An Invasion of CheatsThe Evolution of Worthless Nuptial Gifts

Abstract

Nuptial gifts are food items or inedible tokens that are transferred to females during courtship or copulation [1Vahed K. The function of nuptial feeding in insects A review of empirical studies.Biol. Rev. 1998; 73: 43-78Crossref Scopus (464) Google Scholar, 2Pizzari T. Food, vigilance, and sperm The role of male direct benefits in the evolution of female preference in a polygamous bird.Behav. Ecol. 2003; 14: 593-601Crossref Scopus (51) Google Scholar, 3Thornhill R. Alcock J. The Evolution of Insect Mating Systems. Harvard University Press, Cambridge, MA1983Google Scholar]. Tokens are of no direct value to females, and it is unknown why females require such worthless gifts as a precondition of mating. One hypothesis is that token giving arose in species that gave nutritious gifts and males exploited female preferences for nutritional gifts by substituting more easily obtainable but worthless items [4Sakaluk S.K. Sensory exploitation as an evolutionary origin to nuptial food gifts in insects.Proc. R. Soc. Lond. B. Biol. Sci. 2000; 267: 339-343Crossref Scopus (97) Google Scholar]. An invasion of such behavior would require that females accept the substitute gift and copulate for a period of time similar to that with genuine gifts. We show that both these prerequisites are met in the dance fly Rhamphomyia sulcata, in which females normally accept a nutritious gift. We removed the gift from copulating pairs and replaced it with either a large or small prey item or inedible token. We found that although pairs copulated longest with a large genuine gift, the tokens resulted in copula durations equivalent to those with a small genuine gift. We also observed that males that returned to the lek with tokens re-paired successfully. These findings suggest that female behavior in genuine gift-giving species is susceptible to the invasion of male cheating on reproductive investment.