Section 22.4 (Exam 3)

Question 1

What are the two types of isolation mechanisms?

Answer 1

Prezygotic and postzygotic

Question 2

Explain the function of prezygotic isolation mechanisms.

Answer 2

prevent hybrid offspring (hybridization) from occurring (happens before fertilization occurs)

Question 3

Explain the function of postzygotic isolation mechanisms.

Answer 3

reduce the fitness of hybrid offspring (happens after zygote is formed)

Question 4

What are the 5 types of prezygotic isolation mechanisms?

Answer 4

Mechanical
Temporal
Behavioral
Habitat
Gametic

Question 5

Define mechanical isolation, a type of prezygotic isolation mechanism.

Answer 5

Differences in size and shape of reproductive organs makes mating impossible

Question 6

Define temporal isolation, a type of prezygotic isolation mechanism.

Answer 6

Mating periods do not overlap

Question 7

For allopatric populations, does the overlap of mating periods matter? Why?

Answer 7

No, because even if they did overlap, geographically separated populations cannot mate.

Question 8

Define behavioral isolation, a type of prezygotic isolation mechanism, and provide one example of this.

Answer 8

Individuals fail to recognize or reject potential mating partners because of variations in behavior

One example is a frog mating call having a different frequency.

Question 9

Define habitat isolation, a type of prezygotic isolation mechanism.

Answer 9

When two closely related species evolve habitat preferences that differ from one another, so that they do not encounter each other during overlap of mating periods

Question 10

Define gametic isolation, a type of prezygotic isolation mechanism.

Answer 10

Eggs of one species don’t have appropriate chemical signals for sperm of another species; or sperm can’t attach to the egg.

Important for aquatic species that spawn

Question 11

What are 3 postzygotic isolation mechanisms?

Answer 11

Low hybrid zygote viability

Low hybrid adult viability

Hybrid infertility

Question 12

What is low hybrid zygote viability?

Answer 12

A type of postzygotic isolation mechanism where the zygotes fail to mature or have severe abnormalities

Question 13

What is low hybrid adult viability?

Answer 13

A type of postzygotic isolation mechanism where the offspring have lower survival rates

Question 14

What is hybrid infertility?

Answer 14

A type of postzygotic isolation mechanism where the offspring are infertile

Question 15

Would prezygotic or postzygotic isolation mechanisms be more effective in sympatric species?

Answer 15

Prezygotic isolation mechanisms because they prevent the species from mating altogether

Postzygotic mechanisms would result in a waste of energy and time spent towards developing the offspring that would end up not being viable

Question 16

Would prezygotic or postzygotic isolation mechanisms be more effective in allopatric species?

Answer 16

Postzygotic isolation mechanisms because they prevent the hybrid from being viable if they happen to mate

Prezygotic mechanisms are mostly useless because the species already cannot mate because of a geographic separation

Question 17

What happens if reproductive isolation is incomplete?

Answer 17

A hybrid zone can form where closely related species mate

Question 18

Why is the hybrid zone narrow?

Answer 18

Because postzygotic isolation mechanisms make the hybrid offspring inviable, preventing them from spreading further than the narrow hybrid zone