Heavy Metals Alter the Survival, Growth, Metamorphosis, and Antipredatory Behavior of Columbia Spotted Frog (Rana luteiventris) Tadpoles

Abstract.

Amphibian populations appear to be declining around the world. Although there is no single cause, one factor may be pollution from heavy metals. As a result of mining in the Silver Valley of Idaho, heavy metals have been released into habitats containing many species of sensitive organisms, including spotted frogs (Rana luteiventris). While the gross extent of pollution has been well documented, the more subtle behavioral effects of heavy metals such as lead, zinc, and cadmium are less well studied. We tested the effects of heavy metals on the short-term survival (LC₅₀) of spotted frog tadpoles. Compared to single metals, metals presented together were toxic at lower doses. We also raised the tadpoles in outdoor mini-ecosystems containing either a single heavy metal or soil from an EPA Superfund site in the Silver Valley known to be composed of numerous heavy metals. Exposure to Silver Valley soil resulted in delayed metamorphosis. We tested the ability of metal-exposed tadpoles to detect and respond to chemical cues emanating from predacious rainbow trout. We found that high levels of Silver Valley soil, medium levels of zinc, and medium and high levels of lead resulted in a decreased fright response. Low levels of cadmium, zinc, and lead did not cause a significant effect, but low levels of soil did result in a decreased fright response. Heavy metals may alter interactions between tadpoles and their predators.