New research suggests sea turtles possess an epigenetic mechanism that helps maintain balanced sex ratios despite rising temperatures from global warming. This adaptation could mitigate fears of population collapse due to excessive female hatchlings. Scientists from Queen Mary University of London led the study on loggerhead turtles.
Biologists have long worried that climate change could doom sea turtle populations by skewing hatchling sex ratios toward females. Warmer nest temperatures, which determine turtle sex rather than chromosomes, might lead to too few males for reproduction. However, a study published on bioRxiv reveals an epigenetic safety net involving DNA methylation that adjusts sex development sensitivity to heat.
Chris Eizaguirre at Queen Mary University of London and colleagues conducted lab experiments with 240 loggerhead turtle eggs from seven nests in Palm Beach County, Florida. Incubated at 27°C for males, 30°C for equal ratios, and 32°C for females, the eggs showed distinct gene activity patterns. Blood samples from 1- to 3-day-old hatchlings, verified later by surgery, indicated 383 genes hypermethylated in females and 394 in males—many linked to sex development. This allowed non-invasive sex identification.
In a field test on Sal Island, Cape Verde, the team split 29 egg clutches: half buried 55 cm deep for cooler conditions, half at 35 cm for warmer. Monitoring 116 hatchlings, they found more males than temperature models predicted, with overestimations of females by 50 to 60 percent.
"We believe we have uncovered the capacity of turtles to adjust to the environment they are in," Eizaguirre said. He emphasized that while feminization persists and climate change accelerates, diverse populations can evolve responses. "When the populations are large enough, when there is sufficient diversity, then it looks like the species [can] evolve in response to the climate they live in."
This aligns with findings by Graeme Hays at Deakin University, Australia, showing higher male hatch rates than expected. Additional behaviors, like earlier nesting and frequent male migrations to breeding grounds, further balance ratios, as males breed more often than females, who skip years.
Such molecular and behavioral adaptations offer hope for these vulnerable reptiles amid ongoing warming.