Study first to show if nesting heat affects sea turtle hatchling ‘IQ’

(Press-News.org) As sand temperatures continue to rise, concerns about the future of sea turtles are growing. Hotter nests not only skew sex ratios – producing more females – but also reduce hatchling survival, slow growth, and increase the likelihood of physical deformities. Yet one important and often overlooked question remains: does this heat also affect cognitive ability – how well hatchlings can learn, adapt and respond to the rapidly changing world they face from the moment they emerge?

A new study by researchers at Florida Atlantic University’s Charles E. Schmidt College of Science offers a surprising glimmer of hope. They are the first to test whether incubation temperature affects cognitive ability in loggerhead (Caretta caretta) hatchlings – how well they can learn, adapt and problem-solve. While animal cognition has been widely studied in birds and mammals, much is yet to be discovered in reptiles.

Using a Y-maze and a visual discrimination task, the researchers trained hatchlings incubated at two female-producing temperatures (88 F and a hotter 91 F) and then tested their ability to “reverse train” when the task rules changed. Eggs were collected during the summers of 2019 and 2020 from nesting beaches in Palm Beach County.

In the initial acquisition phase of training, approximately four weeks after the turtles hatched, they were trained to associate a food reward with a specific monochromatic pattern such as stripes or a bullseye, which were positioned at the ends of the maze. In the reversal phase, the reward pattern was switched, requiring the turtles to abandon the original association and learn that they would need to go to a different target for the reward. This reversal task measured behavioral flexibility – the ability to adapt to new information, which may be essential for survival in dynamic environments like the ocean.

Unexpectedly, the study results published in the journal Endangered Species Research found no significant differences in learning ability between the temperature groups. In both years, hatchlings from both temperature treatments were able to successfully complete the acquisition and reversal tasks. In 2020, they even performed significantly better during the reversal phase, learning faster than they had during initial training.

“Not only were the post-hatchlings capable of suppressing previously learned behaviors to form new, more advantageous associations, they were able to do so with remarkable speed – often requiring fewer trials than the initial learning phase,” said Sarah L. Milton, Ph.D., senior author and chair and professor in the FAU Department of Biological Sciences. “This surprising level of behavioral flexibility suggests that these young turtles may be better equipped to navigate and adapt to rapidly changing environmental challenges than we previously understood. Such adaptability could prove crucial for their survival in an increasingly unpredictable world.”

However, findings also revealed that higher incubation temperatures negatively affected several key physical traits. Hatchlings from the 91 F nests had shorter incubation durations, lower hatching success, slower post-hatch growth, and more frequent scute anomalies – defects in the scales of their shell. They were also smaller – an outcome that could compromise swimming performance and predator evasion.

“The concern remains very real,” said Ivana J. Lezcano, corresponding author and a doctoral candidate in FAU’s Department of Biological Sciences. “Elevated incubation temperatures are known to produce smaller, less physically resilient hatchlings and cause a significant decline in overall hatching success. Together, this can pose serious risks to population survival. However, our finding that cognitive ability and learning may remain largely unaffected, at least in the short-term, by these higher temperatures offers a hopeful perspective. It suggests that, despite other developmental and physical challenges, these turtles may retain the mental flexibility needed to adapt to their changing environments. This resilience gives us one of the first glimpses of how incubation temperature may affect behavioral traits, though ongoing research is essential to fully understand the long-term implications.”

The researchers stress that while these results are encouraging, they come with caveats. The study only examined temperatures up to 91 F, and nesting beaches in South Florida have already recorded sand temperatures exceeding 93 F to almost 96 F – levels known to severely affect hatching success and hatchling performance. More extreme temperatures could still pose risks to brain development and cognition that weren’t evident at the sublethal range tested here.

Furthermore, while a nest in the field is typically considered “successful” if the majority of the hatchlings emerge from it, the study suggests that survival models may need to go beyond emergence rates and factor in hatchling quality – physical and behavioral alike.

“The hatchlings in our study were able to swiftly adjust to new information despite developmental stressors,” said Milton. “This behavioral adaptability is not just a survival mechanism – it’s a critical evolutionary advantage that may enable them to cope with the complex challenges posed by their shifting habitats. Conservation efforts must prioritize not only the preservation of hatchling populations but also the environmental conditions that support their ongoing cognitive development and resilience.”

As sea turtle embryos are so strongly influenced by the thermal conditions of their nest, understanding how temperature affects not just who survives but how well they are equipped for survival is critical.

This research was supported by the FAU School of Environmental, Coastal, and Ocean Sustainability within the Charles E. Schmidt College of Science.

- FAU -

About Florida Atlantic University:

Florida Atlantic University serves more than 32,000 undergraduate and graduate students across six campuses along Florida’s Southeast coast. Recognized as one of only 21 institutions nationwide with dual designations from the Carnegie Classification - “R1: Very High Research Spending and Doctorate Production” and “Opportunity College and University” - FAU stands at the intersection of academic excellence and social mobility. Ranked among the Top 100 Public Universities by U.S. News & World Report, FAU is also nationally recognized as a Top 25 Best-In-Class College and cited by Washington Monthly as “one of the country’s most effective engines of upward mobility.” As a university of first choice for students across Florida and the nation, FAU welcomed its most academically competitive incoming class in university history in Fall 2025. To learn more, visit www.fau.edu.

 

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