Effect of Cr(VI) on early life stages of three species of hylid frogs (Amphibia, Anura) from South America

Abstract

Hylidae are one of the most diverse and widely distributed frog families in the world. The species selected in the present study is representative for the subtropical wetland area of South America. Considering the global decline of amphibian populations, the present contribution is aimed towards the sensitivity of three frog species to a common pollutant, chromium [Cr(VI)]. Toxicity tests were done exposing organisms at two different stages of development (from 24 h embryos to 120 h larvae and from 144 to 240 h tadpoles) using Hyla pulchella, H. nana, and Scinax squalirostris, and measuring mortality and morbidity as end points. Organisms used for testing were obtained from mating pairs collected at a local pond. Assays were done under laboratory standardized conditions with three replications and at least five organisms per replication, using eight dilutions of the toxicant and negative controls. Results of mortality were expressed as 96 h 50% lethal concentration (LC50). Slope of dose–response plots for the three species were obtained by regression analysis. Comparisons were done by simple linear regression equations. Results from regression analysis show that sensitivity of the three species differs significantly (p<0.01). Although the presence of malformations was observed, organisms at earlier stages present a lower sensitivity to chromium. Regarding lethal effects, S. squalirostris is more sensitive (LC50=4.72 mg/L) than the other species (H. nana LC50=10.99 mg/L and H. pulchella LC50=19.67 mg/L) in tests with organisms of the second stage. The present communication contributes to knowledge on the biological effects of Cr(VI) on poorly studied neotropical frog species.