Nuptial gifts, resource budgets, and reproductive output in a polyandrous butterfly

Many female insects receive material during mating, referred to as "nuptial gifts," that may increase the female's resource budget. This investigation examines how nuptial gifts influence female nitrogen and carbon budgets in a polyandrous butterfly, Pieris napi. During mating, a virgin male of this species transfers a large and nutritious ejaculate containing 14% nitrogen by dry mass. The amount of nitrogen transferred is equivalent to that in si milar to 70 eggs. Females use the male-transferred nutrients to increase th eir pool of nutrients used for egg production and show a positive relations hip between amount of ejaculate material received and lifetime reproductive output. It is clear that for multiply mated females, nitrogen derived from male nuptial gifts is essential for a balanced nitrogen budget. As in earl ier studies, female thorax mass decreased with age, indicating that old fem ales of P. napi are able to use more of the resources from their thorax tha n young females. Since male-transferred material also increases female long evity, multiply mated females also use more of their resources from the tho rax. Consequently, multiply mated females have a relatively higher reproduc tive investment than singly mated females, i.e., they transform a larger pa rt of their body reserves to egg production. These results are important fo r studies that involve male-transferred nutrients in female life history pa tterns as well as for investigations of links between nuptial gifts and sex ual selection theory. When the value of nuptial gifts is determined only on the nutritional value of the gift itself rather than the function within t he female, there is an obvious risk for incorrect conclusions.