Fear of the Vegetarian

Brian Langerhans and Thomas deWitt of the department of Wildlife and Fisheries Sciences at Texas A&M University examined the specificity with which freshwater snails use environmental cues to induce defensive phenotypes such as shrinking. In one environment they introduced a species of sunfish that eats snails, In the other a non-molluscivorous, plant-eating, sunfish. Despite the lack of appetite in the latter species snails in both environments developed predator avoidance behaviour, either by developing more rotund shells that are harder to crack, or by becoming smaller, making it more difficult and less calorie-efficient for the sunfish to hunt for them.

The research shows that size-reduction in snails can be induced without exposure to real danger. They just need to believe they are in danger. Perhaps inducing such a response through environmental cues works for people as well? Who, or perhaps what, is our sunfish? Is there a friendly danger signal to help us shrink before the ecosystem collapses?