In a hypothetical situation, the National Park Service, which administers Grand Canyon National Park in
Arizona, builds a footbridge over the Colorado River at the bottom of the canyon. The footbridge
permits interspersal of two closely related antelope squirrels. Previously, one type of squirrel had been
restricted to the terrain south of the river, and the other type had been restricted to terrain on the north
side of the river. Immediately before and ten years after the bridge’s completion, researchers collected
ten antelope squirrels from both sides of the river, took blood samples, and collected frequencies of
alleles unique to the two types of antelope squirrels (see the following graphs).
38) The data in the previous graphs indicate that
A) a hybrid zone was established after the completion of the bridge.
B) no interspersal of the two types of squirrel occurred after the completion of the bridge.
C) gene flow occurred from one type of squirrel into the gene pool of the other type of squirrel.
D) two-way migration of squirrels occurred across the bridge, but without hybridization.
E) some northern squirrels migrated south, but no southern squirrels migrated north across the bridge.
Scenario Questions
The next few questions refer to the following description.
On the volcanic, equatorial West African island of Sao Tomé, two species of fruit fly exist. Drosophila
yakuba inhabits the island’s lowlands, and is also found on the African mainland, located about 200
miles away. At higher elevations, and only on Sao Tomé, is found the very closely related Drosophila
santomea. The two species can hybridize, though male hybrids are sterile. A hybrid zone exists at
middle elevations, though hybrids there are greatly outnumbered by D. santomea. Studies of the two
species’ nuclear genomes reveal that D. yakuba on the island is more closely related to mainland D.
yakuba than to D. santomea (2n = 4 in both species). Sao Tomé rose from the Atlantic Ocean about 14
million years ago.
39) Which of the following reduces gene flow between the gene pools of the two species on Sao Tomé,
despite the existence of hybrids?
A) hybrid breakdown
B) hybrid inviability
C) hybrid sterility
D) temporal isolation
E) a geographic barrier
40) The observation that island D. yakuba are more closely related to mainland D. yakuba than island D.
yakuba are to D. santomea is best explained by proposing that D. santomea
A) descended from a now-extinct, non-African fruit fly.
B) arrived on the island before D. yakuba.
C) descended from a single colony of D. yakuba, which had been introduced from elsewhere, with no
subsequent colonization events.
D) descended from an original colony of D. yakuba, of which there are no surviving members. The
current island D. yakuba represent a second colonization event from elsewhere.
41) If a speciation event occurred on Sao Tomé, producing D. santomea from a parent colony of D.
yakuba, then which terms apply?
I. macroevolution
II allopatric speciation
III. sympatric speciation
A) I only
B) II only
C) I and II
D) I and III
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42) Using only the information provided in the paragraph, which of the following is the best initial
hypothesis for how D. santomea descended from D. yakuba?
A) geographic isolation
B) autopolyploidy
C) habitat differentiation
D) sexual selection
E) allopolyploidy
43) Which of these evolutionary trees represents the situation described in the previous paragraph (Note:
Yakuba (I) represents the island population, and yakuba (M) represents the mainland population)?
A)
B)
C)
D)
15
44) If the low number of hybrid flies in the hybrid zone, relative to the number of D. santomea flies
there, is due to the fact that hybrids are poorly adapted to conditions in the hybrid zone, and if fewer
hybrid flies are produced with the passage of time, these conditions will most likely lead to
A) fusion.
B) reinforcement.
C) stability.
D) further speciation events.
The next few questions refer to the following description.
On the Bahamian island of Andros, mosquitofish populations live in various, now-isolated, freshwater
ponds that were once united. Currently, some predator-rich ponds have mosquitofish that can swim in
short, fast bursts; other predator-poor ponds have mosquitofish that can swim continuously for a long
time. When placed together in the same body of water, the two kinds of female mosquitofish exhibit
exclusive breeding preferences.
45) Which two of the following have operated to increase divergence between mosquitofish populations
on Andros?
