CAREER: Turtle or egg: Characterizing sea turtle reproductive strategies

The goal of this research project is to apply new methods to reliably characterize the extent of capital breeding in three sea turtle species and to test whether reproductive strategy is related to environmental conditions. Reproduction is one of the most basic and important aspects of animal life history. Capital and income breeding represent opposite strategies to fuel reproduction, with capital breeders relying on stored energy, and income breeders relying on food intake during the reproductive period. Sea turtles were long thought to be capital breeders and to fast during reproduction because of the long migrations they undergo from their foraging grounds to nesting areas. However, increasing evidence suggests that some individuals feed during this time. Two major challenges in understanding sea turtle reproductive strategies are that the methods to determine whether sea turtles feed between successive nesting events have not been reliable, and the drivers of variability in breeding strategies are not well understood. Thus, the research will fill an important gap in knowledge about sea turtle energetics and reproduction, with implications for conservation and management of these endangered species. Training and learning opportunities will be provided to a diverse audience, including an undergraduate immersion course in sea turtle biology and conservation, with an emphasis on effective science communication methods. In addition, the methods and theories of isotopic analyses will be incorporated into a graduate-level class, contributing to training and workforce development. The sea turtle clade offers the opportunity to explore variation in reproductive strategy in the context of environmental conditions. The proposed study will (1) characterize variability in capital breeding within and among three sea turtle species and determine how nutrients are allocated to the synthesis of egg components and (2) relate breeding strategy to environmental characteristics and reproductive success. Stable isotope analysis has a long history of identifying trophic and movement patterns in animal ecology, but recent advances allow carbon and nitrogen isotopes to be measured in individual amino acids. This project uses that method to provide a biochemical fingerprint of capital breeding by classifying the source of nutrients (endogenous vs. exogenous) used to fuel metabolism and produce eggs. Identifying the source of nutrient allocations to reproduction can illuminate the evolution of basic life-history trade-offs and characterize the links between organismal physiology and the environment across the annual cycle in these migratory marine consumers. This CAREER award provides a lens through which to elucidate mysteries about reproductive strategies for a group of animals of conservation concern, demonstrates application of novel technologies, and delivers educational components that bridge international experience with science communication. A graduate student and post-doctoral fellow will be involved in the research, and the research team will participate in local outreach activities to a non-scientific audience. 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.