Unformatted text preview: The Origin of Species:
Lizards in an Evolutionary Tree
NAME_______________________ Film Guide
DATE_________________ This handout supplements the short film The Origin of Species: Lizards in an Evolutionary Tree.
1. Puerto Rico, Cuba, Jamaica, and Hispaniola have species of anole lizards with distinct body types, including
the grass lizards, which have long tails; the canopy lizards, which have large toe pads; and the twig lizards,
which have short legs. Anole species with each of these three body types exist on each of the four islands.
The phylogenetic trees in the figure below illustrate two hypotheses for how these types of lizards may have
evolved. a. Select the pair of statements in the table below that accurately describe the phylogenetic trees in the
figure above: _________
B C D Tree on the Left Side of the Figure
The twig lizard on Puerto Rico evolved first
and is the ancestor of all the other lizards.
Body types evolved repeatedly and
independently on each island.
Different body types evolved only once, and
then populations of individuals with those
body types ended up on different islands.
Puerto Rico is the origin of all three lizard
body types. The Origin of Species
Tree on the Right Side of the Figure
The twig lizard evolved first on all of the islands, and then
the canopy and grass lizards evolved from the twig lizard.
Different body types evolved once, and then populations
of individuals with those body types ended up on different
There are two ancestors to all the lizards, the twig lizard
and the canopy lizard.
Each body type evolved repeatedly and independently on
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Page 1 of 5 The Origin of Species: Lizards in an Evolutionary Tree Film Guide
Student Handout b. Select which tree in the figure illustrates the most likely hypothesis for how the different species of anole lizards evolved on the Caribbean islands according to the film: X
the tree on the left
_____ the tree on the right c. Using evidence presented in the film, explain the reasoning behind your answer in the question above
(Part b). Jonathan Losos and his colleagues sequenced the DNA of anoles from each island. The DNA
revealed that the lizards on each island tend to be more closely related to each other than to
similar-looking lizards elsewhere. This means that generally the same types of lizards evolved
independently on each island
2. Over many generations, natural selection favors those traits that enable populations to live successfully in a
particular habitat. A scientist discovered two species of anole lizards that live in different habitats and
display the characteristics listed in the table below. (The scientists based these observations on a sample of
20 lizards from each species.)
Tail length Observations of Two Species of Anoles
High trunks and branches Lower trunk and ground
Long a. Describe two differences between the two species of anoles.
One difference is that species A lives high up on tree trunks and branches, whereas species B lives
lower down on trunks and on the ground. A second difference is that the limbs of species A are relatively short and
those of species B are long. The sizes of the two lizard species bodies and toe pads are also different b. Formulate two hypotheses to explain why each of these differences may have evolved. One hypothesis is that by living higher up on the trunks and in the branches of trees, species A
avoids competition for resources with species. Second hypothesis is that longer limbs are an
adaptation for living lower in the trees and on the ground because individuals with longer limbs
can run faster and escape predators on the ground. c. Describe an experiment that would test one of your hypotheses stated above. Make two lizards from speicies A and B race and tack their speed. Lizards with longer legs will
run faster. The Origin of Species
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Page 2 of 5 The Origin of Species: Lizards in an Evolutionary Tree Film Guide
Student Handout C
3. Two organisms are considered to belong to different species if they __________
a. have differences in appearance, such as different color or leg length.
b. live in different geographical areas, such as on different islands.
c. do not mate or produce fertile offspring.
d. eat entirely different types of foods. 4. In the film, you saw Jonathan Losos place a male and female trunk-ground anole on an island that did not
have any trees but had short grass and shrubs. Losos and colleagues visited the island the following year.
What had happened? _______
a. The two anoles died because there were no trees for them to live in.
b. The two anoles reproduced and their offspring adapted to living in bushes.
c. The legs of the two anoles got shorter and their offspring inherited shorter legs.
d. The two anoles reproduced and there were no significant differences in traits from one generation to
5. Which statement best explains why islands can be used as natural laboratories? ________
a. The climate among islands varies from very wet to very dry.
b. Islands are smaller in size than the mainland, so in that sense they are like a laboratory.
c. The islands have similar habitats, but they differ from the mainland habitat.
d. There are many small islands, meaning researchers can repeat their observations and experiments on
several similar islands. 6. Describe the similarities and differences between the terms microevolution and macroevolution.
Microevolution and macroevolution are similar in that both involve genetic changes in populations over time.
