Antipredatory behavior as an index of heavy-metal pollution? A test using snails and caddisflies

The loss of behaviors that organisms use to avoid predation may serve as a sensitive indicator of pollution. We tested the hypothesis that a correlati on exists in the field between heavy metal levels and antipredator behavior s. We examined the antipredator behavior of aquatic caddisfly larvae and sn ails at sites in the Coeur d'Alene basin of Northern Idaho which varied in their levels of heavy metals. We tested the antipredator response of Physel la columbiana snails at 10 polluted lakes downstream from the Bunker Hill E nvironmental Protection Agency (EPA) Superfund cleanup-site. We then compar ed their behavior to snails at 14 reference lakes. We placed the snails in a plastic testing apparatus, exposed them to an extract of crushed snail, a nd then monitored their movements to a normally preferred shaded area. We a lso tested the behavior of caddisfly larvae from 36 sites from a total of 6 streams/rivers adjacent to the Superfund site. Sites were located upstream and downstream of abandoned mines. We located active larvae of four genera , simulated predation by grasping the animals between thumb and forefinger (the larvae respond to being grasped by withdrawing into their case), lifte d them from the water for 3 s, and then placed them in an adjacent, slower section of the stream. We then recorded how long it took each larvae to par tially emerge from its case and attempt to move away. Unlike reference site snails, snails from heavy metal-polluted environments failed to exhibit an tipredator behaviors in response to crushed conspecifics. These results are consistent with previous laboratory studies. We found no effect of heavy m etals on the antipredatory behavior of caddisfly larvae.