New publication on climate and sex-ratio!

Santidrián Tomillo, P. 2022 When population-advantageous primary sex ratios are female-biased: changing concepts to facilitate climate change management in sea turtles. Climatic Change 175, 15, doi: https://doi.org/10.1007/s10584-022-03470-4

Abstract: Sea turtles have temperature-dependent sex determination. Because females are produced at high temperatures, increasing global temperature may lead to population feminization. Primary sex ratios (PSR) of sea turtle hatchlings are naturally female-biased, but this translates into a more balanced operational sex ratio because male turtles reproduce more often than females. As a consequence, a balanced PSR and the temperature that produces it (pivotal temperature) are of limited use to guide climate mitigation management because an equal PSR may be demographically suboptimal. 

Photo from wikipedia.org

Here, I define population-advantageous primary sex ratios (PA-PSR) as the PSR that will tend to be in equilibrium in a population and that will result in balanced operational sex ratios; I then estimate PA-PSR for different reproductive frequencies (years elapsed between reproductive seasons) of adult female and male turtles. I also define population equilibrium temperature (PET) as the temperature that would result in the equilibrium PSR of hatchlings (i.e., PA-PSR). These concepts may help assess the influence of rising temperatures on populations, as they can better indicate if PSRs depart from those at equilibrium. I compared PA-PSR and beach PSR for two populations of sea turtles for which male and female remigration intervals were known and found that a mild or no feminization over the PA-PSR may be occurring. Because PSR varies inter-annually, and hatchlings coming from beaches of different thermal conditions could recruit to the same population, it is critical to estimate beach PSR at the right temporal and spatial scales. Climate mitigation strategies based on these concepts could provide better management guidance for conservation practitioners. Similar approaches could be considered for other female-biased species with temperature-dependent sex determination.

New publication on marine Turtles!

Heredero Saura, L., Jáñez-Escalada, L., López Navas, J., Cordero, K. and Santidrian Tomillo, P. 2022 Nest-site selection influences offspring sex ratio in green turtles, a species with temperature-dependent sex determination. Climatic Change 170, 39 (2022). DOI: 10.1007/s10584-022-03325-y

 Abstract: Climate change threatens species with temperature-dependent sex determination as further warming could result in extremely biased sex ratios or offspring of only one sex. Among the possible adaptations of sea turtles to climate change, are behavioral responses toward nesting in cooler areas. We analyzed nesting patterns of East Pacific green turtles (Chelonia mydas) in Costa Rica to determine the occurrence of nest-site selection and how this could influence primary sex ratios (PSR). Green turtles exhibited nest-site repeatability. Nests placed by the same individual were generally closer (mean distance: 237.4 m) than other nests on the beach (mean distance: 411.0 m) and this repeatability was maintained in different nesting seasons. 

Photo from www.fisheries.noaa.gov

Additionally, turtles tended to place late nests closer to each other than their early nests, suggesting an adjusting nesting behavior throughout the nesting season. A great majority of nests were placed in the vegetation (80.9%) and within this zone, turtles preferred nesting under trees (78%) than in grass areas (28%), where temperatures were cooler and PSR were less female biased. Mean nest temperature (°C) during the thermosensitive period and mean PSR were 30.7 ± 1.2 °C and 79 ± 4%, respectively. Most years were female-biased or extremely female-biased but there was approximately one male-biased year in the decade. Although many nests produced 100% females, some male hatchlings were produced every year, even during the extreme 2015–2016 El Niño event. The preference of green turtles for nesting in shaded areas could help to mitigate the negative impacts of climate change unless temperatures in shaded areas rose above the male producing temperatures.

 Press releases in Spanish here and here