POLYCOLOR NUTRITION · Nutritional ecology and seasonal colour polymorphism in a butterfly

Large colour ornaments such as bright plumage in birds or vivid wing coloration in butterflies are some of the most intriguing phenomena in the natural kingdom. However, the selective pressures and constraints involved in the evolution of these traits are in most cases poorly understood. Here we posit that evaluating the underlying nutritional demands of large colour patterns promises to provide novel insights in to the evolution of colour traits. Colour patterns can represent surprisingly large pools of specific nutrients. For example, male Cabbage White butterflies (Pieris rapae) invest as much as 15% of their total adult nitrogen in wing pigmentation alone. However, despite the substantial resource draw that many colour patterns impose on their bearers and the potential importance of these resource demands to other morphological and life history traits, the nutrient dynamics underlying production of colour traits have rarely been considered in studies of their evolution. We will evaluate the importance of nutrient ecology in the evolution of the distinct seasonal colour forms of the European Map Butterfly, Araschnia levana. This butterfly exhibits an orange, ommochrome-dominated spring form and a black-and-white, melanin-dominated summer form. These two colour forms differ substantially in the nutrient demands they impose, with the former requiring large amounts of tryptophan, whereas the latter requires large amounts of phenylalanine and/or tyrosine. In order to better understand the evolution of this colour polymorphism, we will evaluate seasonal differences in nutrient availability, acquisition and allocation. We will also explore the role of hormonal control in mediating nutrient-based life history tradeoffs associated with these two distinct colour phenotypes. We expect that synthesis of results from the proposed studies will allow us to more thoroughly understand the evolution of this colour polymorphism, and colour traits more generally.