Reproductive expenditure affects utilization of thoracic and abdominal resources in male Pieris napi butterflies

1. One route to a deeper understanding of the life history of organisms is to identify how resources are acquired and used for reproduction. This may be particularly relevant for insects such as nectar-feeding butterflies, which change diets during the life cycle. 2. Nitrogenous resources used for reproduction in nectar-feeding butterflies come principally from the juvenile diet and are stored in abdominal reserves. Juvenile resources are also used to build the soma of the adult. Consequently somatic and reproductive investment will trade off and constrain the amount of resources available for egg and spermatophore production. Recent findings show a pronounced decrease in thorax resource content and suggest that nitrogen from somatic tissue can be reallocated to reproduction and thus alleviate the resource limitation upon reproduction. 3. In this paper we test the prediction that the observed decrease in thorax nitrogen content is related to the expenditure of resources in spermatophore production in Pieris napi males. By comparing thorax nitrogen content over the life span between males mated 0-3 times, we show that mating history is an important factor in explaining the observed decrease in nitrogen content. 4. These results support the hypothesis that thoracic resources are used for reproduction in male nectar-feeding butterflies.