Characterization of aspartate transcarbamylase activity from gonads of the soft shell clam, Mya arenaria

Physiological effects of temperature and a herbicide mixture on the soft-shell clam Mya arenaria (Mollusca, Bivalvia)

The aim of the current study was to investigate effects of temperature and a mixture of herbicides on the physiological status of the bivalve Mya arenaria. Bivalves acclimated to two temperatures (7 and 18°C) were exposed for 28 d to 0.01 mg/L of a pesticide formulation containing dichlorophenoxyacetic acid (2,4-D), 2-(2-methyl-4-chlorophenoxy) propionic acid (mecoprop), and 3,6-dichloro-2-methoxybenzoic acid (dicamba). At days 7, 14, and 28, mortality, immune parameters (hemocyte number, phagocytic activity, and efficiency), biomarkers of oxidative stress (catalase [CAT] and superoxide dismutase [SOD] activities and malondialdehyde [MDA] content), the metabolic enzyme cytochrome C oxidase (CCO), a biomarker of pesticide exposure (acetylcholinesterase [AChE]), and the activity of an enzyme related to gametogenesis (aspartate transcarbamylase [ATCase]) were monitored in clam tissues. Gonadosomatic index (GSI), condition factor (CF), and sex were also assessed. In clams acclimated to 7°C, exposure to pesticide enhanced CCO activity and CF and decreased MDA content, hemocyte number, CAT, and SOD activities. In clams kept at 18°C, pesticide effects appeared minor compared with samples kept at 7°C. In bivalves acclimated to 18°C, CCO, SOD, and ATCase activity and MDA content were enhanced, and hemocyte number, CAT, and AchE activities and phagocytosis were suppressed. In samples exposed to pesticides, increased temperature enhanced MDA content and CCO and SOD activity and suppressed hemocyte number and CAT and AchE activity. A gradual sexual maturation was observed in both sexes through experimental time, but females had a higher sensitivity to temperature and pesticides compared to males. Increased temperature altered the ability of the sentinel species Mya arenaria to respond to pesticide exposures. Further work is needed to understand the impacts of increasing temperature on the whole St. Lawrence estuary ecosystem.

Effects of tributyltin and 17β-estradiol on immune and lysosomal systems of the Asian clam Corbicula fluminea (M.)

Freshwater clams Corbicula fluminea were experimentally exposed to a range of tributyltin (TBT) (50, 250 and 500ng Sn/L) and 17β-estradiol (20, 200, 2000ng/L) for 30 days. After 15 and 30 days, phagocytosis activity of haemocytes and lysosomal structural changes in the digestive cells were assayed. 17β-Estradiol exerted a higher inhibition on phagocytosis than tributyltin. This would suggest the existence of estrogen receptors, influencing the immune function. The stereological parameters measured for lysosomal structural changes in animals exposed to tributyltin varied as observed in other studies. Tributyltin is then depurated as other contaminants via digestive cell lysosomal compartment. This experiment emphasized a possible approach on the influence of endocrine disrupting compounds on a hermaphroditic species for environmental surveys.

Sexual maturation and related changes in aspartate transcarbamylase activity of gonad tissues in the soft shell clam (Mya arenaria)

The information on the relation between the gonadal aspartate transcarbamylase (ACTase) activity and the sexual maturation in molluscs is very fragmentary and is still absent in Mya arenaria. The determination of ATCase activity, energy reserves levels and maturation stages were done in gonads of clams. Results showed that the seasonal cycle of storage and utilization of energy reserves in gonads of clams are linked to the bimodal reproduction well known in this bivalve. ATCase activity was high in clams at development and ripe stages, while this activity was low for individuals found in indifferent, spawning or spent stages. This difference can be explained by the fact that during gonad development, gonadal synthetic activity increased following the mitotic events associated to the reproductive cycle. The results presented in this paper have confirmed the link between ATCase activity and gametogenesis in M. arenaria. Further work should be realized in order to assess if ATCase activity could be considered as a potential biomarker to evaluate the disruption of sexual maturation in clams collected in sites such as the St. Lawrence estuary.