Frogs are not commonly thought of as an intelligent species. However, they do have their own unique methods of combating potential harm. Scientists discovered one such technique recently while studying European common frogs in the United Kingdom. It seems that frogs may try to avoid diseases by reproducing at younger ages.

What is the research?

Ranavirus is a typically fatal disease that leads to severe skin scores and internal bleeding. Researchers from the University of Exeter and the Zoological Society of London compared groups (“populations”) of frogs that had been exposed to ranavirus, with groups that had not.

Richard Bartz

Frogs breed beginning at roughly age four in disease-free populations; however, frogs in the virus-exposed populations reproduce as young as age two. The researchers discovered significantly more young frogs and significantly fewer elderly frogs in populations that have the virus.

Frogs in their ponds

Frogs assemble at breeding spots such as ponds and then scatter, but typically return to the same ponds each year. The researchers estimated that for older frogs, returning to the same infested breeding pond increases the chances of affliction and death. This could explain why there are fewer older frogs in ponds that are afflicted with ranavirus.

Lancaster University

The scarcity of older frogs may make it easier for younger – and thus smaller and less competitive – frogs to mate and reproduce. Another possibility is that due to the high mortality rate of older frogs, natural selection favored frogs that have a genetic disposition enabling them to breed at younger ages.

Why does the research matter?

The research indicates that both uninfected and infected populations have the capacity to thrive in normal conditions. However, virus-exposed populations rely on younger breeders that do not produce as many offspring as do older breeders.

Brian Gratwicke

The research team has warned that this decline in breeding age could indicate that virus-exposed populations are at a higher risk of local extinction due to environmental changes. An unfortunate environmental change such as a late frost – that would further decrease the number of offspring produced – could lead the population to collapse. This is not a good situation, considering amphibians are already the most threatened group of vertebrates on the planet, with infectious diseases being a primary contributor to their declines in population.