Global Warming Raises Extinction Risk from Frog Sex Reversal

Global warming is increasing the risks associated with sex reversal in frogs, potentially threatening amphibian populations and accelerating their decline. A study published in Science Advances on September 3, 2025 highlights how rising temperatures, reproductive disadvantages, and infectious diseases could combine to increase the extinction risk of agile frogs in Hungary.

Sex reversal occurs when an animal develops reproductive characteristics that differ from its genetic sex. Scientists have documented this phenomenon in several animal groups, including fish, reptiles, and amphibians. However, climate change may increase its frequency and create new challenges for species survival.

Global Warming and Frog Sex Reversal: How it affects 

Amphibians already face significant conservation challenges. According to a study published in Nature in 2023, approximately 40% of amphibian species face extinction risk, making amphibians the most threatened vertebrate group.

In agile frogs, sex chromosomes normally determine genetic sex. Two X chromosomes produce genetic females, while an X and a Y chromosome produce genetic males. However, excessive heat during the tadpole stage can override this genetic pattern and cause genetically female tadpoles to develop into fertile males.

Researchers from the HUN-REN Centre for Agricultural Research in Hungary investigated how this temperature-driven sex reversal affects reproduction and survival.

Key Differences: Normal Males vs. Sex-Reversed Male Agile Frogs

Sex-Reversed Male Frogs Have Lower Reproductive Success

The researchers compared 20 sex-reversed males with 20 males whose genetic and physical sexes matched. They examined mating success, egg production, and the development of offspring.

Although sex-reversed males could mate and fertilise eggs, females showed a lower reproductive response to them. Around one-third of females paired with sex-reversed males laid only part of their eggs, potentially reserving the remaining eggs for another mate.

Field observations reinforced these findings. Researchers examined more than 100 egg masses across 16 populations and found that sex-reversed males accounted for approximately 20% of wild males but fathered only 4% of egg clutches.

The offspring also showed greater vulnerability to sex reversal. Researchers found that 61% of offspring from sex-reversed males developed as males despite carrying female-associated XX chromosomes, compared with 17% of offspring from males whose genetic and physical sexes matched.

Heatwaves and Ranavirus Increase the Threat

Climate change can also intensify infectious disease risks. Ranavirus poses a serious threat to amphibians, and some outbreaks have killed more than 90% of tadpoles in a single event.

In laboratory experiments, researchers exposed eggs from both groups of males to artificial heatwaves and ranavirus. Under high-temperature conditions, tadpoles fathered by sex-reversed males carried higher viral loads.

These findings suggest that reduced reproductive success, increased sex reversal among offspring, and greater disease susceptibility could collectively weaken frog populations.

How Temperature-Induced Sex Reversal in Frogs Increase Extinction Risk

Researchers used computer models to assess the combined effects of sex reversal and disease on wild agile frog populations. The models indicated that small populations faced greater risks because losing even a few breeding females could significantly reduce reproduction.

Some populations could disappear within 60–70 years under continued warming and increasing male-biased sex ratios. When researchers included ranavirus-related mortality among offspring of sex-reversed males, population decline began approximately 10 years earlier, and extinction occurred about 9.5 years sooner.

The findings highlight the need to incorporate temperature-driven sex reversal into amphibian conservation strategies. Scientists must monitor genetic and physical sex differences, assess disease susceptibility, and protect breeding habitats to improve the long-term survival prospects of threatened amphibians.