NUPTIAL GIFTS, RESOURCE BUDGETS, AND REPRODUCTIVE OUTPUT IN A POLYANDROUS BUTTERFLY

Abstract

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 ∼70 eggs. Females use the male-transferred nutrients to increase their pool of nutrients used for egg production and show a positive relationship 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 earlier studies, female thorax mass decreased with age, indicating that old females of P. napi are able to use more of the resources from their thorax than young females. Since male-transferred material also increases female longevity, multiply mated females also use more of their resources from the thorax. Consequently, multiply mated females have a relatively higher reproductive investment than singly mated females, i.e., they transform a larger part of their body reserves to egg production. These results are important for studies that involve male-transferred nutrients in female life history patterns as well as for investigations of links between nuptial gifts and sexual selection theory. When the value of nuptial gifts is determined only on the nutritional value of the gift itself rather than the function within the female, there is an obvious risk for incorrect conclusions.