Effects of temperature on sea turtle sex ratio and individual fitness

• Autor(a) principal: Afonso, Inês Oliveira
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/33254
• topic: Cabo Verde; Climate changes; Conservation; Hormones; Loggerhead turtle; Sex determination

Sea turtles are globally endangered because of poaching, fisheries’ bycatch, pollution, pathogens and coastal development, as well as climate change. It is known that all sea turtles’ sex is determined mainly by the temperature at incubation, with higher proportion of females being produced in higher temperatures. Due to this, it is expected that global warming will influence sex ratios, with a higher proportion of females being produced as temperature increases. However, over the last 120 million years, turtles have survived several changes in climatic conditions of both higher and lower temperatures. How they survived and whether evolutionary processes are implicated remains unknown. Recently, it has been proposed that several other factors may alter sex determination during embryogenesis besides temperature, with evidence that maternal hormone transfer into the eggs could be one of these factors. The presented work aims to help clarify this aspect, utilising loggerhead turtle (Caretta caretta) as a target species. The fieldwork was conducted in Cabo Verde on Sal island, which is one of the main nesting islands of the archipelago. Clutches from nesting females were split into 2 groups and buried at 2 different depths and temperatures, monitored regularly within a protected hatchery exposed to natural weather conditions. After hatching, blood samples were collected from hatchlings for non-lethal sex determination, as well as biometric and fitness traits to better understand the consequences of increasing temperatures. Using the period of incubation and the ratio of oestradiol to testosterone from the blood samples, we determined the neonates’ sex and the sex ratios of all nests. Comparing the measured sex ratios with predicted ones from temperature alone allowed verification of the existence of more males than temperature would predict. In deeper nests, neonates were larger and showed higher fitness than those in shallow conditions. Overall, the presented results reinforce growing evidence that sex of temperature-dependent sex determination species is not only determined by temperature. A better understanding of all factors involved in the process of sex determination, will be crucial for taking conservation measures to preserve species, such as sea turtles.