24.1 – 1
Two bird species in a forest are not
known to interbreed. One species
feeds and mates in the treetops and the
other on the ground. But in captivity,
the two species can interbreed and
produce viable, fertile offspring. What
type of reproductive barrier most likely
keeps these species separate?
Explain.
24.1 – 1
Since the birds are known to
breed successfully in captivity,
the reproductive barrier in nature
must be prezygotic. Given the
species differences in habitat
preference, the reproductive
barrier is most likely to be
habitat isolation.
24.1 – 2
a. Which species concept can be
used for both sexual and asexual
species?
b. Which can only be applied to
sexual species?
c. Which would be most useful for
identifying species in the field?
24.1 – 2
a. All species concepts except
the biological species concept can
be applied to both asexually and
sexually reproducing species
because they define species
based on characteristics other
than the ability to reproduce.
24.1 – 2
b. The biological species concept
can be applied only to extant
sexual species.
24.1 – 2
c. The easiest species concept to
apply in the field would be the
morphological species concept
because it is based only on the
appearance of the organism.
Additional information about its
ecological habits, evolutionary
history, and reproduction are not
required.
24.2 – 1
Explain why allopatric speciation
would be less likely to occur on an
island close to a mainland than on a
more isolated island of the same
size.
24.2 – 1
Continual gene flow between
mainland populations and those on
a nearby island reduces the
chance that enough genetic
divergence will take pace for
allopatric speciation to occur.
24.2 – 2
Normal watermelon plants are diploid (2n = 22),
but breeders have produced tetraploid (4n = 44)
watermelons.
If tetraploid plants are hybridized with their diploid
relatives, they produce triploid (3n = 33) seeds
.
These offspring can produce triploid seedless
watermelons and can be further propagated by
cuttings
.
Are the diploid and tetraploid watermelon plants
different species? Explain.
24.2 – 2
The diploid and tetraploid
watermelons are separate species.
Their hybrids are triploid and as a
result are sterile because of
problems carrying out meiosis.
24.2 – 3
In the fossil record, transitional
fossils linking newer species to
older ones are relatively rare.
Suggest an explanation for this
observation.
24.2 – 3
According to the model of punctuated
equilibrium, in most cases the time during
which speciation (that is, the distinguishing
evolutionary changes) occurs is relatively short
compared with the overall duration of the
species’ existence. Thus, on the vast geologic
time scale of the fossil record, the transition
of one species to another seems abrupt, and
instances of gradual change in the fossil are
rare. Furthermore, some of the changes that
transitional species underwent may not be
apparent in fossils.
24.3 – 1
How can the Darwinian concept of
descent with modification explain
the evolution of such complex
structures as the vertebrate eye or
heart?
24.3 – 1
Such complex structures do not
evolve all at once, but in
increments, with natural selection
selecting for adaptive variants of
the earlier versions.
24.3 – 2
Explain why the concept of
exaptation does not mean that a
structure evolves in anticipation of
some future environmental change.
24.3 – 2
Although an exaptation is coopted for new or additional
functions in a new environment, it
existed in the first place because
it worked as an adaptation to the
original environment.
24.3 – 3
How can heterochrony cause the
evolution of different body forms?
24.3 – 3
The timing of different
developmental pathways in
organisms can change in different
ways (heterochrony). This can
result in differential growth
patterns, such as those producing
different patterns of webbing in
salamander feet.