Low Levels of the Herbicide Atrazine Alter Sex Ratios and Reduce Metamorphic Success in Rana pipiens Tadpoles Raised in Outdoor Mesocosms

• Published in: Environmental health perspectives Vol. 118; no. 4; pp. 552 - 557
• Main Authors: Langlois, Valérie S., Carew, Amanda C., Pauli, Bruce D., Wade, Michael G., Cooke, Gerard M., Trudeau, Vance L.
• Format: Journal Article
• Language: English
• Published: Research Triangle Park, NC National Institute of Environmental Health Sciences 01.04.2010; US Department of Health and Human Services
• Subjects: Amphibians; Animal, plant and microbial ecology; Animals; Applied ecology; Atrazine; Atrazine - toxicity; Biological and medical sciences; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on vertebrates; Female; Female animals; Fundamental and applied biological sciences. Psychology; Gene expression; Health aspects; Herbicides - toxicity; Larva - drug effects; Larva - physiology; Liver; Male; Male animals; Medical sciences; Messenger RNA; Metamorphosis; Metamorphosis, Biological - drug effects; Pesticides, fertilizers and other agrochemicals toxicology; Rana pipiens - physiology; Reptilia. Amphibia; Reverse Transcriptase Polymerase Chain Reaction; Sex Ratio; Tadpoles; Toxicology; Canada; RNA-directed DNA polymerase; Toxicity; Amphibia; Estrogen synthase; gonadal development; real-time RT-PCR; Outside air; Health and environment; Enzymatic activity; enzyme activity; North; metamorphosis; Reverse transcription polymerase chain reaction; amphibians; Feminization; aromatase; Enzyme; Frog; Transferases; Low dose; Pesticides; Animal origin; Rana pipiens; Salientia; Real time; Herbicide; Sex ratio; Nucleotidyltransferases; Vertebrata; 5β-reductase; Animal; Triazine derivatives; Northern leopard frog; Ranidae; Oxidoreductases; Atrazine; Reductase
• ISSN: 0091-6765; 1552-9924
• DOI: 10.1289/ehp.0901418

Background: There are conflicting reports regarding the effects of atrazine (ATZ) on amphibian development. Therefore, further studies are needed to examine the potential mechanisms of action of ATZ in amphibians. Objectives: Our aim in this study was to determine whether low concentrations of ATZ affect gonadal development and metamorphosis in the Northern leopard frog, Rana pipiens. Methods: Tadpoles were exposed in outdoor mesocosms to nominal concentrations of 0.1 and 1.8 μg/L of formulated ATZ from Gosner stage 27 (G27) to metamorphic climax (G42). Exposure to 17α-ethinylestradiol (EE₂; 1.5 μg/L) provided a positive control for induction of testicular oocytes in males. Endocrine-related gene expression and gonadal histopathology were examined at G42 and in a subset of premetamorphic G34 tadpoles that failed to metamorphose. Results: Gonadal gross morphology revealed that the 1.8-μg/L ATZ treatment produced 20% more females compared with the control. Histologic analysis revealed that 22% of EE₂-treated males had testicular oocytes, whereas none were observed in any animals from the control or either ATZ groups. ATZ increased brain estrogen receptor α mRNA to 2.5 times that of the control at premetamorphosis and altered liver levels of 5β-reductase activity at metamorphosis. In contrast, brain aromatase mRNA level and activity did not change. ATZ treatments significantly reduced metamorphic success (number of animals reaching metamorphosis) without affecting body weight, snout—vent length, or age at metamorphosis. Gene expression analysis indicated that ATZ decreased the expression of deiodinase type 3 in the tail at premetamorphosis. Conclusions: Our study indicates that exposure to low concentrations of ATZ in experimental mesocosms alters gonadal differentiation and metamorphosis in developing R. pipiens.