Natal homing in male green turtles (Chelonia mydas) from two neotropical islands

Studying the origins of male green turtles is critical for assessing their poorly understood natal homing behavior, compared to that of females, which have a high degree of fidelity to their nesting beach of their birth. Between 2005 and 2012, we collected 379 tissue samples from male and female green turtles ( Chelonia mydas ) to test the hypothesis that there is no difference in natal homing between the sexes in two tropical Island mating areas of the western Atlantic: Isla de Aves, Venezuela, and Atol das Rocas, Brazil. We sequenced an ~800bp fragment of the mtDNA control region from each individual and characterized their haplotype profiles. Comparisons between males and females from rookeries and their closely associated offshore courtship areas revealed no significant genetic differentiation between males and females at either site, suggesting that males also return to their hatching site to breed. To examine fidelity of males to their natal region in more depth, we combined our results with published data from 2,350 individuals from 31 green turtle rookeries in the Gulf of Mexico, Caribbean Sea, Atlantic Ocean, and the Mediterranean Sea. Considering contributions of 1% or more, a mixed stock analysis of four regional haplotype groups revealed that adult males sampled at Isla de Aves originated from rookeries in the eastern Caribbean, mainly from Isla de Aves itself (95.3%). Also, haplotype frequencies indicated that adult males sampled at Atol das Rocas originated mainly from Atol das Rocas (74.5%), possibly with small (on average 4%) contributions from five other regional rookeries. These combined results also suggest that males from both Isla de Aves and Atol das Rocas return to their natal regions to reproduce, as do females. This study provides the first direct evidence of male natal homing in green turtles in two populations of the western Atlantic and confirms that this phenomenon, previously observed in Australian green turtles, also occurs there. Understanding the factors that contribute to varying degrees of homing to courtship areas is essential for evaluating the demographic independence of populations. It further allows for a more accurate assessment of their vulnerability to regional threats.