Virtual Lab
Lizard Evolution Virtual Lab
Experiments in Ecology 2020
Evolution and adaptation
Student Handout
Name: Biswanath Shaw
https://media.hhmi.org/biointeractive/vlabs/lizard2/
LIZARD EVOLUTION VIRTUAL LAB
Module 2: Phylogeny
1. In module 1, you identified which species of lizards were most similar to one another based on
relative limb length and toe pad size. In this module, you determined which lizards are more
similar to one another based on what type of information?
Ans: The DNA extracted from this lizard was used to make a phylogenetic tree based on the similarity of
the DNA sequence. This was used to determine how lizards are similar to one another.
2. Are the species of lizard that are more similar to one another according to body type also more
closely related based on the results obtained in this module? Explain your answer.
Ans: Most of the species of the lizard having same body type are not closely related to one another. They
do not tend to form cluster based on ectomorphs in phylogenetic tree. But if the phylogeny is formed
cluster according to geographical distribution, they tend to form cluster to some extent. This indicate
convergent evolution, the ectomorphs evolved repeatedly and independently on each island to develop
similar ecomorphs.
3. The figures below show two phylogenetic trees similar to the one you constructed in the virtual
lab but with more lizards. The trees below show the evolutionary relationships among species
from four ecomorphs from the four largest Caribbean islands.
Figure 1. Phylogeny of anole lizards on four
of the major Caribbean islands color-coded
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Lizard Evolution Virtual Lab
Student Handout
according to geographical distribution. Light
dotted line, Puerto Rico; small dashed line,
Cuba; large dashed line, Hispaniola; and solid
line, Jamaica.
Figure 2. Phylogeny of anole lizards in the
four major Caribbean islands colored in
according to ecomorph. Light dotted line,
twig; small dashed line, trunk-ground; large
dashed line, trunk-crown; solid line, grassbus
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What conclusion can you draw about the evolution of the Anolis lizards based on these figures?
Answer: When we look at the phylogenetic tree pattern-coded based on islands we see that they seem to
cluster together somewhat: Three of the Jamaican species cluster together as three of the four Peurto
Rican species. Cuban and Hispaniola species also cluster but the pattern is more complicated. If we look at
the phylogenetic tree color-coded based on the ectomorphs we see that there is no clear pattern except
for the two twig species. The phylogenetic tree suggest that the species from the same islands are more
closely related than are species from same ecomorph group. The phylogenetic tree suggest the hypothesis
of convergent evolution.
4. What is convergent evolution? Use evidence from the trees to explain how the Anolis lizards are
an example of this concept.
Answer: Organisms in having different evolutionary history, independently evolving similar traits to adapt
to similar environments or ecological niches is known as convergent evolution.
If we analyze the tree, three of the Jamaican species cluster together as three of the four Peurto Rican
species. Cuban and Hispaniola species also cluster but the pattern is more complicated. If we look at the
phylogenetic tree color-coded based on the ectomorphs we see that there is no clear pattern except for
the two twig species. The phylogenetic tree suggest that the species from the same islands are more
closely related than are species from same ecomorph group. The phylogenetic tree suggest the hypothesis
of convergent evolution.
Module 3: Experimental Data
1. In Dr. Losos’s experiment, why was it important that the experimental islands lacked lizards?
Answer: It was important for Dr. Losos’s experiment to have no lizard is because it allowed each ecomorph
to be isolated and made it easier to study evolution. The data collected won’t be affected by the lizards
originally present there and would help us to compare it with the other islands or originals species.
2. Dr. Losos’s data suggest that after only a few generations, the lizards on the experimental
islands have shorter legs on average than the lizards on the larger island. Explain how the data
you collected either supports or does not support this claim.
Answer:
Mean Relative Hindlimb length
Experimental Island : 0.831 +/- 0.016
Iron Cay( Larger island): 0.871 +/- 0.01
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For some technical reason, the site did not return error bar for Iron Cay group, so I added a error bar using
word.
The data collected support this claim as there is a significant difference relative hindlimb length even after
considering the error bar.
3. Based on what you know about the experimental islands and the lizards that were placed on
these islands, explain how and why the average leg length of the population might change over
time. Include the concept of natural selection in your discussion.
Ans : The average relative length of the hindlimb decreases in the population because in the experimental
island, the longer legs served no advantage while the shorter legs provided with some advantage.
Therefore the lizards having the smaller legs have higher chances of survival, as they would live longer and
reproduce more compared to longer legs, due to natural selection, shorter legs would have increased
number in population
4. If the population from one of the experimental islands were reintroduced on the original island,
do you predict that lizards from the two populations would still mate and reproduce? Justify
your answer with scientific arguments.
Ans : I still think the lizard of experimental island would still be able to mate and reproduce with the
original island populations. In order to develop reproductive barrier it requires lot more time on
evolutionary scale to accumulate changes that makes breeding not possible. The duration of experiment
was no that long that it would be enough to develop reproductive barrier.
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Extension Questions
1. To minimize interspecific competition, organisms often divide the limited available resources in
an area, a concept called “resource partitioning.” As an example of this concept, the figure
below illustrates how different species of warblers utilize different portions of an individual tree.
Figure 3. Different species of North
American warblers live in different
parts of the same trees. The
shaded areas indicate the habitats
each warbler species occupies.
Explain how the different species of anoles on an island demonstrate “resource partitioning”
similar to the warblers in the figure.
Answer: Each of the species of ecomorphs of anoles has developed features to be successful in particular
habitat such as canopy, trunk-crown, trunk, twig, trunk-ground and garden bush, thereby partitioning the
resources among themselves. They live in separate environment just as the warblers have divided the
divided the different sections of tree.
3. Explain how resource partitioning can promote long-term coexistence of competing species,
thus increasing biodiversity.
Ans: Resource partitioning can promote long term coexistence by minimizing competition. There is less
competition because the resources are divided, therefore the more powerful species does not tend to
weaker species extinct by taking away all the resources, promoting coexistence.
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