On generation of statoconia in gravireceptors of mollusks

Two models of development of statoconia in the statocyst of mollusks, based on the experimental data [Hearing Res. 49 (1990) 63; Hearing Res. 109 (1997) 125; Hearing Res. 109 (1997) 109;] are proposed. The purpose of the present work is to apply mathematical modeling to the analysis of mechanisms of statoconia formation and generation by supporting cells at the stage of their accumulation in the cyst lumen. In the case of Aplysia californica, it is not clear whether there is a temporal change of statoconia due to their growth in the cyst lumen similar to that in Biomphalaria, or whether the growth of statoconia occurs in supporting cells before they get into the cyst lumen. This question has to do with a more general and insufficiently investigated problem of the mechanisms of statoconia evolution during their stage of accumulation. This is related to A. californica as well as to the initial phase of development of Biomphalaria glabrata. This problem is of practical importance because the majority of experiments related to the study of the effects of altered gravity on the development of gravireceptors in the two mollusks A. californica and B. glabrata deals with the initial phase of statoconia development. It is assumed that two main processes determine the evolution of statoconia in developing mollusks: generation of new statoconia by growing supporting cells and growth of statoconia sizes in the cyst lumen. Analysis of experimental data related to the generation of statoconia in Aplysia and comparison of these data with the results of modeling of accumulation of statoconia suggest that the basic mechanism of evolution of size distribution of statoconia in Aplysia is growth of embryonic statoconia in supporting cells, that follows the growth of animal size. Thus, the large sizes of statoconia are determined by their development within supporting cells rather than by their growth in the cyst lumen. Analysis of the data concerning Biomphalaria allows us to assume that distribution of supporting cells which generate statoconia also varies. The results of modeling of evolution of statoconia specify necessary additional experiments, which are required to refine and test the model.