Species-specific responsiveness of four enzymes to endosulfan and predation risk questions their usefulness as general biomarkers

Abstract

General biochemical biomarkers are widely used in current ecotoxicology and may function as early warning signals. We have, however, poor knowledge on how ecologically similar species differ in their biomarker responsiveness and how predation risk may affect these biomarkers, potentially in an interactive way with pesticides. We evaluated this by exposing four corixid water bug species to combinations of endosulfan and predation risk and quantifying the activity of four general enzymatic biomarkers: acetylcholinesterase (AChE), phenoloxidase (PO), catalase (CAT) and superoxidedismutase (SOD). AChE activity was inhibited at an endosulfan concentration of 2 μg l(-1) and this did not differ significantly among species. Predation risk inhibited AChE activity with the same magnitude as endosulfan in one species, S. striata. Reduction in the investment of immune function following pesticide exposure, as measured by the activity of PO, was only observed in C. coleoptrata at 8 μg l(-1) while we observed an increase of PO levels in S. striata. Overall, PO was suppressed under predation risk at 8 μg l(-1) endosulfan. For SOD we observed a pesticide-induced increase across all species under predation risk, while for CAT the pesticide-induced increase was only present without predation risk. These results indicate that even within this group of ecologically similar and closely related species opposing biomarker responses may exist, as observed for PO. Effects of predation risk on all four enzymes, at a similar magnitude as the pesticide effects, further question their usefulness as general biomarkers.

Stronger effects of Roundup than its active ingredient glyphosate in damselfly larvae

“…We measured the activity of AChE on the heads using a for insects modified version of the protocol of Ellman (Jensen et al 1997). This enzyme has an important function in the nervous system by catalysing the breakdown of acetylcholine and higher activity levels have been shown to be positively related to escape swimming speed (Trekels et al 2012;Bonansea et al 2016). We homogenized the heads in 250 µl PBS and after centrifugation we used the supernatant for the analysis.…”

Combined effects of larval exposure to a heat wave and chlorpyrifos in northern and southern populations of the damselfly Ischnura elegans

“…PO activity can increase, decrease or remain constant) depending on the studied freshwater invertebrate and the tested contaminants (e.g. Campero et al, 2008;Lilley et al, 2012;Trekels et al, 2012;Janssens and Stoks, 2013a). Lilley et al (2012) documented an increase in PO activity (humoral immunity) in Chironomus riparius midge larvae exposed to tributyltin and explained this as a compensatory response for the reduced cellular immunity.…”

Synergistic effects between pesticide stress and predator cues: Conflicting results from life history and physiology in the damselfly Enallagma cyathigerum

“…Several studies demonstrated synergistic effects between pesticide exposure and predator cues for life history traits such as mortality and growth rate (e.g., Releya and Mills, 2001;Campero et al, 2007;Trekels et al, 2011). Yet, such synergistic effects on life history are not always detected (e.g., Coors and De Meester, 2008;Jansen et al, 2011) and physiological traits have been largely ignored (but see Campero et al, 2007;Trekels et al, 2012). Three types of neglected physiological traits are especially relevant to consider in the context of synergistic interactions between exposure to pesticides and predator cues as these types are related to fitness and are known to be influenced by both stressors separately.…”