Season- and sex-related variation in mucin secretions of the striped Venus clam, Chamelea gallina (Linnaeus, 1758) (Bivalvia: Veneridae)

Abstract

Abstract An in situ analysis of mucin secretions along the annual cycle was performed on the striped Venus clam, Chamelea gallina. Individuals of both sexes from an exploited stock of Margherita di Savoia (Southern Adriatic Sea, Central Mediterranean Sea) were made in June 2020 and 2021, and in January 2021 and 2022, representative of summer and winter seasons, respectively. Tissues from the foot and the gills were analyzed for histochemical and lectin-histochemical analyses. Staining with Periodic Acid-Schiff, Alcian Blue pH 2.5 and High-Iron-Diamine indicated that mucins from both the foot and the gills were acidic, mostly sulfated. Lectin-binding analyses with PNA, SBA, WGA, LTA, UEA-I, AAA, SNA, MAA-II and ConA indicated the presence of N-acetyl-glycosaminylated, mannosylated and fucosylated residuals in the saccharidic chains. In the gills, the amount of acidic and glycosaminylated residuals was higher in summer in both sexes, whereas fucosylation was similar along the sampling period and mannosylation was never observed. In the foot, both surface epithelial and subepidermal secreting cells increased sulfation in winter in males, but not in females. Glycosaminylation and fucosylation were observed only in the surface cells of males. Mannosylated residuals were observed in all the foot cell types in both sexes. It is hypothesized that the observed qualitative and quantitative variations in mucin secretion is linked to the reproductive cycle. Highlights The mucocytes present in the gill filaments of the clam produce an acid mucus, with sulfate residues and N-acetylglucosamine and fucose chains. In the foot, the subepithelial mucocytes produce an acidic, sulfate secretion with mannosylated residuals. The foot epithelium shows an acidic, sulfated mucus composition with N-acetylglucosamine, fucose and mannose chains. The results show that males have greater variability in mucus composition. The observed variation could be related to different energy allocation between sexes in the development of gametes.