Back in 2013, we announced the results of an unprecedented 10-year-study, published in PLOS ONE, on amphibian abnormalities on national wildlife refuges. We found that on average, less than 2 percent of frogs and toads sampled on 152 national wildlife refuges had physical abnormalities involving the skeleton and eyes—a much lower rate than experts first feared based on earlier reports. This indicated that the severe malformations such as missing or extra limbs repeatedly reported in the media during the mid-1990s were actually quite rare on national wildlife refuges. However, there were a few hot-spot clusters that had higher rates of abnormalities. One of these hot spots was at Kenai National Wildlife Refuge in Alaska.
As part of the follow-up research on this hot spot, we worked with researchers from Alaska Pacific University and the University of California at Davis to understand how and why there were higher rates of abnormalities. We found that wood frog tadpoles were attacked by dragonfly larvae 30 minutes sooner and three times more often in warm, slightly polluted water treatments, than in cooler, pollution-free treatments. The experiments simulated the effects of degraded water quality due to road runoff and climate change.
The researchers studied the interactions of the tadpoles and dragonfly larvae under various water temperature and copper exposure treatments to watch how the animals’ behavior affected their interactions. The tadpoles in the experiment spent more time at the surface of the water making it easier for dragonfly larvae to see and attack them. The dragonfly larvae exerted the least amount of energy to capture more tadpoles in the warm, polluted water treatment. The increased predation observed in this study supports previous research and could also help explain the prevalence of malformed frogs in some refuge hotspots.