Microevolution and macroevolution are different in that microevolution involves changes within populations that do
not prevent breeding between one group and another. With macroevolution, changes within populations accumulate
until individuals from one group no longer recognize individuals from another group as potential mates or they are
no longer able to produce fertile offspring 7. List two lines of evidence that Jonathan Losos has gathered through observation and experimentation that
support the theory of natural selection developed by Charles Darwin. - Losos observed the same distribution of similar-looking lizardson each island.
- Each island has lizards with the same basic body types: slender grass-bush anoles with long
tails, longlegged stocky trunk-ground anoles, small short-legged twig anoles, and canopy anoles
with large toe pads. The Origin of Species
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Page 3 of 5 Film Guide
Student Handout The Origin of Species: Lizards in an Evolutionary Tree Use the following information and figure to answer Questions 8-9.
In 2003, Jonathan Losos and his research team experimentally introduced curly-tailed lizards (Leiocephalus
carinatus) to islands populated by trunk-ground anoles that live primarily on the ground and have relatively long
legs (Losos, J. B., T. W. Schoener, and D. A. Spiller. 2004. Predator-induced behaviour shifts and natural selection
in field-experimental lizard populations. Nature 432: 505-508). The scientists wanted to know how the presence
of the curly-tailed lizards, which are anole predators, would affect the habitat in which the anoles lived.
In one experiment, Losos and colleagues
measured the “perch height” (or how high
off the ground a lizard was perched) for 24
individual anoles. They then placed either a
curly-tailed lizard (experimental population)
or an inanimate object of the same size
(control population) in front of individual
trunk-ground anoles and measured the
perch height 10 minutes later. They then
calculated the average change in the anole’s
perch height in the experimental and control
populations. The results of this experiment
are summarized in Figure 1.
Figure 1. Mean change in perch height (±1 standard error) 10
minutes after introduction of either a large predatory lizard
(experimental) or an inanimate object of the same size (control).
(Image reproduced with permission from Losos, J. B., T. W.
Schoener, and D. A. Spiller. 2004. Nature 432: 505-508.) 8. Based on the information above, what research question did the scientists ask that led to this experiment? How do ground anoles evolve in the presence of a potential predator? 9. Using the information in Figure 1, describe the results of the experiment. In the presence of a live curly-tailed lizard, the ground anoles started living higher off the ground.
The data show that they shifted their perch height by an average of 0.6 meters. The average
perch height did not change for the anoles that were exposed to an inanimate object the same
size as a curly-tailed lizard The Origin of Species
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Page 4 of 5 The Origin of Species: Lizards in an Evolutionary Tree Film Guide
Student Handout Use the following information and figure to answer Questions 10-12.
In another experiment, the scientists left the curly-tailed lizards on the islands for several weeks. They counted
the number of anoles living on the ground at the beginning of the experiment in May and then again in July and
November. The figure below shows the percentage of anoles living on the ground on islands with curly-tailed
lizards (experimental population) and without curly-tailed lizards (control population). Figure 2. Differences in proportions
of anoles observed on the ground in
experimental and control
populations. Values are mean and ±1
standard error of the mean for all 12
islands. Only four islands were
surveyed in July. (Image reproduced
with permission from Losos, J. B., T.
W. Schoener, and D. A. Spiller. 2004.
Nature 432: 505-508.) 10. Based on the information above, what research question did the scientists ask that led to this experiment? How will the presence of a predator affect the habitat occupied by ground anoles over several
weeks? 11. Using the information in Figure 2, describe the results of the experiment. After several weeks, the percentage of ground anoles in the experimental population that were
living on the ground had dropped from 0.5 to almost 0.1, whereas the percentage of ground
anoles in the control population that were living on the ground had dropped to 0.35. 12. Provide a scientific explanation for the results of the two experiments summarized in Figures 1 and 2. (Hint:
Imagine that you are one of the anoles in each experiment.) The experiments basically show that in the presence of a predator, the anoles move higher up
into the trees, and when the predator is on the island, they are less likely to be found on the
ground. They aren't up in the trees all the time because the predator isn't always right in front of
13. If the curly-tailed lizards were left on the islands for several years, predict how the bodies of the trunkground anoles might change after many generations of living in the presence of curly-tailed lizards. The anoles living in the shrubs will likely have shorter limbs after several generations. The Origin of Species
Revised March 2018
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