High Field Pivotal Temperature of Olive Ridley Sea Turtles (Lepidochelys olivacea)

Abstract

All species of sea turtles exhibit temperature dependent sex determination (TSD), where egg incubation temperature during the middle third of incubation determines the sex of offspring. Many hatchling sex ratio studies are performed in laboratory settings where eggs are incubated under constant temperatures. While these studies have helped to establish important information about how incubation temperature affects embryonic development, incubation duration, hatchling performance, and sex ratios, in situ nests experience stochastic conditions, such as daily temperature fluctuations. To better understand the effects of temperature on a TSD species, we evaluate incubation duration, hatchling size, and hatching success as well as determine pivotal temperature and hatchling sex ratios of olive ridley sea turtles (Lepidochelys olivacea) in field conditions where natural stochastic weather fluctuations take place. Eggs were collected and relocated to a hatchery with five different treatment groups aiming to create a thermal gradient for assessing TSD. After hatchlings emerged, nest temperatures and associated sex ratios were determined for each nest. Our study found that the field pivotal temperature for L. olivacea at Ostional, Costa Rica is 31.5°C with a transitional range of temperatures from 30.6°C to 32.5°C. This is the highest pivotal temperature recorded for any species of sea turtle. Establishing a field pivotal temperature is critical for accurate estimations of hatchling sex ratios at nesting beaches along the Eastern Pacific coast. This work adds additional field data on hatchling demography, building on previous field experiments as well as laboratory experiments that are unable to account for field heterogeneity.