Effects of metals exposure on morphological and histological structure of the digestive gland in native and invasive clams in the Paraná de las Palmas River (Buenos Aires, Argentina)

Corbicula fluminea is an aggressive invasive species that has successfully colonized aquatic habitats worldwide, producing changes in natural environments and impacting endemic populations. As disturbed environments may favor the adaptive success of exotic species over native ones, we studied the fitness response of two freshwater bivalves, invasive C. fluminea and native Diplodon delodontus, to the presence of metals in the Parana de la Palmas River. To assess the health status of both species, we analyzed morphological and histological alterations in the digestive gland and their relation to metal concentrations in this organ and in the water. Water and specimens sampling took place in the first section of the delta of the Parana River in June and September. Most metal concentrations increased in the river, although in the digestive gland only iron in D. delodontus and nickel and zinc in C. fluminea increased seasonally. Digestive gland factor and hepatosomatic index indicated higher values in C. fluminea in both periods. Despite histological analysis showing a decrease in atrophic tubules frequency in both species, which was followed by histomorphometric parameters of the epithelium and lumen of the digestive tubules, C. fluminea exhibited a greater physiological capacity for metal metabolism and recovery. These results suggest that the physiological characteristics of the Asian clam C. fluminea, combined with its reproductive efficiency and broad dispersal capacities, could explain its invasive dispersal competence over the D. delodontus in the disturbed environmental conditions observed in the Parana de las Palmas River.