Multiple stressors on larval amphibians: The effects of herbicide use, predation, and projected warming

Background/Question/Methods

Anurans consist of frogs and toads and are very important in terms scientific research, as well as serving vital ecosystem functions because they are capable of movement between and within aquatic and terrestrial environments. Anuran tadpoles help to regulate energy flow and cycling of nutrients, especially in aquatic systems, because they serve as both predator and prey. By consuming large amounts of algae, tadpoles help to reduce the rate of natural eutrophication, oxygen depletion in several aquatic ecosystems, while also providing a vital link in food webs. Without the presence of anurans, a trophic cascade could be initiated which would affect many other species and lead to a loss in biodiversity.

Over that past several decades, amphibian population declines have been occurring throughout the world, even in protected areas. Threats to anurans and other amphibians include:  habitat modification and destruction, commercial over-exploitation, introduced species, environmental contaminants, global climate change, and infectious diseases. This study provides an examination of several of the threats to anurans by evaluating the effect of multiple stressors on anurans. Specifically, the effect of predation and projected warming temperatures on the toxicity of a commonly used herbicide (Roundup) on Rana catesbienna is analyzed.

Results/Conclusions

Results indicate that multiple stressors have a more harmful effect on tadpole survival then single stressors alone, however; individual stressors such as chemical and predator stressors also have a negative effect on survival and development. In the presence predator and temperature treatments, the herbicide became more toxic to tadpoles than in the absence of predator and temperature treatments. The LC50 rates (rate to kill 50% of a population) of Roundup were lowest (indicating higher toxicity) when all three stressors were present. In treatments where less than 50% of the population was killed, abnormal morphological developments such as asymmetry occurred. These abnormal developments can lead to complications in survival as the tadpoles continue to develop into mature adults. This indicates that multiple stressors can be extremely detrimental to tadpole populations and can lead to mortality in a large number of individuals within the population, while also effecting morphological development in surviving individuals.

This study indicates that anuran species in areas that are susceptible to high use of herbicides may be at high risk to decline. Regulations on the use of herbicides and other chemicals in the environment must be implemented to ensure that further anuran and amphibian declines do not occur.