title: Effects of the herbicide atrazine on Ambystoma tigrinum metamorphosis: duration, larval growth, and hormonal response.
abstract: We exposed larval tiger salamanders (Ambystoma tigrinum) reared in the laboratory from eggs collected from a prairie wetland in North Dakota to three concentrations of atrazine (0, 75, and 250 micrograms/L) in a static renewal test to determine the pesticide's effect on (1) plasma corticosterone and thyroxine concentrations, (2) larval size, and (3) days-to-stage at stages 2 and 4 of metamorphic climax. We found significant effects of atrazine on each of these response variables. Plasma thyroxine was elevated in both atrazine-exposed groups compared with the control group; plasma corticosterone was depressed in the 75 micrograms/L treatment compared with both the control and 250 micrograms/L treatment. Larvae exposed to 75 micrograms/L atrazine reached stage 4 later but at a size and weight comparable to the control group. By contrast, larvae in the 250 micrograms/L treatment progressed to stage 4 at the same time but at a smaller size and lower weight than larvae in the control group. These results indicate that the herbicide has the potential to influence tiger salamander life history. We present a model consistent with our results, whereby corticosterone and thyroxine interact to regulate metamorphosis of tiger salamanders based on nutrient assimilation and adult fitness.
authors.affiliation: U.S. Geological Survey, Biological Resources Division, Northern Prairie Wildlife Research Center, Saint Paul, Minnesota 55108, USA. dlarson@biosci.cbs.umn.edu
authors.forename: D L
authors.initials: DL
authors.lastname: Larson
authors.forename: S
authors.initials: S
authors.lastname: McDonald
authors.forename: A J
authors.initials: AJ
authors.lastname: Fivizzani
authors.forename: W E
authors.initials: WE
authors.lastname: Newton
authors.forename: S J
authors.initials: SJ
authors.lastname: Hamilton
mesh_terms: D000557:Ambystoma / Q000254:growth & development*; D000818:Animals; D001280:Atrazine / Q000009:adverse effects* / Q000494:pharmacology; D001824:Body Constitution; D003345:Corticosterone / Q000494:pharmacology; D047108:Embryonic Development; D006540:Herbicides / Q000009:adverse effects* / Q000494:pharmacology; D007814:Larva; D008675:Metamorphosis, Biological / Q000187:drug effects*; D013974:Thyroxine / Q000494:pharmacology; D014874:Water Pollutants, Chemical / Q000009:adverse effects* / Q000494:pharmacology
chemical_list: D006540:Herbicides; D014874:Water Pollutants, Chemical; D013974:Thyroxine; D001280:Atrazine; D003345:Corticosterone