Possible Benefits of Egg Cannibalism in the Land Snail Arianta arbustorum (L.)

Hatchlings of the land snail Arianta arbustorum (L.) were used to test whether the ingestion of conspecific eggs confers nutritional advantages to a cannibal in terms of increased growth rate and survival. In the field, hatchlings of A. arbustorum consume unhatched sibling eggs as well as eggs from neighbouring batches. In a laboratory experiment, 20 newly hatched sibling snails from each of 24 egg batches were divided into two groups and fed either conspecific eggs or lettuce for 10 days. Growth during this period was recorded, as well as subsequent growth and survival to maturity. During this latter period the animals of both groups were kept under identical conditions and fed on lettuce. Hatchlings fed a cannibalistic diet during their first 10 days of life experienced an increase in wet weight 2 6 times as high as those fed on lettuce. Diet did not affect hatchling survival, but it did influence future survival: 66 6% of the individuals initially fed on eggs attained adulthood compared to 38/0% of those fed on lettuce. Cannibalistic hatchlings tended to complete shell growth more rapidly and thus became mature earlier than non-cannibalistic ones, but the two groups did not differ in adult shell size. Thus, a cannibalistic diet during the hatchling stage will give accelerated growth and higher survival. Key-words: Age at maturity, Arianta arbustorum, egg cannibalism, Gastropoda, growth rate, Pulmonata, size at maturity, survival