title: Effects of glyphosate-based herbicides on survival, development, growth and sex ratios of wood frog (Lithobates sylvaticus) tadpoles. II: agriculturally relevant exposures to Roundup WeatherMax® and Vision® under laboratory conditions.
abstract: Glyphosate-based herbicides are currently the most commonly used herbicides in the world. They have been shown to affect survival, growth, development and sexual differentiation of tadpoles under chronic laboratory exposures but this has not been investigated under more environmentally realistic conditions. The purpose of this study is (1) to determine if an agriculturally relevant exposure to Roundup WeatherMax®, a relatively new and understudied formulation, influences the development of wood frog tadpoles (Lithobates sylvaticus) through effects on the mRNA levels of genes involved in the control of metamorphosis; (2) to compare results to the well-studied Vision® formulation (containing the isopropylamine salt of glyphosate [IPA] and polyethoxylated tallowamine [POEA] surfactant) and to determine which ingredient(s) in the formulations are responsible for potential effects on development; and (3) to compare results to recent field studies that used a similar experimental design. In the present laboratory study, wood frog tadpoles were exposed to an agriculturally relevant application (i.e., two pulses) of Roundup WeatherMax® and Vision® herbicides as well as the active ingredient (IPA) and the POEA surfactant of Vision®. Survival, development, growth, sex ratios and mRNA levels of genes involved in tadpole metamorphosis were measured. Results show that Roundup WeatherMax® (2.89 mg acid equivalent (a.e.)/L) caused 100% mortality after the first pulse. Tadpoles treated with a lower concentration of Roundup WeatherMax® (0.21 mg a.e./L) as well as Vision® (2.89 mg a.e./L), IPA and POEA had an increased condition factor (based on length and weight measures in the tadpoles) relative to controls at Gosner stage (Gs) 36/38. At Gs42, tadpoles treated with IPA and POEA had a decreased condition factor. Also at Gs42, the effect on condition factor was dependent on the sex of tadpoles and significant treatment effects were only detected in males. In most cases, treatment reduced the normal mRNA increase of key genes controlling development in tadpoles between Gs37 and Gs42, such as genes encoding thyroid hormone receptor beta in brain, glucocorticoid receptor in tail and deiodinase enzyme in brain and tail. We conclude that glyphosate-based herbicides have the potential to alter mRNA profiles during metamorphosis. However, studies in natural systems have yet to replicate these negative effects, which highlight the need for more ecologically relevant studies for risk assessment.
authors.affiliation: Centre for Advanced Research in Environmental Genomics (CAREG), Department of Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada. Electronic address: c.lanctot@cqu.edu.au.
authors.forename: C
authors.initials: C
authors.lastname: Lanctôt
authors.affiliation: Centre for Advanced Research in Environmental Genomics (CAREG), Department of Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada. Electronic address: laianavarromartin@gmail.com.
authors.forename: L
authors.initials: L
authors.lastname: Navarro-Martín
authors.affiliation: Centre for Advanced Research in Environmental Genomics (CAREG), Department of Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada. Electronic address: courtney.j.robertson@gmail.com.
authors.forename: C
authors.initials: C
authors.lastname: Robertson
authors.affiliation: Fisheries and Oceans Canada, Freshwater Institute, Winnipeg, Manitoba R3T 2N6, Canada. Electronic address: brad.park@dfo-mpo.gc.ca.
authors.forename: B
authors.initials: B
authors.lastname: Park
authors.affiliation: Environment Canada, Atlantic Laboratory for Environmental Testing, Moncton , New Brunswick E1A 3E9, Canada. Electronic address: paula.jackman@ec.gc.ca.
authors.forename: P
authors.initials: P
authors.lastname: Jackman
authors.affiliation: Environment Canada, National Wildlife Research Center, Carleton University, Ottawa, Ontario K1A 0H3, Canada. Electronic address: bruce.pauli@ec.gc.ca.
authors.forename: B D
authors.initials: BD
authors.lastname: Pauli
authors.affiliation: Centre for Advanced Research in Environmental Genomics (CAREG), Department of Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada. Electronic address: trudeauv@uottawa.ca.
authors.forename: V L
authors.initials: VL
authors.lastname: Trudeau
mesh_terms: D000818:Animals; D005260:Female; D005998:Glycine / Q000031:analogs & derivatives* / Q000633:toxicity; D006540:Herbicides / Q000633:toxicity; D007814:Larva / Q000187:drug effects / Q000254:growth & development; D008297:Male; D008675:Metamorphosis, Biological / Q000187:drug effects; D011898:Ranidae / Q000254:growth & development / Q000502:physiology*; D012744:Sex Ratio; D014874:Water Pollutants, Chemical / Q000633:toxicity; D000097797:Glyphosate
chemical_list: D005998:Glycine; D006540:Herbicides; D014874:Water Pollutants, Chemical; D000097797:Glyphosate
keywords: Amphibian; Endocrine disruptor; Glyphosate-based herbicide; Metamorphosis; Sex-ratio; mRNA