Influence of Age and Body Size on Alarm Responses in a Freshwater Snail Pomacea canaliculata

A hypothesis that size selection of prey by predators elicits size-specific responses from prey was examined. Freshwater snails, Pomacea canaliculata, ages 1, 3, 7, 15, 30, or 60 days, were given an extract of 3-day-old snails, and 3-day-old snails were given extracts of snails of the other ages or eggs. Snails 15 days or younger crawled out of the water in response to the 3-day-old snail extract, but older ones did not. The 3-day-old snails responded to the extracts of snails of all examined ages, but not to the extract of eggs. Snails of four size classes, 3-days-old, small (shell lengths 8–12 mm), medium (13–20 mm), and large (>28 mm) were given extracts of snails of each of these four classes. The 3-day-old snails crawled out of the water in response to the extract of 3-day-old snails, but showed a lower or no response to other extracts. Larger snails buried themselves in the soil in response to the extract of snails of similar sizes. These responses are discussed in the context of the evolution of the snail's avoidance behavior in response to the size-dependent prey choice by the predator.