Lecture 12. September 22, 2008.

1. The problems of moving waterA. Grünbaum et al. 2007.

2. Other problems with moving water

What were the goals of the Grünbaum et al. paper?

Arctic charr

1. cross males and females2. obtain 13,000 eggs3. divide eggs into 8 lots4. choose those that hatch at a close time5. 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

Experimental Design

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-HLcaudal 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 betweentreatments, but not betweenthe 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

coefficient of variation = standard deviation / mean

21

1 N

ii

x xN

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 variabilityof the traits went up with time.

The coefficient of variation allows you to look at the variability independentof the mean.

Does trait variability vary with time and water speed?

low plasticity?

low plasticity?low plasticity?

medium plasticity?

medium plasticity?

medium plasticity?

medium plasticity?

high?

high plasticity? high 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 shapein charr?

What are the major “take home” messages from this paper?

On a scale of 1-10 (10 being best), what would you rate thispaper?

Other Challenges Faced by Moving Water

Other Challenges Faced by Moving Water

1. Fertilization - Water speed is infinitely faster than sperm velocity. Water speedmost 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 experimentaldesign? What data did they collect? How did their data relate to their primaryobjectives/questions? What were the null hypotheses (even if they didn’t statethem)?

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 ofthe 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 errorsnor 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 believeit? 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 criticalwindows 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.?