Wood Frog Tadpoles Adjust Growth to Survive Ranavirus
New study suggests that wood frog tadpoles may survive ranavirus outbreaks by accelerating their growth and development.
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Amphibians face increasing risks from habitat loss, climate change, pollution and emerging diseases. One such disease, ranavirus, has been linked to mass die-offs of frogs and salamanders worldwide. This virus spreads easily among amphibians, fish and reptiles, often leading to high mortality rates.
However, a new study published in Frontiers in Amphibian and Reptile Science suggests that some amphibians may not be entirely defenseless. Researchers found that wood frog (Rana sylvatica) tadpoles can adjust their growth and development in response to ranavirus, potentially improving their chances of survival.
Ranavirus
A group of viruses that infect amphibians, fish and reptiles, causing rapid disease outbreaks that often lead to mass mortality.Tracking wood frog responses to ranavirus
Between 2021 and 2023, researchers monitored wood frog populations in Connecticut, comparing three types of ponds: those with no ranavirus, those with infections but minimal mortality, and those where outbreaks killed all tadpoles.
Over several months, they collected and analyzed 1,583 tadpoles for ranavirus infection, measuring their body size and developmental stage. They found that tadpoles in infected ponds initially grew and developed faster than those in uninfected ponds. In ponds where the infection did not cause mass mortality, tadpoles remained larger and more advanced in development compared to those in uninfected ponds.
Adaptive changes in growth and development
In ponds where ranavirus led to a complete die-off, tadpoles initially showed accelerated growth but later experienced a sharp decline in both size and development as the outbreak progressed. This suggests that while early growth acceleration might help some individuals survive, it is not always sufficient to prevent widespread mortality.
“These responses are likely to give tadpoles a survival advantage. We hypothesize they are the reason why mortality wasn’t always 100%, but only partial in some outbreaks in our study,” said Dr. David Skelly.
The researchers propose that this rapid development could serve two purposes:
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Enhancing immune defenses: By increasing body size early, tadpoles may improve their overall health and immune response.
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Escaping the virus: Faster development could allow tadpoles to metamorphose earlier, leaving the water before infection becomes severe.
Metamorphosis
The process by which amphibians transition from an aquatic larval stage to a terrestrial adult form, involving significant physical changes.Future research directions
The study highlights a potentially important survival strategy in amphibians but leaves key questions unanswered. It remains unclear how tadpoles detect the presence of ranavirus in their environment – whether through chemical signals or other cues – and how effective these responses are in preventing infection.
Further research will be needed to determine whether these developmental adjustments improve overall survival rates in natural settings. Understanding these mechanisms could provide insights into how other species respond to disease threats in changing ecosystems.
Reference: Billet LS, Skelly DK. Sublethal effects of a mass mortality agent: pathogen-mediated plasticity of growth and development in a widespread North American amphibian. Front Amphib Reptile Sci. 2025;3:1529060. doi: 10.3389/famrs.2025.1529060
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