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Foraging for nutrients? Dietary and reproductive biomarkers in a generalist apex predator reveal differences in nutritional ecology across life stages

Bianca de Sousa Rangel*, Neil Hammerschlag*, James A. Sulikowski, Renata GuimarĂ£es Moreira

*Corresponding author:

ABSTRACT: Knowledge of the nutritional requirements of apex predators is key for determining ecological interactions. However, an understanding of how diet is influenced by reproduction, and the consequences of foraging variation on a predator’s nutritional quality, is limited. Here, we used short-term dietary markers (plasma and whole blood fatty acids) integrated with reproductive hormones (17β-estradiol and testosterone) and ultrasonography as a non-lethal approach to investigate the effect of life stage on nutritional quality and trophic dynamics of female tiger sharks (Galeocerdo cuvier). Despite their generalist feeding behavior, female tiger sharks fed on different food sources and/or modulate their fatty acid metabolism depending on the reproductive context. This suggests some adjustment in their nutritional requirements associated with changes in their reproductive state. Plasma and whole blood fatty acids indicated distinct dietary sources across life stages, with a high dependence on coastal/benthic food resources during juvenile life stages, and on pelagic/oceanic and reef-associated food resource during adult life stages. Higher percentages of highly unsaturated omega-3 fatty acids found in females during their reproductive cycles suggest the dependency on these fatty acids as a source of metabolic energy during reproduction. A high percentage of arachidonic acid (ARA) found in plasma of gravid females suggest the possibility of a selective diet on ARA-rich prey species and/or selective mobilization of ARA from stored energy during gestation. Based on our findings, we propose a conceptual model of expected changes in nutritional and trophic markers across life stages of female tiger sharks.