Making eggs from nectar: the role of life history and dietary carbon turnover in butterfly reproductive resource allocation

The diets of many butterflies and moths change dramatically with development: from herbivory in the larvae to nectarivory in the adults. These diets are nutritionally distinct, and thus are likely to contribute differentially to egg manufacture. We examine the use of dietary resources in egg manufacture by four butterfly species with different patterns of oviposition and lifespan; three in the Nymphalidae (Euphydryas chalcedona, Speyeria mormonia and Heliconius charitonia), and one in the Pieridae (Colias eurytheme). Each species was fed two isotopically distinct adult diets based on sucrose, both of which differed from the larval hostplant in C-13 content. Egg isotopic composition was analyzed to quantify the contribution of carbon from the larval and adult diets to egg manufacture. In all four species, egg C-13 content increased to an asymptotic maximum with time, indicating that adult diet is an increasingly important source of egg carbon . The C-13 increase closely resembled that of a nectar-feeding hawkmoth, and was well-described by a model of carbon flow proposed for that species. This similarity suggests that the turnover from larval to adult dietary support of egg manufacture is conserved among nectar-feeding Lepidoptera. Species varied widely in the maximum % egg carbon that derives from the adult diet, from 44% in E. chalcedona to nearly 80% in S. mormonia. These differences were related both to the extent of oocyte provisioning prior to adult emergence, and to egg composition. A species' lifetime use of larval vs adult resources in egg manufacture reflected both the carbon turnover of the eggs and the timing of oviposition. Thus, the extent to which dietary resources are important in egg manufacture in butterflies depends on development (egg provisioning in teneral adults), behavior (timing of oviposition) and nutritional physiology (nutrient synthesis and turnover).