Response of the nonbiting midge Chironomus riparius to multigeneration toxicant exposure.

The ability of the nonbiting midge Chironomus riparius to withstand long-term toxicant exposure has been attributed to genetic adaptation. Recently, however, evidence has arisen that supports phenotypic plasticity. Therefore, the present study aimed to investigate if Chironomus riparius indeed copes with prolonged toxicant exposure through phenotypic plasticity. To this purpose, we performed a multigeneration experiment in which we exposed C. riparius laboratory cultures for nine consecutive generations to two exposure scenarios of, respectively, copper, cadmium, and tributyltin. Total emergence and mean emergence time were monitored each generation, while the sensitivity of the cultures was assessed at least every third generation using acute toxicity tests. We observed that the sublethally exposed cultures were hardly affected, while the cultures that were exposed to substantially higher toxicant concentrations after the sixth generation were severely affected in the eighth generation followed by signs of recovery. A marginal lowered sensitivity was only observed for the highly exposed cadmium culture, but this was lost again within one generation. We conclude that C. riparius can indeed withstand long-term sublethal toxicant exposure through phenotypic plasticity without genetic adaption.