Reproductive biology and population dynamics of an ovoviviparous land snail, Lauria cylindracea (Pupillidae)

The orthurethran land snail Lauria cylindracea is ovoviviparous. We examined its life history in Israel, where it lives in litter of the riparian forest floor, in a cool humid habitat, that has a very stable and predictable temperature. Activity of snails started in winter and continued well into summer with gametogenesis commencing in early winter, after the beginning of the rainy season. In mid winter, all animals showed advanced spermatogenesis, early oogenesis, vitellogenic eggs and a few of the adults contained embryos. By spring and early summer, the gonads were larger, with both mature sperm and up to seven vitellogenic eggs; and up to 100% of the adults contained embryos, usually four 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 embryos. 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 expected from the number of embryos inside the animals, and never exceeded 26% of the population. The juveniles grew until spring and then, as subadults, stopped growth until the following winter. It took a snail two winters to reach reproductive maturity, and the lifespan was about five years. About 30% of the adult snails died in late summer. All individuals throughout the year were euphallic, which is in contrast to the 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 produce only few ova per unit time. Under such conditions, ovoviviparity may be advantageous in that the (few) hatchlings can immediately feed and grow, fight off fungi, cope with brief periods of desiccation and avoid drowning or flooding. In environments subject to frequent flooding, eggs may be retained within the adult until full embryonic development of the kidney. In such an environment of excess water, ovoviviparity may be advantageous.