Chapter 22, Problem 1U

Prezygotic isolating mechanisms include all of the following except

a. hybrid sterility.

b. courtship rituals.

c. habitat separation.

d. seasonal reproduction

Summary Introduction

Introduction:

The reproductive isolation is achieved through the reproductive barriers which are the evolutionary mechanism or behaviors that prevent organism of a different species from breeding and leads to the prevention of exchange of genetic material. There are two types of reproductive barriers: Prezygotic barrier prevents the fertilization between species and postzygotic barrier prevents the maturation of hybrid zygote formed by the mating of two different species. Prezygotic barrier involves habitat, mechanical, gametic, behavioral, and temporal isolation. Postzygotic barriers involve reduced viability of the hybrid formed, reduced fertility of the hybrid and the breakdown of the hybrid that result in the sterile generations.

Answer to Problem 1U

Correct answer:

Hybrid sterility is the postzygotic barrier in which the produced hybrid formed due to the mating of two different species either does not develop properly (are sterile) or the adults do not survive for long. Therefore option a. is the correct answer.

Explanation of Solution

Reason for the correct statement:

The isolating mechanisms that prevent the formation of a zygote are known as the prezygotic isolation mechanism. It includes prevention of the fusion of gametes, ecological, behavioral, temporal, and mechanical isolation. Hybrid sterility is the postzygotic isolating mechanism in which the hybrid formed will be sterile and will not be able to reproduce.

Option a. is given as “hybrid sterility”.

As, “hybrid sterility is not a prezygotic isolating mechanism”, is the right answer.

Hence option a. is correct.

Reasons for the incorrect statements:

Option b. is given as “courtship rituals”.

The difference in courtship rituals is due to behavioral isolation which is a prezygotic isolating mechanism. So, it is a wrong answer.

Option c. is given as “habitat separation”.

Habitat separation is due to ecological isolation of species which is a prezygotic isolating mechanism. So, it is a wrong answer.

Option d. is given as “seasonal reproduction”.

Temporal isolation occurs when the species do not mate with each other due to their different reproduction seasons. It is also a prezygotic isolating mechanism. So, it is a wrong answer.

Hence options b., c., and d. are incorrect.

Conclusion

There are two types of reproductive isolating mechanisms: The prezygotic isolating mechanism which prevents the fertilization between species and the postzygotic isolating mechanism that prevents the maturation of hybrid zygote formed by the mating of two different species. These mechanisms are the barriers to facilitate successful reproduction and prevent the exchange of genetic material between species.