Comparison of calcium storage between a Baikalian gastropod and holarctic relatives

Abstract

In Lake Baikal, extremely thin shells are reported as a typical feature of endemic gastropods. This statement derived only from observations; no experimental data were available up to now. Therefore, we quantitatively investigated the calcium distribution in the endemic prosobranch gastropod Benedictia baicalensis and compared the results with those of Lithoglyphus naticoides, a near relative, non-endemic, palaearctic species. The shell of the endemic mollusc B. baicalensis consists of 94.9±26.0 μg Ca 2+/μl animal volume ( n=43), and in L. naticoides 865.0±271.5 μg Ca 2+/μl ( n=10). Calcium contents in the tissue of B. baicalensis vary between different sampling stations and different sampling dates (from 9.4±5.1 ( n=33) to 20.5±8.4 μg Ca 2+/mg dry weight DW ( n=16)) and are only 1/5–1/10 compared to L. naticoides (88.5±39.1 μg Ca 2+/mg DW ( n=9)). But the values for hemolymph calcium concentration and osmolality in both species are identical ( B. baicalensis: osmolality: 84.4±5.3 mosm/kg ( n=40); hemolymph calcium concentration: 4.6±1.7 mmol/l ( n=40). L. naticoides: osmolality: 85.0±2.0 mosm/kg ( n=8); hemolymph calcium concentration: 5.2±5.0 mmol/l ( n=40).). This is the first experimental study demonstrating, that — besides a similar hemolymph ionic composition — the Baikalian species is characterized by significantly lower calcium storage in shell and tissue than the nearly related non-endemic species.