1. improved gene flow
2. bottleneck effect
3. sexual selection
4. founder effect
5. natural selection
A) 1 and 3
B) 2 and 3
C) 2 and 4
D) 3 and 4
E) 3 and 5
46) Which type of reproductive isolation operates to keep the mosquitofish isolated, even when fish
from different ponds are reunited in the same body of water?
A) behavioral isolation
B) habitat isolation
C) temporal isolation
D) mechanical isolation
E) gametic isolation
47) What is the best way to promote fusion between two related populations of mosquitofish, one of
which lives in a predator-rich pond, and the other of which lives in a predator-poor pond?
A) Build a canal linking the two ponds that permits free movement of mosquitofish, but not of predators.
B) Transfer only female mosquitofish from a predator-rich pond to a predator-poor pond.
C) Perform a reciprocal transfer of females between predator-rich and predator-poor ponds.
D) Remove predators from a predator-rich pond and transfer them to a predator-poor pond.
48) If one builds a canal linking a predator-rich pond to a predator-poor pond, then what type(s) of
selection should subsequently be most expected among the mosquitofish in the original predator-rich
pond, and what type(s) should be most expected among the mosquitofish in the formerly predator-poor
pond?
A) stabilizing selection; directional selection
B) stabilizing selection; stabilizing selection
C) less-intense directional selection; more-intense directional selection
D) less-intense disruptive selection; more-intense disruptive selection
49) The predatory fish rely on visual cues and speed to capture mosquitofish. Mosquitofish rely on
speed and visual cues to avoid the predatory fish. Which adaptation(s) might help the predators survive
in ponds that are home to faster mosquitofish?
1. directional selection for increased speed
2. stabilizing selection for speed that matches that of the mosquitofish
3. change in hunting behavior that replaces reliance on visual cues with reliance on tactile cues, which
can be used to hunt at night
4. change in hunting behavior that eliminates speed in favor of better camouflage, which permits an
ambush strategy
A) 1 only
B) 2 only
C) either 1 or 3
D) either 2 or 3
E) 1, 3, or 4
The next few questions refer to the following description.
In the ocean, on either side of the Isthmus of Panama, are 30 species of snapping shrimp; some are
shallow-water species, others are adapted to deep water. There are 15 species on the Pacific side and 15
different species on the Atlantic side. The Isthmus of Panama started rising about 10 million years ago.
The oceans were completely separated by the isthmus about 3 million years ago.
50) Why should deepwater shrimp on different sides of the isthmus have diverged from each other
earlier than shallow-water shrimp?
A) They have been geographically isolated from each other for a longer time.
B) Cold temperatures, associated with deep water, have accelerated the mutation rate, resulting in faster
divergence in deepwater shrimp.
C) The rise of the land bridge was accompanied by much volcanic activity. Volcanic ash contains heavy
metals, which are known mutagens. Ash fall caused high levels of heavy metals in the ocean sediments
underlying the deep water, resulting in accelerated mutation rates and faster divergence in deepwater
shrimp.
D) Fresh water entering the ocean from the canal is both less dense and cloudier than seawater. The
cloudy fresh water interferes with the ability of shallow-water shrimp to locate mating partners, which
reduces the frequency of mating, thereby slowing the introduction of genetic variation.
18
The next few questions refer to the following description.
In the ocean, on either side of the Isthmus of Panama, are 30 species of snapping shrimp; some are
shallow-water species, others are adapted to deep water. There are 15 species on the Pacific side and 15
different species on the Atlantic side. The Isthmus of Panama started rising about 10 million years ago.
In the following figure, the isthmus separates the Pacific Ocean on the left (side A) from the Atlantic
Ocean on the right (side B). The seawater on either side of the isthmus is separated into five depth
habitats (1—5), with 1 being the shallowest.
51) In which habitat should one find snapping shrimp most closely related to shrimp that live in habitat
A4?
A) A3
B) A5
C) B4
D) either A3 or A5
E) any species from any one of the side A habitats
52) Which of these habitats is likely to harbor the youngest species?
