Effects of copper, zinc and dragonfly kairomone on growth rate and induced morphology of Bufo arabicus tadpoles

It is well documented that many amphibian species can detect chemical signals from predatory invertebrates and subsequently develop alternate phenotypes that are protective against predation. The effects of metallic pollutants on the development of predator-induced morphology have not previously been reported. Tadpoles of the Arabian toad Bufo arabicus were exposed for 20 days to copper (0, 10 or 100 μg/L), zinc (0, 10 or 100 μg/L) and kairomones of larval dragonflies (Crocothemis erythrea 1 dragonfly/12 L) in a fully crossed design. The effects of these treatments of growth and body shape were measured. Measured copper concentrations after 24 h were 4.25 μg/L±1.30 (10 μg/L nominal) and 34.9 μg/L±2.15 (100 μg/L nominal). Measured zinc concentrations were 3.04 μg/L±0.1 (10 μg/L nominal) and 26.3 μg/L±12.3 (100 μg/L nominal). Tadpoles exposed to 34.9 μg/L copper were significantly lighter and had a shorter body length than other groups. There was no direct effect of zinc on growth or tadpole shape. Tadpoles exposed to dragonfly kairomones were heavier, wider and had deeper bodies when viewed laterally and had longer tails but overall length was not affected. At 4.25 μg/L copper differences between the control and predator-exposed phenotypes increased but at 34.9 μg/L the phenotypes converged, indicating that copper may inhibit the induced response.