Abstract
Interactions between pollutants and suboptimal environmental conditions can have severe consequences for the toxicity of pollutants, yet are still poorly understood. To identify patterns across environmental conditions and across fitness-related variables we exposed Enallagma cyathigerum damselfly larvae to the pesticide chlorpyrifos at two food levels or at two temperatures and quantified four fitness-related variables (larval survival, development time, mass at emergence and adult cold resistance). Food level and temperature did not affect survival in the absence of the pesticide, yet the pesticide reduced survival only at the high temperature. Animals reacted to the pesticide by accelerating their development but only at the high food level and at the low temperature; at the low food level, however, pesticide exposure resulted in a slower development. Chlorpyrifos exposure resulted in smaller adults except in animals reared at the high food level. Animals reared at the low food level and at the low temperature had a higher cold resistance which was not affected by the pesticide. In summary our study highlight that combined effects of exposure to chlorpyrifos and the two environmental conditions (i) were mostly interactive and sometimes even reversed in comparison with the effect of the environmental condition in isolation, (ii) strongly differed depending on the fitness-related variable under study, (iii) were not always predictable based on the effect of the environmental condition in isolation, and (iv) bridged metamorphosis depending on which environmental condition was combined with the pesticide thereby potentially carrying over from aquatic to terrestrial ecosystems. These findings are relevant when extrapolating results of laboratory tests done under ideal environmental conditions to natural communities.
Highlights
The widespread occurrence of interactions between stressors is an important threat to biodiversity [1]
We investigate the combined effect of exposure to the pesticide chlorpyrifos and suboptimal environmental conditions during the larval stage on a set of fitness-related variables measured in the larval stage and across metamorphosis in the damselfly Enallagma cyathigerum
Survival in the presence of chlorpyrifos seemed lower at the low food level than at the high food level there was no significant pesticide-by-food interaction (x21 = 0.13, p = 0.71)
Summary
The widespread occurrence of interactions between stressors is an important threat to biodiversity [1]. Many studies have shown that the effects of pollutants may be magnified under suboptimal environmental conditions such as food shortage and suboptimal temperatures (reviewed in [3,4,5]) This is important to consider for ecological risk assessment, as in nature organisms often face suboptimal conditions while ecotoxicological studies typically expose test organisms under optimal environmental conditions [4,5,6]. Interactions between pollutants and suboptimal environmental conditions can have severe consequences for the toxicity of pollutants and are widely documented (reviewed in [3,4,5]), their occurrence and fitness implications are still poorly understood and no specific predictive modeling framework for their combined impact has been developed [4,5,7], partly because most empirical ecotoxicological studies considered only combinations with a single environmental variable and focused on one or two fitness-related variables. Some of them have documented interactive carry-over effects in the adult stage (e.g. [13,14]), while others did not (e.g. [15,16])
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