Allocation of body resources to reproduction in butterflies

Sammanfattning: The life-history of an organism can be studied and understood in terms of acquisition and expenditure of resources. In butterflies, the use of resources for reproduction has been the focus of much research due to the possibility to easily quantify both the input of resources from different sources over the life-cycle as well as the partitioning of these resources to reproduction. In the first part of my thesis we studied how the pattern of partitioning of resources between somatic tissue, such as muscles, wings and exoskeleton, and storage of resources for reproductive purposes during metamorphosis affects reproduction. Theory predicts that reproduction should be strongly dependent on the relative investments in soma and reproductive reserves, but this has generally proven difficult to show empirically. Butterflies are eminently suited for testing this prediction, and our results show that fecundity of female comma butterflies (Polygonia c-album) is strongly influenced by allocation priorities. One aspect of resource use that has not attracted attention until recently is the possibility that butterflies during the reproductive stage can break down flight muscles in the thorax and use muscle nutrients for reproduction. Since butterflies are generally resource limited this could alleviate the costs resulting from somatic investment found in paper I. Through a series of studies we show that thorax mass and nitrogen content decreases over the adult lifespan in a manner consistent with the hypothesis that thorax resources are used for reproduction. In order to determine if these resources could actually come from the flight muscles, something that is known to occur in other insects, the reduction in flight muscle size over the lifespan was studied in the green-veined white butterfly (Pieris napi). The results showed that flight muscle size decreased with on average 75% in long-lived females, suggesting that breakdown of flight muscles could indeed influence reproduction. Taken together, the work in this thesis shows that resource allocation during metamorphosis strongly influences the reproductive potential, but that butterflies can overcome some of the costs of somatic investment by reallocating resources from thoracic tissue to reproduction.