The role of shell strength in selective foraging by crayfish for gastropod prey

1. Four gastropods common in Wisconsin lakes, Amnicola limosa, Gyraulus parvus, Physella gyrina and Helisoma anceps, were exposed to predation by three crayfish congeners, Orconectes rusticus, O. propinquus and O. virilis in the laboratory to determine prey preference. 2. There were no differences in prey choice among the crayfish congeners, but there were clear differences in electivity for the different snail prey. 3. Crayfish had higher electivities for the thin-shelled, plano-spiral pulmonate Gyraulus parvus, despite its lower abundance in samples, than the thicker-shelled prosobranch Amnicola limosa. Electivity for another plano-spiral pulmonate, Helisoma anceps, was low, evidently because of its relatively thick shell and larger size. Amnicola limosa and the thin-shelled pulmonate Physella gyrina (present at roughly the same relative abundance as Gyraulus parvus) were neither selected nor avoided. 4. Crayfish electivity appears to be a function of the resistance of shells to chipping by crayfish mandibles. Although different species are preferred, this is similar to the previously described selection of thin-shelled species by sunfish.