Lecture12-2008

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Transcript Lecture12-2008

Lecture 12. September 22, 2008.
1. The problems of moving water
A. Grünbaum et al. 2007.
2. Other problems with moving water
What were the goals of the Grünbaum et al. paper?
Arctic charr
Experimental Design
1. cross males and females
2. obtain 13,000 eggs
3. divide eggs into 8 lots
4. choose those that hatch at a close time
5. raise at 4 different water speeds: fast, medium, slow, still,
2 replicates per treatment
6. pull out 4 fish of each of the 8 canals (4 treatments * 2 replicates)
once every 2 days for 100 days
7. measure a bunch of traits
Traits Measured
head length (HL)
head height (HH)
yolk sac height (YSH)
dorsal fin base (DFB)
body height (BH)
anal fin base (AFB)
caudal peduncle height (CPH)
caudal fin height (CFH)
standard length (SL)
total length (TL)
body length (BL) = SL-HL
caudal fin length (CFL) = TL-SL
1. Could they accurately measure their traits?
Yes. Measurement error was
very low (<1%).
2. Did animals differ between the two replicates?
i.e. Did slow canal 1 differ from slow canal 2, etc.?
There were differences between
treatments, but not between
the replicates within treatments.
Table 3 tells us which treatments differed between one another.
In general, what was the pattern with water speed?
Three statistics to understand:
mean
standard deviation


1 N
xi  x

N i 1

2
coefficient of variation = standard deviation / mean
Important Point!
The standard deviation goes up with the mean. If they had just looked
at the standard deviation, they would have concluded that the variability
of the traits went up with time.
The coefficient of variation allows you to look at the variability independent
of the mean.
Does trait variability vary with time and water speed?
medium plasticity?
low plasticity?
medium plasticity?
high plasticity?
medium plasticity?
medium plasticity?
low plasticity?
high plasticity?
high?
low plasticity?
What do these graphs tell us?
Do you agree with the idea that there are two critical periods for development?
Do they define plasticity?
Analysis of Shape
What does this table tell us about shape differences in charr?
What data went into this analysis?
What do these figures tell us about size and shape
in charr?
What are the major “take home” messages from this paper?
On a scale of 1-10 (10 being best), what would you rate this
paper?
Other Challenges Faced by Moving Water
Other Challenges Faced by Moving Water
1. Fertilization - Water speed is infinitely faster than sperm velocity. Water speed
most likely effects sperm traits. Some folks hypothesize that high stream speeds
leads to many, small, short-lived sperm (as opposed to still water).
2. Foraging - Different types of food resources in fast versus still water.
3. Olfaction - Water speed moves chemical cues in a directional fashion.
4. Sound - Streams are nosier than lakes/ponds.
5. Avoiding predators ????
Review Questions
1. Explain the goals/objectives of Grunbaum et al. What was the experimental
design? What data did they collect? How did their data relate to their primary
objectives/questions? What were the null hypotheses (even if they didn’t state
them)?
2. Explain figure 2. What data does this show? What is your interpretation?
3. Explain figure 3. What data does this show? What was the interpretation of
the authors? Did you find this interpretation convincing? What is the
definition of phenotypic plasticity? How would you measure it?
4. Look at table 4. How do the authors interpret PC1, PC2, and PC3? Which
one is more important in explaining overall variation in the measured traits?
Explain what figure 4 C,D, and E show.
5. Explain table 2 and how one calculates measurement error? Was the
measurement error high or low in this study?
6. Graduate students: This paper violates one of my major rules on data
reporting. They rarely report the sample sizes for the means and standard errors
nor do they report the degrees of freedom in the denominator for many of their
tests. Why is this a problem? How big of a problem is this?
Review Questions Cont’d.
7. What do the authors claim is the major result of this paper? Do you believe
it? Do you believe that juvenile Arctic charr get bigger in faster moving water?
8. What is the evidence for the idea that different traits have different critical
windows of time for development? Does this paper provide good evidence
for the authors claims?
9. In general, list several ways that living in moving water differs from living
in still water. What are the implications for reproduction, foraging, sensory
biology, etc.?