Feeding ecology and maternal effects impact reproductive success in loggerhead sea turtles (Caretta caretta)

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Leila Fouda, Stuart Robert Brian Negus, Emma C. Lockley, Albert Taxonera, Gail Schofield and Christophe Eizaguirre, School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom, Albert Taxonera and Kristen Fairweather, Associação Projeto Biodiversidade, Santa Maria, Ilha do Sal, Cabo Verde

Background/Question/Methods
An efficient foraging strategy is one of the most essential components for the survival and fitness of an organism. To maximize their foraging success, some species have evolved long-distance migrations between their breeding and foraging sites. One of these species is the loggerhead sea turtle (Caretta caretta). Loggerhead sea turtles are capital breeders and must reach a specific energetic resource threshold before embarking on a breeding migration to their nesting grounds, which can be thousands of kilometres away from where they forage. Successful foraging is critical to successful reproduction, as energetic resources derived from foraging are used for key life history traits, from migrating to breeding to clutch formation and nesting. The feeding ecology of cryptic species such as sea turtles can be determined using stable isotope analysis. Here, we used carbon and nitrogen stable isotopes from skin and blood samples for over 200 nesting turtles. These stable isotope values alongside measurements of fat reserves and parasite infection were used to determine the impact of the foraging environment on both reproductive outputs of adult females in terms of clutch size and the fitness of more than 1700 hatchlings in 88 nests.

Results/Conclusions
We found a significant positive correlation between δ15N and clutch size whereby turtles that forage at higher trophic positions (with a larger value of δ15N) produced larger clutches overall. Furthermore, turtles with enriched values of δ13C, likely using a neritic foraging niche, had more fat reserves when uninfected with a sanguivorous leech parasite (F2,207=5.01 p=0.03). Parasite infection carries extra energetic costs, which may not be compensated by feeding, revealing a trade-off between energy reserves for migration and the mounting of an immune response. Additionally, female turtles with enriched δ13C values produced hatchlings that were heavier and performed better at crawling and self-righting trials. These trans-generational maternal effects were altered by the infection status of the nesting females and are likely due to extra resource investment in offspring as a compensatory effect of reduced fitness due to parasitisation. Our study shows successful foraging seasons and the development of significant fat reserves in loggerhead sea turtles are crucial for reproductive success, offspring fitness, and population health.