Comparison of calcium storage between a Baikalian gastropod and holarctic relatives

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 mu g Ca2+/mu l animal volume (n = 43), and in L. naticoides 865.0 +/- 271.5 mu g Ca2+/mu l (n = 10). Calcium contents in the tissue of B. baicalensis vary between different sampling stations and different sampling dates (fram 9.4 +/- 5.1 (n = 33) to 20.5 +/- 8.4 mu g Ca2+/mg dry weight DW (n = 16)) and are only 1/5-1/10 compared to L. naticoides (88.5 +/- 39.1 mu g Ca2+/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. (C) 2000 Elsevier Science Inc. All rights reserved.