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Artificial Selection
Refer to the graphs below. The data is from a study during which the investigators used artificial
selection, selecting fish for breeding on the basis of brain size to create two distinctly different F 2
generations.1 Figure 1 displays the change in brain size as a result of artificial selection, and the
average brain size of four populations created for the purpose of the study: smaller-brained and
larger-brained females, and smaller-brained and larger-brained males. The researchers developed a
“learning test” to measure the cognitive ability of the fish and compared females of different brain
sizes and males of different brain sizes. (Error bars indicate SEM.)
a. The scientists concluded that there is a correlation between brain size and cognitive ability for
female guppies but that the correlation does not hold true for male guppies. Describe evidence
from Figure 2 that supports the scientists’ conclusion.
b. The scientists also compared the mean number of offspring produced by each category of
female at first reproduction. The data are shown in Figure 3. The scientists used artificial
selection in the laboratory to increase brain size in females. Do you predict natural selection
will favor large-brained females? Provide evidence to support your prediction.
Energy Dynamics
Researchers carried out numerous experiments designed to study decomposition rates under a
variety of conditions.2 The experiments were designed to model the decomposition that occurs in an
Australian stream. Three different leaf-shredding detritivore species were taken from the stream for
use in the study, leaves from three native riparian tree species were collected for use as plant litter,
and the researchers carried out experiments in model stream habitats at two different temperatures
(typical stream temperature and 5 °C warmer). In total, almost 200 experiments were performed by
the researchers.
Kotrschal et al., Artificial Selection on Relative Brain Size in the Guppy Reveals Costs and Benefits of Evolving a Larger Brain, Current
Biology (2013), http://dx.doi.org/10.1016/j.cub.2012.11.058.
2 Boyero, L.; Bradley, J.C.; Bastian, M; Pearson, R.G. Biotic vs. Abiotic Control of Decomposition: A Comparison of the Effects of Simulated
Extinctions and Changes in Temperature. PLoS ONE (Impact Factor: 3.73). 01/2014; 9(1):e87426. DOI:10.1371/journal.pone.0087426
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0087426 (accessed July 3, 2014).
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DATA ANALYSIS PRACTICE / STUDENT HANDOUT
The following diagram illustrates the results of these experiments. The bars show the mean
detritivore-mediated decomposition rates measured as a proportion of leaf weight loss per
detritivore (prop. LWL). Detritivores were present in all trials; the species identity or richness of
detritivores was manipulated for some trials, as was the species identity or richness of plant
litter. Each manipulation of detritivores or plant litter species was tested at two temperatures.
Researchers performed a variety of statistical analyses to the data and the resulting probability
values p are provided below each graph.
Table 1: Statistical analysis of decomposition rates under different conditions of detritivore, leaf litter, and
temperature
Statistical Comparisons
Species Identity: compared decomposition
rate by Ak, Lv, and Tg and
compared rates of decomposition of
Ab, Cl, and Eb
Species Richness: compared the polyculture
decomposition rates to the single-species decomposition
rates
Detritivores
p < 0.001
p = 0.79
Plant litter
p < 0.001
p = 0.83
Compared decomposition rates in low temperature and high temperature stream water
Temperature
p < 0.001
a. Identify two scientific questions that the researchers were likely investigating with these
experiments.
b. For one of the scientific questions you describe, propose an experimental design for the
experiment used to test the question. Be sure to make clear the independent and dependent
variables, as well as the constant variables for the proposed experimental design.
c. What can be concluded from the provided probability values?
d. For either detritivores or plant litter, identify a characteristic of the organism or leaves that
may contribute to faster or slower decomposition.
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DATA ANALYSIS PRACTICE / STUDENT HANDOUT
Transpiration
The table below summarizes data from a study of various species of Eucalyptus trees. During
24-hour time periods, a portable photosynthesis system was used to measure net carbon dioxide
exchange for a sample of leaves from three or four trees of each species. Photosynthetic rate and
stomatal conductance were calculated from data collected with the portable system. Stomatal
conductance relates to the proportion of open stomata; the greater the number of open stomata, the
greater the stomatal conductance.3
Table 3: Effect of time of day on photosynthetic rate and stomatal conductance in Eucalyptus trees
Species
Time of Day and Photosynthetic Rate
(µmol CO2
E. argophloia
E. dunnii
E. sideroxylon
/m2)/s)
Stomatal Conductance
(mol CO2 /m2)/s)
06:00
–1.5
0.02
09:00
1
0.04
11:00
7.5
0.10
13:00
7
0.08
16:00
4
0.02
19:00
2
0.01
06:00
–1
0.01
09:00
3
0.03
11:00
9.5
0.12
13:00
5
0.05
16:00
3
0.02
19:00
1
0.01
06:00
–4
0.02
09:00
2.5
0.03
11:00
13
0.28
13:00
12.5
0.28
16:00
8
0.11
19:00
4.5
0.02
a. Describe the trend in stomata opening and closing over the course of 24 hours. Describe the
environmental factors that are likely to be the cause of this trend.
b. Create an appropriately labeled scatter plot graph of Photosynthetic rate versus Stomatal
conductance. Use a different symbol for each species.
c. Describe the relationship between photosynthetic rate and the proportion of open stomata in
leaves.
Lewis, J.; Phillips, N.; Logan, B.; Hricko, C.; Tissue, D. Leaf photosynthesis, respiration and stomatal conductance in six Eucalyptus species
native to mesic and xeric environments growing in a common garden. Tree Physiol (2011) 31 (9): 997-1006. doi: 10.1093/treephys/tpr 087
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DATA ANALYSIS PRACTICE / STUDENT HANDOUT
Plant Pigments and Photosynthesis
In the Baltic Sea, two similar species of photosynthetic picocyanobacteria were found to occupy water
at a similar depth. One species, BS4, is blue-green in color and the other species, BS5, is red. Both
species contain chlorophyll a but differ in the presence of certain accessory pigments: phycocyanin is
found only in BS4 and phycoerythrin is found only in BS5. The absorbance spectra for the pigments
in these species are shown below. Also shown are the results of experiments in which the species
were grown together under different light conditions. 4
a. Explain why the picocyanobacterium BS5 is red in color.
b. Describe evidence from the absorbance spectra that both of the species contain chlorophyll a.
c. Describe the results of growing BS4 and BS5 together in green light and provide a biological
explanation for the results.
d. Describe the results of growing BS4 and BS5 together in white light and provide a biological
explanation for the results.
e. If paper chromatography was performed using pigments extracted from BS5, what color or
colors would you expect to see on the paper after chromatography is complete? Explain the
reasoning for your choice(s).
Stomp, M. et al. Adaptive divergence in pigment composition promotes phytoplankton biodiversity. Nature (Impact Factor: 38.6). 12/2004;
432(7013):104–7. DOI: 10.1038/nature03044
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