Glyphosate-environmental variables interaction: How does it affect the parasite Chordodes nobilii?

Abstract

The worldwide used herbicide Glyphosate can interact with environmental variables, but there is limited informationon the influence of environmental stressors on its toxicity. Environmental changes could modifyglyphosate effects on non-target organisms, including parasites such as gordiids. The freshwater microscopic larvaeof the gordiid Chordodes nobilii are sensitive to several pollutants and environmental variables, but their combinedeffect has not been evaluated yet. The aim of this study was to evaluate the impact of temperature, pH andexposure time on the toxicity of Glyphosate to C. nobilii larvae. A protocol was followed to evaluate the infectivityof larvae treated with factorial combinations of concentration (0 and 0.067 mg/L), exposure time (24 and48 h), temperature (18, 23 and 28 °C), and pH (7, 8 and 9). The reference values were 23 °C, pH 8 and 48 h. Theinteraction effect on the infectivity of gordiid larvae was assessed post-exposure using Aedes aegyptii larvae ashost. Results were evaluated using GLMM, which does not require data transformation. The modeling results revealedthree highly significant triple interactions. Glyphosate toxicity varied depending on the combination ofvariables, with a decrease being observed after 24 h-exposure at pH 7 and 23 °C. Glyphosate and 28 °C combinationled to slightly reduced infectivity compared to temperature alone. This study is the first to report the combinedeffects of glyphosate, temperature, pH and time on a freshwater animal. It demonstrates that a specificcombination of factors determines the effect of glyphosate on a non-target organism. The potential use of C. nobillias a bioindicator is discussed. In the context of global warming and considering that the behavioral manipulationof terrestrial hosts by gordiids can shape community structure and the energy flow through food webs, ourresults raise concerns about possible negative effects of climate change on host-parasite dynamics.