Differential Effects of Malathion and Nitrate Exposure on American Toad and Wood Frog Tadpoles

Abstract

Organisms living in aquatic ecosystems are increasingly likely to be exposed to multiple pollutants at the same time due to the simultaneous use of several pesticides and fertilizers. We examined the single and interactive effects of environmentally realistic concentrations of nitrate and malathion on two species of tadpoles common in agricultural regions of the United States-the American Toad (Bufo americanus) and the Wood Frog (Rana sylvatica)-using a fully factorial mesocosm experiment that crossed four concentrations of malathion ranging from 0 to 1000 μg/l and two concentrations of nitrate (0 or 8 mg/l). In both B. americanus and R. sylvatica, malathion delayed metamorphosis compared to controls, even at the lowest concentration of malathion. Malathion did not affect survivorship in either species. B. americanus metamorphs were smaller in malathion treatments, whereas R. sylvatica were larger in malathion treatments. Nitrate did not affect survivorship or metamorph size in either species, but did accelerate time to metamorphosis in R. sylvatica. The interaction between nitrate and malathion had no effects in B. americanus and had no effect on R. sylvatica survivorship or metamorph size. However, in the 250 μg/l and 500 μg/l malathion treatments, nitrate reduced the negative effect of malathion on time to metamorphosis in R. sylvatica such that there was little if any delay in metamorphosis compared to the controls in these treatment combinations. This observation suggests that the presence of nitrate might ameliorate the effects of malathion on R. sylvatica. Our results suggest that malathion could have significant effects on anuran populations and communities and that nitrate might potentially mediate such effects in some species.

Detecting Amphibians in Agricultural Landscapes Using Environmental DNA Reveals the Importance of Wetland Condition

“…Highly productive wetlands are likely to provide abundant food supplies for frog larvae and adults, and some evidence suggests that eutrophication may increase tadpole growth in this way (Belden 2006;Johnson et al 2007). None of the wetlands had dissolved nitrogen (nitrate) levels sufficiently high to cause tadpole mortality or sublethal effects (Marco et al 1999;Camargo et al 2005;Krishnamurthy et al 2008;Smith et al 2011). All wetland nitrate concentrations observed in the present study were also below the recommended maximum value of 2.0 mg/L NO 3 -N for sensitive freshwater species (Camargo et al 2005).…”

Effects of combinations of malathion and cypermethrin on survivability and time of metamorphosis of tadpoles of Indian cricket frog (Fejervarya limnocharis)

“…[6] Organophosphate pesticides (e.g., malathion, methyl parathion) are known to cause negative effects on growth, development, metamorphosis and behaviour of the tadpoles. [6,[9][10][11][12][13]19,20] [21] and is widely considered as an ideal insecticide in agriculture. [22] Pyrethroids are highly toxic to non-target species including amphibians and produce negative effects on tadpoles and adult frogs.…”

Effects of Agricultural Stressors on Growth and an Immune Status Indicator in Wood Frog (Lithobates sylvaticus) Tadpoles and Metamorphs

“…Given the low total concentrations of pesticides in these wetlands, it is unlikely Accepted Article that they alone are the sole factor in causing reduced tadpole mass. Mixtures of pesticides with other agricultural contaminants, like fertilizers, can have varying effects on tadpole growth (Relyea 2004;Mann et al 2009;Smith et al 2011). Further, there may be other factors contributing to the observed reduction in tadpole mass at wetlands with higher pesticide detections, including co-occurrence of unmeasured pesticides (e.g., glyphosate; Relyea 2005;Mann et al 2009) or eutrophication.…”

“…For pond‐breeding amphibians, natural processes that affect population growth rates are influential during the larval and juvenile stages and include factors such as predation, food quantity, water temperature, and the likelihood of the water body to desiccate prematurely (Semlitsch and Bridges 2005). The addition of anthropogenic habitat alteration and climate change puts greater stress on this life stage, when successful metamorphosis is critical to adult survival and fecundity (Relyea 2004; Smith et al 2011; Todd et al 2011). A primary threat to amphibians is pollution (Hopkins 2007; Wake and Vredenberg 2008; Lesbarrères et al 2014).…”