Growth Plasticity with Changing Diet in the Land Snail Patera Appressa (polygyridae)

Diets of most snail species are unstudied, but the diets of non-native snails are of special interest because these species may be pests or compete with native species. We tested whether the apparent leaf-litter diet of a colony of the non-native land snail Patera appressa from a plant nursery was adequate to support growth, and whether growth rate could be altered by changing diet. Growth was tested in two laboratory experiments using combinations of leaf litter and live plant matter (romaine lettuce). In the first experiment, snails were given a diet of litter, lettuce or both. In the second experiment, the snails from the first experiment were all given both litter and lettuce, and additional colony snails were given only litter (i.e. loss of lettuce). Snails showed rapid growth with live plant material and stunted growth on a diet of only leaf litter, indicating that leaf litter alone is not a good diet and that the snails are likely consuming live plants at the nursery. Changing the diet revealed growth plasticity. The addition of live plant material reversed the previously stunted growth on a litter-only diet, and the stunted snails caught up in size with non-stunted snails. Under conditions of changing food resources, growth plasticity enables large size at maturity, which likely has fitness consequences.