Low rate of multiple paternity and an even breeding sex ratio in hawksbill turtles of the Eastern Caribbean

Understanding the breeding biology of endangered species, including breeding sex ratios (BSRs) and relative contributions of breeders to the next generation, is important for assessing population resiliency. Determining BSRs is especially relevant for species with temperature-dependent sex determination, such as marine turtles, to track potential shifts in BSRs driven by climate change. However, complex oceanic life cycles for marine turtles hinder research on individuals and life stages beyond nesting beaches, resulting in a comparative paucity of information regarding breeding males. Here, we estimated the BSR and described mating behavior for Eastern Caribbean (EC) hawksbill turtles Eretmochelys imbricata by reconstructing paternal genotypes with genetic assays of nesting females and their hatchlings at Jumby Bay, Antigua. We genotyped 821 hatchlings from the nests of 23 females with 5 microsatellite markers and generated paternal identities with a maximum-likelihood full-pedigree reconstruction program. Overall, 24 discrete male genotypes were reconstructed from the nests of 23 females, suggesting an even within-season BSR. We found single paternity for the nests of 21 out of 23 females (91.3%) and multiple paternity for the remaining 2 females (8.7%), with primary paternal contributions of 57 and 80%, respectively. One male sired the clutches of 2 different females, providing evidence of polygyny. Finally, fathers identified from the second nests of 6 females matched the fathers identified from first nests, indicating no inter-nest mating occurred. Our results provide baseline data for EC hawksbills to track BSRs over time, and according to ’convenience polyandry’, suggest a low density of breeding individuals in the region.