Unveiling the secrets of leatherback turtle (Dermochelys coriacea) mating system: polygamy, polygyny, and sex ratio dynamics of a Brazilian rookery

Studying sea turtle mating behaviour is challenging because of the difficulty of direct observation in their natural habitats. However, advances in molecular biology, particularly microsatellite marker genotyping, have made it possible to investigate these behaviours indirectly. These markers are highly variable and ideal for paternity studies, because the chances of two individuals sharing the same alleles are low. This technique has been widely used to study multiple paternity in sea turtles. In this study, we focus on the endangered leatherback turtle (Dermochelys coriacea), examining multiple paternity and the sex ratio of the reproductive population on beaches near the Doce River, Espírito Santo, Brazil. This is the first investigation of multiple paternity in a Brazilian leatherback population and the first case of polygyny documented in this species. Using six microsatellite markers, we analysed 15 clutches from two nesting seasons (2019–20 and 2020–21). The results showed that 60% of the clutches exhibited multiple paternity, with polygyny observed in 41% of cases, involving one to six males per clutch. Additionally, the sex ratio was found to be 1.42 males per female. These findings establish a foundation for future comparisons with other leatherback populations, providing insights into reproductive sex ratios along the Brazilian coast. This research contributes to our understanding of male gene flow and highlights the need for focused conservation efforts to protect this Critically Endangered species.