INTRACLUTCH EGG CANNIBALISM BY HATCHLINGS OF THE LAND SNAIL ARIANTA-ARBUSTORUM - NONRANDOM CONSUMPTION OF EGGS

Under natural conditions hatchlings of the land snail Arianta arbustorum cannibalize unhatched sibling eggs as well as eggs from neighbouring batches. Three series of choice experiments were conducted to determine whether cannibalistic hatchlings of A. arbustorum from four different populations discriminate (1) between fertilized and unfertilized eggs within the same batch, (2) between eggs containing well-developed embryos and ones with less advanced embryos, and (3) between small and large fertilized eggs. Newly-hatched snails did not discriminate between fertilized and unfertilized conspecific eggs. Similarly, hatchlings cannibalized in equal proportions eggs with well-developed embryos and eggs with less advanced embryos. However, cannibalistic hatchlings ate preferentially large eggs. The results of an additional choice experiment indicated that this size preference may be due to a higher encounter probabillity and/or a stronger attraction by chemical cues of larger eggs, and thus is not an actual choice made by the cannibalistic hatchling. It is suggested that the higher susceptibility of large eggs to cannibalism may act as selection pressure against increasing egg size.