An empty stomach is not a good adviser: avoiding toxic Cyanobacteria can compromise tadpole antipredator defenses

Abstract Eutrophication events resulting from increased primary production are becoming common under changing environmental conditions that include habitat degradation and disturbance of food webs. They cause several detrimental ecological consequences including the intoxication of animals that ingest toxic Cyanobacteria. We tested whether the tadpole of an anthropophilic frog ( Scinax longilineus ) would avoid feeding on a potentially toxic Cyanobacteria using Raphidiopsis raciborskii as a model. We maintained tadpoles in water collected from a natural monospecific growth of R. raciborskii at the original concentration (100%) and concentrations of 0, 25, 50 and 75% of the original sample diluted in rested tap water. We evaluated the amount of R. raciborskii ingested by the tadpoles and conducted behavioral tests by exposing tadpoles to an aversive stimulus and quantifying their escape response. Tadpoles ate the least R. raciborskii the highest the concentration of this Cyanobacteria was in the water. Tadpoles exposed to 50 and 75% of the original concentration of the R. raciborskii sample had a reduction of time spent escaping, what is likely to compromise their ability to escape a real predator attack. Tadpoles at the highest concentration (100%) did not show significant changes in their escape performance, however they practically stopped feeding, what would not be a solution in the long term (i.e., duration of a real bloom). We conclude that tadpoles of S. longilineus can recognize the presence of R. raciborskii and avoid its ingestion, with potential sub-lethal effects represented by a reduced ability to escape predators.