CAREER: The evolution of female alternative reproductive tactics in a cooperative bird

Princeton University, Princeton NJ

Investigators

Abstract

Individual variation in behavior is widespread in the animal kingdom and it is still unclear how this variation in behavior impacts reproduction and survival in animals. The greater ani is a tropical bird that nests in groups: several females lay their eggs in a shared nest and help to raise the mixed clutch of nestlings. However, some females act as reproductive parasites, laying their eggs into a group's nest but providing no parental care. A female ani can therefore use two alternative tactics for reproduction: she can nest in a cooperative group and help to raise her own young, or she can act as a parasite and let another group do all of the work. But why do some females nest cooperatively, whereas others, in the same population, act as parasites? One goal of this project is to understand whether this behavior difference is due to underlying genetic differences, or whether it results from differences in the females' histories (for example, their body condition or the nutrition that they received during development). A related goal is to understand how a female's reproductive behaviors affect her male mate. Are males more successful if they pair with a parasitic female, or a cooperative female? Conversely, does a male's behavior affect whether his mate acts as a parasite or a cooperator? This research can provide significant insight into why reproductive behavioral variation occurs and how males and females coordinate behavior for maximal reproductive success. Field work for this project will take place in Panama, creating opportunities for formative research experiences for low-income high school and college students in the U.S. Finally, it will enable participation in a New Jersey state prison teaching program that serves one of the most neglected and under-served populations in the country. Individual variation in behavioral strategies poses an enduring evolutionary puzzle. When should selection favor divergent solutions to the same problem, instead of a single optimum? Disruptive selection, in which intermediate behavioral phenotypes have lower fitness than extreme alternatives, is thought to play a crucial role in the evolution of alternative reproductive tactics (ARTs) in male animals. However, the evolutionary dynamics and proximate mechanisms influencing female ARTs remain poorly understood, although such strategies are widespread. The greater ani (Crotophaga major), a tropical bird that nests in social groups, provides a unique opportunity to answer fundamental questions about the evolution of female ARTs. Females typically lay their eggs in communal nests and share reproduction and parental care; however, a small minority of females consistently act as reproductive parasites, laying their eggs into the nest of a host group but providing no parental care. The co-existence of widespread parasitism and non-kin cooperation offers an ideal system in which to test long-standing hypotheses about the evolutionary origins and maintenance of female ARTs. The goals of this project are to 1) evaluate whether disruptive selection on reproductive investment favors discrete parasitic and communal tactics; 2) investigate the environmental and genetic mechanisms determining the expression of these strategies; and 3) understand evolutionary feedbacks between alternative female strategies and male fitness. Data on individual reproductive behaviors will be collected from a long-term field site in Panama, enabling direct estimates of heritability, reproductive output, and reproductive investment from a color-marked population. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.