ORIGINAL ABSTRACT

Glyphosate, a key ingredient in many herbicides, is increasingly present in aquatic systems due to agricultural runoff. High doses of glyphosate cause defects in organisms due to its ability to interfere with physiological processes as an endocrine disruptor. We used the mangrove rivulus fish (Kryptolebias marmoratus) to evaluate the effects of larval exposure to glyphosate on non-target species in aquatic environments. These fish produce genetically identical offspring, allowing us to evaluate phenotypic responses to toxicant exposure while controlling for genetics. We treated newly hatched larvae for 96 h with concentrations of glyphosate on the low and high end of what they would experience in the wild: control (0 mg/L), low (0.01 mg/L), and high (1.1 mg/L), and then measured behavior, morphology, and reproductive traits at 60 and 130 days. We predicted that these amphibious fish exposed to low, environmentally relevant doses would show adaptive emersion behavior to escape poor quality water conditions, and deficits in other traits would be greater with higher glyphosate dosages. We found that low doses (0.01 mg/L) of glyphosate led to lower anxiety (decreased thigmotaxis) and impaired jumping behaviors while high dose exposures to glyphosate resulted in lower activity and lower average egg yield per individual. None of these effects appeared to be adaptive at low or high doses of glyphosate. While deficits in reproductive output scaled with dosage, phenotypic effects were often dosage-specific for each trait. This study demonstrates that even environmentally relevant concentrations of herbicide may be harmful to aquatic organisms and have consequences that persist well into adulthood. Furthermore, given that environmentally relevant concentrations of glyphosate induced deficits in reproductive output, this suggests that glyphosate contamination in natural systems may have population level consequences.