Combined effects of predatory fish and sublethal pesticide contamination on the behavior and mortality of mayfly nymphs

Abstract

We evaluated the potential interaction of pesticide effect and predatory fish on behavior and mortality of a stream mayfly. Experiments in laboratory stream microcosms compared the activity, drift, and mortality of Baetis mayfly nymphs in the absence of fish with that in the presence of Cape galaxias (Galaxias zebratus), both species inhabiting the same stream environments in the Western Cape of South Africa. These two predator treatments were combined with exposure either to no pesticide or to 0.2 microg/L of the organophosphate insecticide azinphos-methyl (AZP) or 0.2 microg/L of the pyrethroid insecticide fenvalerate (FV). Such pesticide levels are known from transient spraydrift- or runoff-related pesticide input into running waters. Each of the six combinations was replicated six times as 30-min trials during the day and effects were analyzed using 2 x 2 factorial analysis of variance (ANOVA). A single exposure to either fish or pesticide significantly increased the absolute activity of mayflies, measured as number of animals visible on top of stones, and the absolute mayfly drift in the fish treatment and in the FV treatment but did not increase the mortality above 0.8%. The combination of predator presence and sublethal pesticide exposure resulted in a significant increase in the mortality rate, to about 9% in the AZP x fish and 25% in the FV x fish treatment, although the activity and drift rates were not increased compared with the single-stressor treatments. Two-by-two factorial ANOVA and the comparison of expected and measured responses indicated that the mortality resulted from a synergistic interaction of the two stressors. The observed mortality was without exception caused by predation of the fish on drifting mayflies. The relative drift rate in the FV x fish treatment was decreased, again due to a synergistic interaction, which suggests an active drift avoidance reaction of the mayflies exposed to the combined pesticide x fish treatment, in contrast with those exposed just to FV. We conclude that the drift response of mayflies to transient sublethal pesticide exposure results in a synergistically increased adverse effect in the presence of predatory fish.

Effects of predator cues on pesticide toxicity: Toward an understanding of the mechanism of the interaction

“…Interaction effects between predator cues and contaminants on aquatic invertebrates and vertebrates have been observed in laboratory and outdoor mesocosm experiments [8][9][10]25]. Results of the current study support the view that predator stress may interact with pesticides and influence their toxicity in aquatic environments [25].…”

“…Table 4. Weight of evidence summary for evaluating the interaction effects of coexposures to predator cues and pesticides on Ceriodaphnia dubia acute toxicity compared to the pesticides alone fenvalerate [10], endosulfan [24,34], atrazine [24], fenoxycarb [9], carbaryl [26], and glyphosate [37]. In the present study, a relatively new class of pesticide, a neonicotinoid (thiacloprid), was also found to have antagonistic interactions with predator cues on C. dubia survival.…”

“…Within the same experimental system and response variable, these interaction patterns have varied among contaminants [9,10,23,24], suggesting that the process driving these interactions may be related to the mechanism of action of the chemical contaminant. Only a few studies have attempted to explore the mechanisms of the predator cue-contaminant interaction by conducting coexposures between predator cues and multiple chemicals varying in mechanism of toxic action.…”

“…Contaminant toxicity may be modified by environmental and ecological factors such as temperature [1,2], pH [3], resource conditions [4], competition [5], and predation [6,7]. Exposure to predatory cues is a biotic stressor that has received attention recently for its interaction with pesticides on biological responses in both freshwater invertebrate and vertebrate organisms [7][8][9][10].…”

Pressure-Induced Shifts in Trophic Linkages in a Simplified Aquatic Food Web

“…Aquatic animals can react to such pollutants by altering their food source, leading to changes in predation efficiency (Smith and Weis, 1997;Schulz and Dabrowski, 2001), bioturbation (Hinkle-Conn et al, 1998;Hunting et al, 2013) and nutrient cycling (Fleeger et al, 2003). Such alterations in trophic linkages can be regarded as rippling effects in food webs which may result in ecosystemwide effects and subsequently affect ecosystem functioning and the services it provides (Fleeger et al, 2003;Corvalan et al, 2005).…”