Flash signal evolution, mate choice, and predation in fireflies.

Many key advances in our understanding of firefly biology and signaling have been made over the past two decades. Here we review this recent research, which includes new phylogenetic results that shed light on the evolution of courtship signal diversity within the family Lampyridae, new insights into firefly flash control, and the discovery of firefly nuptial gifts. We present a comprehensive overview of sexual selection in lampyrids, including evidence from Photinus fireflies that females choose their mates on the basis of male flash signals, and discuss the importance of examining both precopulatory and postcopulatory sexual selection in this group. Finally, we review recent findings on firefly chemical defenses, and discuss their implications for flash signal evolution in response to generalist predators as well as specialist predatory fireflies. This review provides new insight into how firefly flash signals have been shaped by the dual evolutionary processes of sexual selection (mate choice) and natural selection (predation), and proposes several exciting directions for future research.

Nuptial gifts and sexual selection in photinus fireflies.

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.

Flash signals, nuptial gifts and female preference in photinus fireflies.

The evolution of male courtship signals such as the bioluminescent flashes of fireflies may be shaped, at least in part, by female preference for particular characteristics of the male signal. These female preferences for male courtship signals may arise as a result of the benefits of choosing males with particular traits. One possible benefit of mate choice occurs if females can use male courtship signals as an honest indicator of male nutritional contributions at mating, nuptial gifts. This paper reviews female preference for male flash characteristics in Photinus fireflies (Coleoptera: Lampyridae), and the potential for females to use male flash characteristics to predict nuptial gift quality. In Photinus firefly species with single pulse flashes females preferentially respond to flashes of greater intensity and duration. Male Photinus provide a nuptial gift to females at mating in the form of a spermatophore and flash duration serves as a good predictor of spermatophore mass for males collected early in the season. However, Photinus fireflies do not feed as adults, so spermatophore mass decreases with subsequent matings. In response, nutrient-limited females may stop preferentially responding to longer duration flashes, increasing their overall responsiveness later in the mating season as they forage for spermatophores. Therefore, the evolution of male courtship signals in Photinus fireflies is the product not only of female preference for male flash characteristics, but also the costs and benefits of female choice that shape these preferences.