Life Cycle of <i>Perforatella bidentata</i> (Gmelin, 1791) (Gastropoda: Pulmonata: Helicidae)

Selected life history traits of Leptaxis simia (Gastropoda: Hygromiidae) established in the laboratory

Among ten adult specimens of the Madeiran endemic land snail Leptaxis simia kept in the laboratory, a single clutch of 110 eggs was reared, and the mortality, growth and reproductive capacity of hatchlings over a 1240- day period were monitored. Of 70 hatchlings, 34 survived to complete shell growth at around 640 days. Growth was rapid, and mortality high in the early stages; growth slowed and mortality was very low as full size was approached. Snails kept singly failed to lay any eggs. Among those with potential mates, only three clutches were produced, one of which yielded no hatchlings. Clutches were produced at least five months after shell growth was complete. Mortality increased sharply after the onset of sexual maturity, and the oldest snail survived for three and a half years. The apparently very strictly semelparous mode of reproduction, delayed sexual maturity and relatively long period of juvenile growth are discussed in relation to other species, and to the practical problems of rearing potentially endangered species in captivity.

Differences in population dynamics of Bradybaena fruticum (O.F. Müller, 1774) (Gastropoda: Pulmonata: Bradybaenidae) in a submontane and lowland area of Poland

Population dynamics of a meso-hygrophilous helicoid Bradybaena fruticum was studied in SW Poland at two localities with similar habitat but different climatic conditions. Unexpectedly, at the submontane site in Szczytna the growth appeared to be significantly faster than in the lowland site (Wrocław), where the weather conditions varied widely during the whole growing season. In Szczytna the average growth rate was 0.26 whorl/month; 0.36 whorl/month in the fast phase (juveniles from hatching till 5.0 whorls), and 0.07 whorl/month in the slow phase (snails with 5.1 whorls till lip formation). During the whole growing season, the average increment was 4.5 whorls, whereas the maximum was 5.45 whorls. In Wrocław the average growth rate was 0.05 whorl/month; 0.1 whorl/month in the fast phase, and only 0.01 whorl/month in the slow phase. The average growth of juveniles, estimated during two growing seasons, equalled 3.8 whorls; the maximum recorded value was 4.75 whorls. In the winter there was hardly any growth. In earlier studies it was found that at higher altitude the growth rate seems to decrease and therefore appears to be correlated with the thermal regime of the locality. In this study it was established that the weather patterns, like months with drought or occasional flooding, are likely to influence the population dynamics in the lowland population.