Study site and sample collection
Sampling was conducted on Tetiaroa atoll (16°59’ S, 149°34’ E), French Polynesia, during eleven nesting seasons from 2010/11 to 2020/21. Sample collection was authorized and coordinated by the Direction of the Environment of French Polynesia. Tetiaroa atoll has a total surface of 6 sq. km, about 585 hectares of sand, and is divided into 12 islets (Figure 1). Between 2010/11 and 2017/18, 53 to 1316 nesting events per season (July - April) were recorded by the local NGO Te mana o te moana (Touron et al., 2018). Biopsies of approximately 0.5cm3 of skin and muscle tissues were collected from the posterior fin of all the observed females and on all dead hatchlings and embryos found. For a total of 6 nests, more than 10 hatchlings were sampled. The laying date was either recorded when laying was directly observed, or estimated when the nest was discovered. In this case, a confidence interval of ± 3 days was applied to all of the estimations. Since 2010/11, monitoring has gradually increased and by 2016/17, almost all nests were sampled each season. However, nesting females were not always observed. (Touron et al., 2018). Nest parameters such as clutch size, number of hatchlings (estimated from empty eggshells), and number of dead embryos were recorded for each nest. Samples were stored in 90% ethanol and kept at 4°C or -20°C until processing.