Frogs from groups exposed to deadly virus are being reared in their younger years, new research suggests.
Scientists studying European Common Frogs in the UK compared groups ("populations") exposed to ranavir and those without disease.
While the youngest frogs for breeding in disease-free populations older than four years, frogs in groups that are exposed to viruses grow up as young.
The reasons for this are not yet clear, but the team – under the guidance of researchers at the University of Ekether and the Zoological Societies of London – warns that this age reduction is caused by populations exposed to diseases at a higher risk of local extinction caused by environmental changes.
Frogs are harvested in places such as fishponds, and then they grow, but most return to the same lake from year to year.
"Our research shows that the age of frogs returning to growth varies between the population that is known to have a ranavirus and those who do not work," said Dr. Levis Campbell, who led the research during his doctoral dissertation at the Penrin Campus University in Eketer in Cornwall.
"We found significantly less old frogs and significantly more young frogs in populations that have a ranavirus.
"It is possible that the old frog returns to the same infected reproductive nucleus several times, it is more likely that it will become sick and die.
"The absence of older frogs can then create an opportunity for younger and hence less and less competitive frogs that are successfully developing.
"With high mortality among older frogs, it is also possible that natural selection pressure has favored those who are genetically postponed to work younger."
Ranavirus, first recorded in the United Kingdom during the 1980s, can cause severe skin injuries and internal bleeding. It's usually fatal.
In a new study, which included data collected by citizen scientists, frog cultivation in disease-free populations was usually six to eight years old, while in populations where ranavirus was present, they were generally three to six years old.
Commenting on the differences between two species of frog population, Dr Campbell, now at the University of Visconsin-Madison, said: "Our models suggest that both infected and non-infectious populations can continue to suffer under normal conditions.
"But it seems that populations exposed to diseases are largely dependent on younger breeders who do not produce as many descendants as older, larger frogs.
"For these populations, changes in the environment, such as late frost – which would kill foxes and further reduce the number of descendants produced – could lead to collapse of this population (known as local extinction)."
He added: "We live in times of increasing ecological changes, so understanding how wildlife diseases change the host's ability to deal with such uncertainty."
Dr. Xavier Harrison, from the Zoological Society in London, said: "We often think about the negative consequences of wildlife as the death of infected people in the short term.
"But this study shows that, even when the population seems to have survived the disease and are otherwise healthy, there are still long-lasting effects of this disease, months or years later.
"If we really want to understand the full impact of animal disease in nature, we must monitor populations caused by disease in much longer periods of time."
It is believed that Ranavirus spreads in the United Kingdom, and human activity, such as the movement of animals and land, is considered to be the main cause of this.
Amphibians are the most endangered group of vertebrates globally, and new infectious diseases play a major role in their continuous decline in the population.
Work, published in the journal PeerJ, is called: "The new viral pathogen shortens the age structure of the population in a European amphibian and can reduce the sustainability of the population."