Frog Abnormalities are Localized: Extra Limbs Less Common Than Missing Toes

Amphibians are continuing to decline in the wild as they face threats from pollution and climate change. Yet there may be some good news for frogs.  A 10-year study has revealed that the rate of abnormalities, such as shortened or missing legs, was less than 2 percent overall. This indicates that the malformations that were first reported in the mid-1990s are a lot less common than originally feared.

When scientists first started reporting abnormalities in the wild, a lot of questions remained. Where and when did these abnormalities occur? Were they widespread or localized? Were the persistent? In order to find that out, the researchers carried out fieldwork at 152 refuges across the country between 200 and 2009. They collected more than 68,000 frogs and toads for the study in order to create a dataset.

So what did they find? The research showed that abnormality hotspots occurred in specific places, but within these hotspots the rate of malformations can change over time. This showed that specific places were being impacted, but not general areas. In addition, the scientists noted that the most common malformations were missing or shortened toes or legs and skin cysts. Only about 12 cases of frogs with extra legs were found.

"We now know what the baseline is and the 2 percent level is relatively good news, but some regions need a deeper look," said Marcel Holyoak, one of the researchers, in a news release.

Currently, the exact cause of these abnormalities is unknown. Yet scientists believe that it could be anything from pollution to parasites to ultraviolet exposure and naturally occurring heavy metals. In fact, these causes may vary from place to place. More research is currently needed to define exactly what may be causing these mutations in specific locations, especially as amphibian populations continue to decline worldwide. The scientists plan to continue investigating this particular issue into the future.

The findings are published in the journal PLOS One.