A cost of mating in female fruitflies

Abstract

COSTS of reproduction occur when an increase in reproductive rate reduces future reproduction by increasing mortality or reducing fertility. Such costs have been demonstrated in plants and animals in laboratory and field studies^1–5. Their importance lies in their possible role in the evolution of life histories and of senescence^6–15. An understanding of their mechanisms will also reveal the nature of the physiological constraints on longevity and fertility. Most accounts assume that these occur as a result of competition for nutrient allocation between growth, storage, somatic maintenance and reproduction^16–21. An increase in reproductive rate would then result in a denial of nutrients to other processes, resulting in a drop in life expectancy or future fertility. Some support for this point of view comes from the finding that lifespan is lengthened in female Drosophila melanogaster that have inactive or absent ovaries^22–23 or that are experimentally induced to produce fewer eggs²⁴. Increased exposure to males, however, also results in a drop in lifespan^24–26. We show here that mating with males greatly reduces lifespan in female fruitflies whose rates of egg-production and egg-fertility do not differ, suggesting both that simple nutrient allocation to reproduction is not its only physiological cost, and that males can cause females to remate at a frequency that results in reduced female lifetime reproductive success.