Oviposition site selection: Pesticide avoidance by gray treefrogs

Abstract

Effects of glyphosate-formulated herbicides on nontarget organisms have received much recent attention. Although previous studies have explored the effects of pesticides on growth, development, and mortality of various amphibian species, no studies have tested the potential effects of herbicides on oviposition site selection by amphibians. Recent studies have found that a combination of pesticide and predatory cues lead to significantly increased mortality of tadpoles of several anuran species relative to that caused by pesticide alone. In the present study, I tested two hypotheses: First, adult gray treefrogs avoid oviposition sites based on the presence of glyphosate formulation (Roundup). Second, pesticide avoidance is manifested to a greater degree when combined with predatory cues. In the spring of 2006, I conducted an outdoor experiment using artificial ponds by setting up four treatments: Predatory fish cue, Roundup (2.4 mg glyphosate acid equivalent [a.e.]/L), a combination of predatory fish cue + Roundup, and a control. This experiment was designed to assess oviposition site choice among the four treatments by gray treefrogs based on the number of eggs laid in each treatment. Gray treefrogs avoided oviposition in pools contaminated with fish cue and/ or Roundup and placed the significant majority of their eggs in control pools, which suggests that breeding adults may be able to prevent lethal exposure of herbicide to their offspring through oviposition site selection. The present study provided the first evidence that the concentration of herbicide that is expected to be found in the field potentially alters oviposition site choice by amphibians. However, the concentration of 2.4 mg a.e./L is unlikely ubiquitous in nature. Thus, the further investigation of environmental relevancy of this finding is critical.

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

“…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.…”

Effects of an environmentally relevant temporal application scheme of low herbicide concentrations on larvae of two anuran species

“…Prolonged and shortened metamorphosis as well as reduced body indices were seen (Bridges, 2000;Howe et al, 2004;Cauble and Wagner, 2005;Williams and Semlitsch, 2010). Indirect effects of pesticide use included avoidance of contaminated breeding sites (Takahashi, 2007;Vonesh and Buck, 2007; but see . Exposure risks and adverse effects of pesticides are specific in three ways.…”

Pesticide alters habitat selection and aquatic community composition

“…Furthermore, two recent studies show that pesticides can alter oviposition site selection in some amphibians. Takahashi (2007) showed that gray treefrogs (Hyla chrysoscelis/ versicolor) completely avoid pools treated with the glyphosphate-formulated herbicide Roundup. Similarly, Vonesh and Buck (2007) show in a series of experiments that the insecticide Sevin and its active ingredient, carbaryl, also reduce oviposition in gray treefrogs across several spatial and temporal scales.…”