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.