Download Why Atrazine? - Department of Biology

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?
• #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
Why Atrazine?
Study 1
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?
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)?
Why Atrazine?
Hayes
Larson, Sih, and Beachy
HYP
PIT
HYP
gh (growth hormone)
prl (prolactine)
Gonads
estrogens
testosterone
Showed decrease testosterone
In males
PIT
gh (growth hormone)
prl (prolactine)
THY
t4, t3 (metamorphosis)
Showed decrease in metamorphic
mass and possibly PIT dependence
Atrazine had access to the entire pathway, and all studies had an
Endpoint which was metamorphosis. But where are it’s effects?
Why Atrazine?
Henry
HYP
gh (growth hormone)
prl (prolactine)
PIT
“metamorphic barrier”
Used a paedomorphic species
(axolotl) to eliminate thyroid from the
equation.
THY
t4, t3 (metamorphosis)
Atrazine does not have access to the entire pathway. Will there still
be a significant decrease in growth due to atrazine?
Why Competition?
• Environmental stressor
• Interaction with endocrine disruptors
• Density dependent
• Toxicological designs often lack ecologically relevant context
We hypothesized that atrazine, as an endocrine disruptor,
would effect growth, development, and gene expression
in Ambystoma mexicanum (the axolotl salamander)
Experimental Design
1 axolotl
4 axolotls
8 axolotls
Control
1axo/control
4axos/control
8axos/control
1 ppb
1axo/1ppb
4axos/1ppb
8axos/1ppb
5 ppb
1axo/5ppb
4axos/5ppb
8axos/5ppb
This table represents the 9 treatments in one block
1
2
3
4
1 Block
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
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
Results
MANOVA (mass, svl, surv)
Source
Wilks λ
Df
F
P
Atrazine
.837
6,58
.901
.501
Density
.204
6,58 11.722 <.001
Atraz*Dens
.831
12,77 .465
.929
ANOVA (svl)
Source
Atrazine
Density
Atraz*Dens
error
df
2
2
4
31
MS
F
P
.0048 1.04
.366
.0925 19.857 <.001
.0031 .672
.617
.0046
Results
Atrazine x Growth
6000
mg
mass (mg)
5000
4000
3000
2000
1000
0
30
45
60
day
-No significant atrazine effect shown by genomics
75
Results
Density x Growth
9000
8000
mg
mass (mg)
7000
6000
5000
4000
3000
2000
1000
0
30
45
60
day
75
Why Atrazine?
Hayes
Larson, Sih, and Beachy
HYP
PIT
HYP
gh (growth hormone)
prl (prolactine)
Gonads
estrogens
testosterone
Showed decrease testosterone
In males
PIT
gh (growth hormone)
prl (prolactine)
THY
t4, t3 (metamorphosis)
Showed decrease in metamorphic
mass and possibly PIT dependence
Atrazine had access to the entire pathway, and all studies had an
Endpoint which was metamorphosis. But where are it’s effects?
Why Atrazine?
Henry
HYP
PIT
gh (growth hormone)
prl (prolactine)
“metamorphic barrier”
THY
Used a paedomorphic species
(axolotl) to eliminate thyroid from the
equation.
t4, t3 (metamorphosis)
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.
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
Thanks to:
Janel Richter
Ken Cabarle
Claude Ouedraogo
Heather Modrow
Jeremiah Johnson
Karen Pocha-Melby
Biology Department and
The Amphibian Growth Project
Questions?