Online ISSN: 1477-9145

Print ISSN: 0022-0949

© 2026. Published by The Company of Biologists

2026

J Exp Biol (2026) 229 (13): jeb252949.

Sunburn is no joke, especially in the Southern Hemisphere where depleted ozone provides less protection from UVB than in the north. Humans can seek shade and apply chemical sunscreens to exposed skin, but amphibians are particularly vulnerable and tadpoles even more so. ‘This is a time of rapid cell division and significant developmental milestones, making them particularly sensitive to UVB-induced DNA damage’, says Niclas Lunsdgaard, of The University of Queensland (UQ), Australia. The consensus was that the seriousness of sunburn is directly linked to the degree of exposure, so a long weak dose of UVB would yield the same DNA damage as a short intense dose that resulted in the same overall exposure. But Lundsgaard, Craig Franklin and Rebecca Cramp (also from UQ), weren't so sure. ‘A short intense UVB exposure can be three times more lethal for striped marsh frog tadpoles than an equal dose of long weak UVB exposure’, says Lundsgaard. Knowing that UVB damages amphibian DNA in a very specific way, Lundsgaard and his colleagues decided to find out how badly the DNA of developing striped marsh frog (Limnodynastes peronii) tadpoles was affected by short strong versus long weak doses of UVB that added up to the same total exposure.

Collecting recently laid frogspawn from a creek in Brisbane, Lundsgaard returned to the UV-free lab where the tadpoles hatched and developed for 5 weeks. Then, he turned on the UVB, making sure that different tadpoles got the same total exposure of UVB, no matter how strong the dose, by adjusting how long the UV lights were on for. Some tadpoles received one intense (80 μW cm⁻²) dose of UVB – simulating the light levels in a clear pond – for 1 hour, while others received a second strong hour-long dose a day later. Meanwhile, he turned down the sun lamps for other tadpoles, so the UVB was less intense (40 μW cm⁻²), but kept the lamps on for 2 h so the tadpoles received the same overall exposure, with a fourth group of tadpoles receiving a second weak dose of UVB a day later. Then, Lundsgaard checked for evidence of DNA damage. Would the stronger UVB doses be more damaging for the developing tadpoles?

Alarmingly, the strength of UVB that the developing tadpoles experienced had a dramatic impact. The tadpoles that experienced the most intense doses of UVB accumulated damage almost three times faster, resulting in 47% more DNA damage than the tadpoles exposed to mild sunburn. Lundsgaard then checked the tadpoles that were exposed to UVB on consecutive days, and the tadpoles that had experienced the strongest sunburn were in worse shape than the tadpoles that had only received mild UVB doses. The intensely sunburned tadpoles carried over twice as much DNA damage into the second day, and the tadpoles that experienced 2 days of sunburn had 20% more DNA damage than the tadpoles that only experienced sunburn on a single day. Surprisingly, Lundsgaard noticed that the smallest tadpoles seemed to suffer the most DNA damage, experiencing 50% more than their larger siblings, thanks possibly to their larger surface area relative to their mass.

Even though the striped marsh frog tadpoles had experienced the same amount of UVB, the strength of the sunburn made an enormous difference. The tadpoles exposed to the high UVB dose accumulated more dangerous DNA damage than those that had received the same total UVB exposure over longer periods, leaving them at greater risk of mortality. Lundsgaard also warns that fish and corals could be in similar danger from the sun's rays. ‘The larvae of other aquatic animals might struggle with more frequent exposure to short, intense UVB’, he says.