1.8.3 Prezygotic Reproductive Isolation

Question 1

two categories of reproductive isolation

Answer 1

• prezygotic isolation and postzygotic isolation

Question 2

prezygotic isolation

Answer 2

• barriers to reproductive events that take place before fertilization
• mechanisms include isolation by habitat, behavioral isolation, temporal isolation, mechanical isolation, and gametic isolation.

Question 3

postzygotic isolation

Answer 3

• barriers to reproduction that occur after fertilization has taken place.

Question 4

isolation by habitat

Answer 4

• Organisms that live in different habitats are much less likely to have contact with each other and mate.
• Example: If some flies were attracted to apples and others attracted to pears, they would be separated by their habitats and less likely to mate.

Question 5

behavioral isolation

Answer 5

• Courtship behaviors prior to mating can be species specific. If a courtship behavior is neither recognized nor desirable to an organism, it will not mate.
• For example, if a male presents the wrong
  type of food to a female, she might not mate.

Question 6

temporal isolation

Answer 6

• Organisms that mate at different times or have different breeding seasons will not be able to mate together.
• For example, the eastern and western spotted skunks do not interbreed because they have different mating seasons.

Question 7

mechanical isolation

Answer 7

• If the reproductive organs do not fit between different populations, individuals will be unable to mate.
• For example, male spiders have organs called
  pedipalps that deposit the sperm into the female. If the pedipalps don’t fit the female, the spiders will be unable to mate together.

Question 8

gametic isolation

Answer 8

• There must be biochemical recognition between the sperm and the egg. If the egg does not recognize certain chemical markers on the sperm, or if the sperm cannot penetrate the egg, fertilization will not occur.

Question 9

Which of the following is not a prezygotic barrier to reproduction?

Answer 9

• The hybrid of two different species of the genus Anopheles is unable to reproduce successfully.

Question 10

Following are four descriptions of prezygotic reproductive isolation. Place them in order of behavioral isolation, temporal isolation, mechanical isolation, and gametic isolation.
A. A male diamondback rattlesnake cannot mate with a female New Mexico ridge nose rattlesnake because the male’s hemipenes (sex organs) do not fit properly in the female.
B. A male bower bird cannot mate with an emu for many reasons, but one is that the emu does not recognize the male bower bird’s offering of a shelter he built himself.
C. A male from one fruit fly species mates with a female from another species, but his sperm die before they fertilize the egg.
D. The males of one turtle population are ready to mate in June, but the females of a second turtle population ended their mating season in May.

Answer 10

• B, D, A, C

Question 11

A species of fly only mates within a purple flower. One day, a fly is born with a mutation that makes a yellow flower more attractive, and he avoids the purple flower entirely. Which of the following scenarios describes (1) the necessary events for that mutation to persist in the population and (2) a possible outcome if the mutation does persist?

Answer 11

• Another fly must be born with a mutation that gives it a preference for yellow flowers. The fly must be female and mate with the original, yellow-flower-loving male. They will produce offspring that also are attracted to yellow flowers, and thus, the mutation will persist. Eventually, two groups of flies will arise: flies that mate only in purple flowers and flies that mate only in yellow flowers. Because the two populations are isolated based on their behavior, speciation occurs.

Question 12

An example of _________ takes place when two individuals of different populations mate, but their gametes cannot fuse to form a zygote.

Answer 12

• gametic isolation

Question 13

Speciation takes place relatively quickly within lineages in which species have complex behavior. The best explanation of this is that

Answer 13

• individuals within these species are much more discriminating in choosing potential mates

Question 14

Which of the following is not an example of a prezygotic isolation mechanism?

Answer 14

• sterility of hybrids