Camaenid Land Sanil Reproductive Cycle and Growth Patterns in Semiarid Areas of North Western Australia

Abstract

Dissections of camaenid land snails collected in the Kimberley Region of north-western Australia between 1975 and 1980 reveal a general pattern of sexual maturation. Snails reach half adult shell size in the wet season of their birth, reach adult shell size and become mature males at the end of their second wet season, and function as males at the beginning of their third wet season; the female genitalia mature near the end of this season; and snails function as both males and females in their fourth and subsequent wet seasons. A life span of >8 years is demonstrated. Seasonal genital variation in adults involves: (1) gross size reduction of the apical genitalia during the mid-wet season, which provides maximum space for food storage, thereby allowing survival during aestivation over the long dry season; (2) becoming male active at or shortly before the normal start ofthe wet season at that particular locality; (3) activation of the female system after the first rains of the wet season. Adult shell size is hypothesized to depend upon moisture conditions near the end ofthe snail's second wet season: any early interruption of moisture supply causes growth to stop at a lower whorl count and produces smaller adults; favourable moisture conditions allow extended growth time, with cessation occurring at a higher whorl count, and producing a larger sized adult.