Detecting physiological and pesticide-induced apoptosis in early developmental stages of invasive bivalves

In this study, embryos and early larval stages of two invasive bivalves, the Mediterranean mussel (Mytilus galloprovincialis) and zebra mussel (Dreissena polymorpha), were assayed for physiological apoptosis and stress-induced apoptosis post-exposure to a molluscicide, Bayluscide(A (R)). Physiological apoptosis was measured at 4-h intervals and Bayluscide(A (R)) exposures were 4 h and 24 h beginning at both 30 min post-fertilization and at 24 h post-fertilization. Apoptosis was detected by the TUNEL assay, and apoptotic values were compared for the different stages present. The two bivalves tested for apoptotic cells displayed variations in physiological and stress-induced apoptotic values despite having the same life stage transitions. However, in the majority of exposures, we found that as pesticide concentrations increased, the apoptotic values decreased in the highest concentrations. We suggest that this change to apoptotic inhibition indicates that there is a threshold at which apoptosis can no longer be used as a protective measure against damaged cells. These concentrations that cause changes in apoptotic pattern should be further tested for long-term effects on reproduction and survival. By detecting sub-lethal concentrations that may impair recruitment to the population and the continuation of the life cycle, chemical control of invasive bivalves could be targeted to early life stages and to reduce potential environmental impacts resulting from the higher concentrations required to control adults.