Question

Certain reproductive barriers that prevent interbreeding help ensure most species as we know them remain separate species. For each of the following, indicate the type of barrier and explain how it prevents interbreeding. (10 marks total; 2 marks each)

1. A hiney is a cross between a female donkey and a male horse. Like a mule (cross between a female horse and a male donkey), it is sterile.

2. Benthic and limnetic sticklebacks studied by Dr. McPhail and his graduate students can breed, but each type of stickleback prefers to mate with its own type.

3. The shape of a flower allows only certain insects to obtain pollen.

4. Different species of frogs have different mating calls.

5. Different species of pine trees produce pollen at different times of year.

Answer 1

broadly there are two types of reproductive isolation under which different types exist. first is pre-zygotic isolation or barrier and the second one is the post-zygotic barrier. pre-zygotic barrier refers to the isolation before fertilization and post-zygotic refers to the isolation after fertilization.

1. A hinny is a cross between a female donkey and a male horse. Like a mule (a cross between a female horse and a male donkey), it is sterile. - it is an example of a post-zygotic barrier because fertilization has already been done. specifically, the type of reproductive barrier is known as "reduced hybrid fertility" because the offsprings obtained (hinny and mule) are healthy but not fertile.

2. Benthic and limnetic sticklebacks - it is an example of pre-zygotic reproductive isolation because of habitat isolation. benthic sticklebacks live in the open surface of the water and benthic sticklebacks live the bottom of the water.

3. The shape of a flower allows only certain insects to obtain pollen - prezygotic barrier (behavioral isolation) which includes different mating behaviors.

4. Different species of frogs have different mating calls - a prezygotic barrier which includes the behavioral isolation because different species of frogs have some distinguishing vocal cords that produce a different sound that can attract his/her mate only.  

5. Different species of pine trees produce pollen at different times of the year - this is an example of pre-zygotic isolation and specifically the temporal isolation in which organisms are active at different times of the day, month or year.