A) A5
B) B4
C) A3
D) B2
E) A1
53) Which habitats should harbor snapping shrimp species with the greatest degree of genetic
divergence from each other?
A) A1 and A5
B) A1 and B5
C) B5 and B1
D) A5 and B5
E) Both A1/A5 and B1/B5 should have the greatest, but equal amounts of, genetic divergence.
54) Which factor is most important for explaining why there are equal numbers of snapping shrimp
species on either side of the isthmus?
A) the relative shortness of time they have been separated
B) the depth of the ocean
C) the number of actual depth habitats between the surface and the sea floor
D) the elevation of the isthmus above sea level
E) the depth of the canal
55) The Panama Canal was completed in 1914, and its depth is about 50 feet. After 1914, snapping
shrimp species from which habitats should be most likely to form hybrids as the result of the canal?
A) A5 and B5
B) A3 and B3
C) A1 and B1
D) either A1 and A2, or B1 and B2
E) A1—A3 and B1—B3 have equal likelihoods of harboring snapping shrimp species that can
hybridize.
56) There are currently two, large, permanent bridges that span the Panama Canal. The bridges are about
8 miles apart. If snapping shrimp avoid swimming at night and avoid swimming under shadows, then
what do these bridges represent for the snapping shrimp?
A) sources of refuge
B) geographic barriers
C) sources of a hybrid zone between the two bridges
D) sources for increased gene flow
End-of-Chapter Questions
The following questions are from the end-of–chapter “Test Your Understanding” section in Chapter 24
of the textbook.
57) The largest unit within which gene flow can readily occur is a
A) population.
B) species.
C) genus.
D) hybrid.
E) phylum.
58) Males of different species of the fruit fly Drosophila that live in the same parts of the Hawaiian
Islands have different elaborate courtship rituals. These rituals involve fighting other males and making
stylized movements that attract females. What type of reproductive isolation does this represent?
A) habitat isolation
B) temporal isolation
C) behavioral isolation
D) gametic isolation
E) postzygotic barriers
59) According to the punctuated equilibria model,
A) natural selection is unimportant as a mechanism of evolution.
B) given enough time, most existing species will branch gradually into new species.
C) most new species accumulate their unique features relatively rapidly as they come into existence,
then change little for the rest of their duration as a species.
D) most evolution occurs in sympatric populations.
E) speciation is usually due to a single mutation.
60) Bird guides once listed the myrtle warbler and Audubon’s warbler as distinct species. Recently, these
birds have been classified as eastern and western forms of a single species, the yellow-rumped warbler.
Which of the following pieces of evidence, if true, would be cause for this reclassification?
A) The two forms interbreed often in nature, and their offspring have good survival and reproduction.
B) The two forms live in similar habitats.
C) The two forms have many genes in common.
D) The two forms have similar food requirements.
E) The two forms are very similar in coloration.
61) Which of the following factors would not contribute to allopatric speciation?
A) A population becomes geographically isolated from the parent population.
B) The separated population is small, and genetic drift occurs.
C) The isolated population is exposed to different selection pressures than the ancestral population.
D) Different mutations begin to distinguish the gene pools of the separated populations.
E) Gene flow between the two populations is extensive.
62) Plant species A has a diploid number of 12. Plant species B has a diploid number of 16. A new
species, C, arises as an allopolyploid from A and B. The diploid number for species C would probably
be
A) 12.
B) 14.
C) 16.
D) 28.
E) 56.
63) Suppose that a group of male pied flycatchers migrated from a region where there were no collared
flycatchers to a region where both species were present. Assuming events like this are very rare, which
of the following scenarios is least likely?
A) The frequency of hybrid offspring would increase.
B) Migrant pied males would produce fewer offspring than would resident pied males.
C) Pied females would rarely mate with collared males.
D) Migrant males would mate with collared females more often than with pied females.
E) The frequency of hybrid offspring would decrease.