Chapter 2 - The Evolution of Animal Nuptial Gifts

Abstract

Abstract Animal nuptial gifts display multitudinous forms, and such gifts are especially interesting because they sit at the intersection of sexual selection, foraging ecology, and life-history evolution. However, even though such gifts are likely to play key roles in sexual selection and conflict, remarkably little is known about the selective agents responsible for their origin and maintenance. In this chapter, we propose a classification scheme based on (1) how gifts are produced (endogenous vs. exogenous) and also (2) how they are absorbed by the recipient (oral, genital, or transdermal). This classification provides a conceptual framework that should prove useful for formulating and testing predictions about how different gift types affect fitness of both males and females. Moving beyond earlier work that had coerced potential benefits to gift-giving males into the falsely dichotomous categories of parental investment versus mating effort, we illustrate how nuptial gifts might enhance male fitness across multiple selection episodes that occur before, during, and after mating. Finally, we highlight a few studies that have used comparative phylogenetic methods to see how nuptial gifts and other life-history traits may have changed over evolutionary time. One such study analyzed the evolutionary trajectories of spermatophore gifts within firefly beetles (Coleoptera: Lampyridae), revealing that male gifts have undergone correlated evolution with female flight ability. Thus, this study supports the idea that shifts in female resource allocation may potentially drive male investment in nuptial gifts. Looking forward, phylogenetic analyses across different taxonomic groups will be needed to provide insight into the evolutionary origin and maintenance of nuptial gifts. By including relevant ecological and life-history traits associated with resource allocation, such studies will undoubtedly expand our understanding of nuptial gift evolution.