Nuptial gifts and sexual selection in Photinus fireflies

Abstract

The phenomenon of nuptial gift transfer during mating occurs across a remarkably wide range of taxa, and such male donations are likely to influence both pre-copulatory and post-copulatory sexual selection. This paper reviews what is known about nuptial gifts in Photinus fireflies (Coleoptera: Lampyridae), and discusses the adaptive significance of spermatophores in firefly mating systems. During copulation Photinus males transfer a spiral gelatinous spermatophore to the female: sperm are released into the female's spermatheca for storage, while the remainder of the spermatophore disintegrates within a specialized gland. Radiolabelling studies indicate that male-derived protein is used to help provision the female's developing oocytes, and multiply-mated females show increased fecundity. As most Photinus adults do not feed, these studies suggest that females should continue to forage for matings to supplement their diminishing larval reserves, even after they have gained sufficient sperm to fertilize their eggs. Male spermatophore mass declines across sequential matings, and smaller spermatophores are associated with lower paternity success in situations where males compete for fertilizations. Declining spermatophore size across sequential matings may thus lead to diminishing reproductive returns for firefly males. Taken together, these results suggest that seasonal changes in nuptial gift availability may contribute to reversals of traditional courtship roles, with male choice and female-female competition occurring as spermatophore availability declines.