Climate change drives frog sex reversal, threatening extinction

UPDATE - follow-up to Global warming is turning frogs' sex reversal into an extinction risk: Rising global temperatures are causing frequent sex reversal in agile frogs in Hungary, creating a significant threat of extinction for amphibian populations.

Study Findings

Researchers found that genetically female tadpoles turn into fertile males when exposed to excessive heat. Published on September 3 in Science Advances, the study reveals that sex-reversed wild males sire fewer offspring, and these young are more vulnerable to heat and infectious diseases. While sex-reversed males made up 20% of wild populations, only 4% of egg clutches belonged to them.

Offspring Risks

Lab-reared tadpoles from sex-reversed males showed a 61% rate of sex reversal compared to just 17% for normal males. When exposed to an artificial heat wave and the pathogen ranavirus, these offspring carried higher viral loads. Computer models show that small populations could disappear within 60 to 70 years due to these combined pressures, with ranavirus causing population decline to begin 10 years earlier and extinction to arrive 9.5 years sooner.

Context

Amphibians are currently the most threatened vertebrates on earth, with about 40% of species facing extinction risks. Climate-driven changes in wild animal populations can destabilize natural reproduction cycles and ecosystems over time. Earlier report (2026-10-12 13:15): UPDATE - follow-up to Global warming is turning frogs' sex reversal into an extinction risk: Rising temperatures are causing heat-driven sex reversal in agile frogs in Hungary, turning genetically female tadpoles into fertile males and threatening long-term survival.

What Happened

Published in Science Advances on September 3, a recent study examined agile frogs where excessive heat during the tadpole stage overrides chromosomes to turn genetic females into males. Researchers found that while sex-reversed males made up roughly 20 percent of wild populations in Hungary, they accounted for only 4 percent of egg clutches in breeding ponds. Veronika Bokony, lead author from the HUN-REN Centre for Agricultural Research, noted that when frogs mate freely, sex-concordant males are more successful.

Offspring Vulnerability

Offspring of sex-reversed males also face severe disadvantages. About 61 percent of their offspring underwent sex reversal themselves, compared to just 17 percent of offspring from normal males. When exposed to heat waves and the pathogen ranavirus, which can wipe out over 90 percent of tadpoles in a single event, offspring of sex-reversed males carried higher viral loads.

Population Impact

Computer models show that combined pressures of lower paternity, higher rates of sex reversal, and disease susceptibility cause populations to decline years earlier and speed up extinction risks, particularly for small populations. Without ranavirus, populations declined about eight years earlier, while adding virus mortality brought population decline about ten years earlier and extinction about 9.5 years sooner.

Context

About 40 percent of amphibian species face extinction risks, making them the most threatened vertebrates on earth. Heat-induced sex reversal creates a male-skewed population where individuals struggle to find mates, reducing genetic diversity and hastening population collapse. Earlier report (2026-10-12 12:47): UPDATE - follow-up to Global warming is turning frogs' sex reversal into an extinction risk: Rising global temperatures are causing frequent sex reversal in agile frogs in Hungary, creating a chain reaction that raises the risk of population extinction. Scientists published these findings in Science Advances on September 3, revealing that forty percent of amphibian species already face extinction risks.

The Study

In agile frogs, two X chromosomes make a genetic female, but excessive heat during the tadpole stage turns some genetic females into fertile males. Researchers from the HUN-REN Centre for Agricultural Research tested twenty sex-reversed males against twenty normal males in breeding ponds. While normal males succeeded, about one-third of females paired with sex-reversed males laid only part of their eggs in a split clutch strategy. Wild surveys showed that although sex-reversed frogs made up twenty percent of wild populations, they accounted for only four percent of egg clutches.

Offspring Vulnerability

Offspring of sex-reversed males faced severe survival challenges. Sixty-one percent of their offspring underwent sex reversal, compared to just seventeen percent for normal males. Furthermore, when exposed to heat waves and the pathogen ranavirus, which can wipe out over ninety percent of tadpoles in a single event, the offspring of sex-reversed males carried higher viral loads.

Context

Computer models show that small populations are especially vulnerable as heat-driven sex reversal produces more males and fewer breeding females. When factoring in ranavirus mortality, population decline starts roughly ten years earlier and extinction arrives about nine point five years sooner.