AP Biology : 7.10 Speciation – Exam Style questions with Answer- MCQ

Question

Some species of birds have unique bird songs that only attract members of the same species. This is an example of which type of reproductive
isolation?
(A) behavioral
(B) gametic
(C) habitat
(D) mechanical

▶️Answer/Explanation

Ans:

(A) Bird songs are an example of behavioral isolation. Choice (B) is
incorrect because gametic isolation occurs when gametes are
incompatible and cannot form a zygote. Habitat isolation involves
separation by area, so choice (C) is incorrect. Mechanical isolation
occurs when the genitalia of the male and female cannot successfully
copulate, so choice (D) is incorrect.

Question

Orchids that belong to the genus Dendrobium will flower in response to certain weather stimuli. One species of Dendrobium flowers on the 8th day and closes on the 9th day after the weather stimuli, while another species of Dendrobium flowers on the 10th day and closes on the 11th
day after the weather stimuli. This is an example of which type of reproductive isolation?
(A) habitat
(B) mechanical
(C) temporal
(D) hybrid breakdown

▶️Answer/Explanation

Ans:

(C) Temporal isolation is separation by time. Since the two species
flower and are ready for pollination at different times, this is an
example of temporal isolation. Habitat isolation is separation by area,
so choice (A) is incorrect. Choice (B) is incorrect because mechanical
isolation occurs when the male and female genitalia are incompatible.
Hybrid breakdown occurs when two species can produce a viable and
fertile offspring but each successive generation of the hybrid becomes
weaker and weaker, so choice (D) is incorrect.

Question

Which of the following is an example of mechanical reproductive isolation?
(A) The sea urchin species Strongylocentrotus purpuratus and Strongylocentrotus franciscanus both live in the same marine habitat and release their gametes simultaneously into the surrounding water. However, the gametes cannot form a zygote.
(B) In some snail species, the direction of the coil of the shell is controlled by a single gene. Snails with left-coiling shells cannot mate with snails with right-coiling shells because their copulating organs do not align.
(C) The fruit fly species Drosophila persimilis breeds in the early morning, and the fruit fly species Drosophila pseudoobscura breeds in the late afternoon.
(D) The bullfrog species Rana draytonii and Rana catesbeiana can mate and produce a zygote, but the zygote is not viable.

▶️Answer/Explanation

Ans:

(B) Since their copulating organs do not align, these snails cannot
exchange gametes, so this is an example of mechanical isolation.
Choice (A) is an example of gametic isolation. Choice (C) is an
example of temporal isolation. Choice (D) is an example of reduced
hybrid viability.

Question

Tigers (Panthera tigris) and leopards (Panthera pardus) can mate and produce a zygote. The zygote will undergo cell division a few times,
but this fails to result in the production of a viable embryo. This is an example of which type of reproductive isolation?
(A) gametic
(B) reduced hybrid viability
(C) reduced hybrid fertility
(D) hybrid breakdown

▶️Answer/Explanation

Ans:

(B) Since tigers and leopards can mate and produce a zygote, but doing
so does not result in any viable offspring, this is an example of reduced
hybrid viability. It is not gametic isolation since their gametes can form
a zygote, so choice (A) is incorrect. There is no infertile adult hybrid in this scenario, so choice (C) is also incorrect. No viable hybrid was
produced, so there is no chance of hybrid breakdown, making choice
(D) incorrect.

Question

Diagram of the greenish warbler, Phylloscopus trochiloides. Each circle represents a species. A is believed to be the ancestral species, with radiation moving out (B → D → F → G and C → E → H).

Which pairs of species are most likely to be not able to breed?
(A) A and H
(B) B and C
(C) D and E
(D) G and H

▶️Answer/Explanation

Ans: D

A ring species, in which two reproductively isolated taxa are
connected by a chain of interbreeding populations, provides a rare
opportunity to use spatial variation to reconstruct the history of
divergence. If A is the ancestral species, then A and B, and B and C are
more closely related. If there is gene flow between A and B, and A and C,
then there must be gene flow between B and C. A and H probably won’t
interbreed if “given the chance,” but G and H are the least likely since they
are the two most recent divergences from two lineages that separate the
longest time ago.

Question

Diagram of the greenish warbler, Phylloscopus trochiloides. Each circle represents a species. A is believed to be the ancestral species, with radiation moving out (B → D → F → G and C → E → H).

Of the following true statements, which is the weakest piece of evidence to support the proposed radiation?
(A) Plumage patterns and wing bar patterns change gradually from species A → G and A → H. Groups G and H differ most in their feather appearance.
(B) Species E and D have the same number of DNA sequence differences (compared to species A) in a specific, homologous region of DNA.
(C) Species A has the simplest song. Songs of the bird groups on each side of species A increase in complexity northward. Groups G and H have the most complex songs.
(D) Groups F and G can interbreed, groups C and E can interbreed, but groups G and H cannot interbreed.

▶️Answer/Explanation

Ans: B

Answer choices A, C, and D are all true and were part of the
construction of the proposed ring structure. The differences among groups
in the ring gradually increases as the distance increases. For example,
the difference in plumage between groups A and B are less dramatic than
the differences between groups A and G. Choice B may be true, but it does
not support the ring structure. It suggests that species E and D diverged
from the ancestor A at about the same time. If E and D had the same number of differences between each of the species and A, it would support E and D as being more closely related.
See the box after answer 6 for a strategy for answering questions asked in
the negative and using the process of elimination.

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