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Does size really matter? The effect of atrazine and competition on growth

Does size really matter? The effect of atrazine and competition on growth in Ambystoma mexicanum (the axolotl) Francis Drew Henry and Christopher K. Beachy Department of Biology and Amphibian Growth Project Minot State University, Minot ND, 58707. Why Atrazine?.

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Does size really matter? The effect of atrazine and competition on growth

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  1. Does size really matter? The effect of atrazine and competition on growth in Ambystoma mexicanum (the axolotl) Francis Drew Henry and Christopher K. Beachy Department of Biology and Amphibian Growth Project Minot State University, Minot ND, 58707

  2. Why Atrazine? • #1 herbicide used in the United States and most likely the world • applied in large amounts during spring run-off • detected in water-sheds where atrazine has never been used • known endocrine disruptor

  3. ENDOCRINE DISRUPTION ATRAZINE --Post application (Spring) runoff can be > 20 ppb --typical surface and groundwater concentrations at other times during other times of the year, 0.001 to 1.0 ppb --3 ppb EPA standard for drinking water Males exposed to 0.1 ppb have lowered testosterone, elevated estrogen, and intersex gonads Xenopus laevis Hayes et al, 2002, PNAS Why Atrazine? Study 1

  4. Why Atrazine? Studies 2, 3 and 4 • Larson et al 2003 - Atrazine on Ambystoma tigrinum • Sih et al 2003 – Atrazine on Ambystoma barbouri • Beachy et al, in prep. – Atrazine on Ambystoma maculatum All show a decrease in metamorphic mass. Suggests a reduced growth rate due to atrazine Is it actually growth rate (PIT) or is it decrease in size at metamorphosis (THY)?

  5. HYP gh (growth hormone) prl (prolactine) PIT THY Gonads t4, t3 (metamorphosis) Why Atrazine? Hayes Larson, Sih, and Beachy HYP gh (growth hormone) prl (prolactine) PIT estrogens testosterone Showed decrease in metamorphic mass and possibly PIT dependence Showed decrease testosterone In males Atrazine had access to the entire pathway, and all studies had an Endpoint which was metamorphosis. But where are it’s effects?

  6. HYP gh (growth hormone) prl (prolactine) PIT THY t4, t3 (metamorphosis) Why Atrazine? Henry “metamorphic barrier” Used a paedomorphic species (axolotl) to eliminate thyroid from the equation. Atrazine does not have access to the entire pathway. Will there still be a significant decrease in growth due to atrazine?

  7. Why Competition? • Environmental stressor • Interaction with endocrine disruptors • Density dependent • Toxicological designs often lack ecologically relevant context

  8. We hypothesized that atrazine, as an endocrine disruptor, would effect growth, development, and gene expression in Ambystoma mexicanum (the axolotl salamander)

  9. Experimental Design This table represents the 9 treatments in one block 1 2 1 Block 3 4 5 • 195 salamanders • 9 treatments in each of 5 separate blocks • Contained within one cooler • Each box contained same amount of water and received same aliquot of food • Analysis of mean body mass over 4 time periods

  10. Background • Metamorphosis and growth are thought to be interrelated and growth • is thought to be PIT dependent • Fast growth leads to earlier metamorphosis • Use metamorphic mass to infer growth effects

  11. Results MANOVA (mass, svl, surv) Source Atrazine Density Atraz*Dens Wilksλ .837 .204 .831 Df 6,58 6,58 12,77 F .901 11.722 .465 P .501 <.001 .929 ANOVA (svl) Source Atrazine Density Atraz*Dens error df 2 2 4 31 MS .0048 .0925 .0031 .0046 F 1.04 19.857 .672 P .366 <.001 .617

  12. Results Atrazine x Growth mg -No significant atrazine effect shown by genomics

  13. Results Density x Growth mg

  14. HYP gh (growth hormone) prl (prolactine) PIT THY Gonads t4, t3 (metamorphosis) Why Atrazine? Hayes Larson, Sih, and Beachy HYP gh (growth hormone) prl (prolactine) PIT estrogens testosterone Showed decrease in metamorphic mass and possibly PIT dependence Showed decrease testosterone In males Atrazine had access to the entire pathway, and all studies had an Endpoint which was metamorphosis. But where are it’s effects?

  15. HYP gh (growth hormone) prl (prolactine) PIT THY t4, t3 (metamorphosis) Why Atrazine? Henry “metamorphic barrier” Used a paedomorphic species (axolotl) to eliminate thyroid from the equation. Will growth still be affected? Atrazine does not have access to the entire pathway. There was no significant decrease in growth due to atrazine, suggesting that growth control may be further downstream, possibly at the gonadal or thyroid level.

  16. Conclusion • What we know • atrazine effect • density effect • What we plan to know • Atrazine effect at higher density level through genomics • Gonadal inspections – linked to human reproduction • Fat body inspections – linked to human obesity • Ambystoma gene chips as bio-monitoring system

  17. Thanks to: Janel Richter Ken Cabarle Claude Ouedraogo Heather Modrow Jeremiah Johnson Karen Pocha-Melby Biology Department and The Amphibian Growth Project

  18. Questions?

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