REPRODUCTIVE-BIOLOGY AND POPULATION-DYNAMICS OF AN OVOVIVIPAROUS LANDSNAIL, LAURIA-CYCLINDRACEA (PUPILLIDAE)

The orthurethran land snail Lauria cylindracea is ovoviviparous. We ex amined its life history in Israel, where it lives in litter of the rip arian forest floor, in a cool, humid habitat, that has a very stable a nd predictable temperature. Activity of snails started in winter and c ontinued well into summer with gametogenesis commencing in early winte r, after the beginning of the rainy season. In mid winter, all animals showed advanced spermatogenesis, early oogenesis, vitellogenic eggs a nd a few of the adults contained embryos. By spring and early summer, the gonads were larger, with both mature sperm and up to seven vitello genic eggs; and up to 100% of the adults contained embryos, usually fo ur per individual. A reproductive adult weighed about 4.5 mg, of which 17-25% was embryo weight. In later summer and autumn, we observed no feeding or reproductive activity, no gametogenesis, and very few embry os. We distinguished three age groups: juveniles, subadults and adults . Juveniles were born in summer by adults having enough moisture to be active, whereas adults on dry leaves appeared to retain their embryos . The number of juveniles was therefore never as high as could be expe cted from the number of embryos inside the animals, and never exceeded 26% of the population. The juveniles grew until spring and then, as s ubadults, stopped growth until the following winter. It took a snail t wo winters to reach reproductive maturity, and the lifespan was about five years. About 30% of the adult snails died in late summer. All ind ividuals throughout the year were euphallic, which is in contrast to t he high frequency of aphally in other pupilloideans. In discussing the adaptive significance of ovoviviparity in Lauria, we note that it is a minute snail, and therefore constrained to low fecundity-it can prod uce only few ova per unit time. Under such conditions, ovoviviparity m ay be advantageous in that the (few) hatchlings can immediately feed a nd grow, fight off fungi, cope with brief periods of desiccation and a void drowning or flooding. In environments subject to frequent floodin g, eggs may be retained within the adult until fun embryonic developme nt of the kidney. In such an environment of excess water, ovoviviparit y may be advantageous.