Frogs exposed to deadly virus breed younger

Frogs from groups exposed to a deadly virus are breeding at younger ages than those free from the disease, research suggests.

Scientists found the youngest breeding frogs in populations affected by ranavirus were aged two, while those in disease-free areas bred from the age of four.

The team, led by researchers at the University of Exeter and ZSL’s Institute of Zoology, warn this decrease in breeding age means disease-ex- posed populations are at greater risk of local extinction from environmental changes.

Frogs gather at breeding spots such as ponds and then disperse, with most returning to the same ponds year after year.

Dr Lewis Campbell, who conducted the research during his PhD at the University of Exeter, said: “We found significantly fewer old frogs and significantly more young frogs at populations which have ranavirus.

“It’s possible that the more times an older frog returns to the same infected breeding pond, the more likely they are to become diseased and die.

“The absence of older frogs may then create an opportunity for younger – and therefore smaller and less competitive – frogs to successfully breed.

“With high mortality among older frogs, it’s also possible that natural selection pressure has favoured those that are genetically disposed to breed younger.”

Ranavirus, which was first recorded in the UK in the 1980s and is usually fatal, can cause severe skin sores and internal bleeding. In the study, which incorporated data collected by citizen scientists, breeding frogs in disease-free populations were usually aged between six to eight years old.

But those in populations where ranavirus was present were mostly aged three to six years old.

Dr Campbell, now of the University of WisconsinMadison, said: “Disease-exposed populations appear to depend heavily on younger breeders that don’t produce as many offspring.”

PA Frogs gather at breeding spots such as ponds and then disperse