Insights into the reproductive activity of Omphiscola (Lymnaea) glabra (Gastropoda: Lymnaeidae) in relation to soil geology in Central France

Transplantations of Omphiscola glabra from granite to marl, or vice versa, between farms known for cases of fasciolosis have shown differences in the maximum shell height of adult snails. To determine whether these differences were due to parasitism, soil geology, or a combination of both factors, four snail populations living on marl or granite were investigated over 12 months to specify the characteristics of egg-laying in spring, and to follow the shell growth of both snail generations. In both types of habitats, the number of egg-masses per adult snail and their size significantly decreased during the 7 weeks of snail egg-laying. During this period, each adult snail on marl laid a mean of 6.4 masses and 93.3 eggs. On granite, the mean values were 5.7 masses and 69.1 eggs, respectively. Two annual generations, the first in spring and the other in autumn, were noted in these habitats. The maximum shell height of adults was different: a mean of 19.8 and 20.5 mm on marl compared with 17.2 and 18.2 mm on granite. Soil geology thus plays a role in the egg-laying and shell growth of O. glabra .