Abstract
Marine molluscs are ecologically and economically important group of organisms that survive in the challenging environments of different oceanic zones. Of all the classes of the phylum Mollusca, gastropods have radiated into marine, freshwater and terrestrial habitats, successfully adapting themselves to thrive in changing environmental conditions. Hence, marine gastropods can be considered as an ideal system to study stress adaptation. In order to withstand the constant fluctuations in temperature, salinity and shifts in oxygen concentration of the intertidal zone, the gastropods inhabiting here rely on a modified and adaptive energy metabolism. The same is applicable for gastropods living in the deep sea environment, which is characterized by high hydrostatic pressure, low oxygen concentrations and abundance of heavy metals. Therefore, survival of these organisms may be correlated to their adaptive mitochondrial genome which serves as the principal site for energy metabolism and production in the cell. Here, we estimated selection pressure acting on the mitochondrial protein-coding genes of 13 intertidal and 2 deep sea gastropods based on site and branch-site specific models. The results exhibited higher number of sites under diversifying selection for the mitochondrial protein-coding genes of intertidal gastropods compared to deep sea species. Overall, this study focusses on the adaptive mitogenome evolution of marine gastropods for survival in the dynamic environments of the intertidal zone as well as deep sea.