Does size really matter

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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
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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

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Why Atrazine?
Study 1
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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)?
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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 its effects?
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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?
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Why Competition?

• Environmental stressor
• Interaction with endocrine disruptors
• Density dependent
• Toxicological designs often lack ecologically
  relevant context

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

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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

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Results
MANOVA (mass, svl, surv)
Source Atrazine Density AtrazDens
Wilks ? .837 .204 .831
Df 6,58 6,58 12,77
F .901 11.722 .465
P .501 lt.001 .929
ANOVA (svl)
Source Atrazine Density AtrazDens error
df 2 2 4 31
MS .0048 .0925 .0031 .0046
F 1.04 19.857 .672
P .366 lt.001 .617
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Results
Atrazine x Growth
mg
-No significant atrazine effect shown by genomics
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Results
Density x Growth
mg
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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 its effects?
15
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.
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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

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