Reproductive biology and annual population cycle of Oxyloma retusum (Pulmonata: Succineidae)

摘要

I studied the reproduction and the population turnover of a succineid land snail living by a small lake in central Maryland. The identity of the snail, deduced from its external characteristics and the genitalia, comes closest to Oxyloma retusum (Lea, 1834). The species has a semelparous life cycle. The snails that survive the winter grow and reproduce from late March until the end of June when they reach their maximum size and die off. Their offspring (the spring generation) grow throughout the spring and the summer and reproduce briefl y near the end of August. In the fall, the survivors from the spring generation and their offspring hibernate from November until the end of March. Snails mate by shell-mounting. In 89% of pairs, mating was anatomically reciprocal. During courtship, one snail climbs on the shell of a prospective mate and circles the shell to initiate mating. In mating pairs with a shell length difference of more than 1 mm, the smaller snail was always on top. This suggests that one function of shell-circling during courtship may be to help the top snail judge its potential partner’s size.