition and microhabitat selection in a butterfly under niche expansion : testing the role of behaviroual plasticity and learning by Simon Braem

Plasticity in biological traits is assumed crucial for allowing organisms to cope with heterogeneity of ecological resources in time and space. It is still unclear to what extent different types of plasticity may affect adaptive behaviours to colonize and thrive in landscapes under human-induced rapid environmental change. In this PhD-project, this issue is addressed by studying oviposition behaviour in the Speckled wood (Pararge aegeria). This butterfly used to be a forest (edge) species, but recently colonized anthropogenic, non-forested areas too. It is a case of ecological niche expansion. By using both experimental findings and insights from the literature, we first explored the function of microclimatic preferences during oviposition site selection in P. aegeria and other Lepidoptera. Species interact differently with different spatial scales of microclimatic variation, which affects the performance of their offspring in various ways. Next, we tested to what extent microclimatic conditions for larvae differed among forest, agricultural and urban landscapes. We provide a detailed picture of the distribution of microclimatic conditions in forest habitats and how they differ from agricultural and urban habitats. For the main research question about oviposition, we used lab-reared F1-offspring from wild-caught females of populations of both forest and agricultural ecotypes. Through a reciprocal transplant set-up, larvae developed under either canopy-covered or open field conditions. Emerging individuals were tested for effects of ecotype, developmental background and adult experience on oviposition search behaviour and oviposition site selection. Our experiments show that different drivers have different effects on specific oviposition-related traits: motivation to oviposit was mostly affected by larval experience, whereas search effort and exploration decisions by ecotype origin. These effects interacted with perceived patch quality as simulated in the cage environment. Ecotype and early experience effects were largely overruled by adult female experience. Several pre-adaptations have contributed to the recent colonisation success of P. aegeria in North-Western Europe, including females being well adapted to find (and learn to find) hygrothermally buffered egg-laying sites. Eco-evolutionary processes like local adaptation and non-random spatial sorting likely explain some of the ecotype-related differences. Our results inform on mechanisms of learning and on what this means for our understanding of the evolution of learning in insects in changing environments. The functional relevance of learning is strongly associated with the behavioural trait that is measured and the ecological relevance of the experimental conditions.