Diet quality and plastic melanism in a caterpillar

Pigmentation in animals is often based on availability of dietary precursors. When precursors are limited, pigmentation may be associated with resource allocation trade-offs. Many insects show intraspecific variation in melanism, however, little work has investigated the dietary basis of this variation. Unlike the well-studied carotenoids, melanin can be produced de novo in animals, but the precursors of the melanin biosynthesis pathway (the amino acids phenylalanine and tyrosine) are only derived from the diet. Furthermore, phenylalanine and tyrosine are components of flight muscle and vitellogenin, the major egg protein, which may result in melanin-based trade-offs with flight and fecundity. Such pigmentation trade-offs have received very little attention in melanin. In this study we ask how diet composition influences larval cuticular melanism in Hyles lineata (Sphingidae), which are known to be highly variable in their pigmentation. We will raise larvae in the lab under conditions known to induce melanism in this species (low temperature and short photoperiod). Larvae will be raised on diets differing in their amount of tyrosine and phenylalanine but similar in overall macronutrients. We will quantify melanism in the 3^rd-5^th instars using digital image analysis. We will test whether melanin-based trade-offs occur by measuring adult investment into flight and reproduction. Investment will be quantified by measuring caloric allocation to the abdomen and thorax with bomb calorimetry. This study will highlight the importance of specific micronutrients on dynamics of allocation trade-offs across life stages.