Oxidative stress is a potential cost of synchronous nesting in olive ridley sea turtles

Olive ridley sea turtles, Lepidochelys olivacea, exhibit a polymorphic reproductive behaviour nesting in solitary or in mass aggregations termed "arribadas", where thousands of turtles nest at once. Arribadas may provide fitness benefits including mate finding during nearshore aggregations and predator satiation at the time of hatching, but the potential costs of arribada nesting remain understudied. To explore the potential trade-offs of the fitness benefits associated with arribada nesting, we collected blood from olive ridley turtles nesting in arribada and solitary. We measured reproductive and metabolic hormones (progesterone, estradiol, testosterone, thyroxine, and triiodothyronine), triglycerides (TG), non-esterified fatty acids (NEFA) and markers of oxidative damage (4-hydroxynonenal, malondialdehyde, protein carbonyls, and nitrotyrosine). Arribada nesters were bigger and had higher levels of progesterone than solitary nesters. Similarly, thyroid hormones were higher in individuals nesting in arribada than in solitary nesters, while TG and NEFA were positively correlated in arribada but not in solitary nesters. Nesting in arribada was associated with increased lipid peroxidation and protein carbonyls compared to solitary nesting. These results suggest that nesting in arribada is potentially more energetically expensive than nesting solitarily, and that oxidative stress may be a trade-off of the fitness benefits associated with arribada nesting.