Lecture 5- Species and their formation II Flashcards Preview

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Flashcards in Lecture 5- Species and their formation II Deck (62)
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1

Over many generations, what can happen to populations that makes two separated populations reproductively isolated?

Differences accumulate which reduces the probability that members of the two populations could mate and produce viable offspring.

2

Give an example of a species that shows partial reproductive isolation.

Phlux drummondii (garden phlux)

3

How has partial reproductive isolation be achieved in Phlux drummondii?

Plant breeders created many strains by selecting for different characteristics. This inadvertently led to reproductive incompatibility.

4

In experiments, by how much has the reproductive compatibility between different Phlux drummondii strains been reduced?

14-50% (dependent on strains)

5

Why does geographic isolation not necessarily lead to reproductive isolation?

Genetic divergence does not cause reproductive isolation to appear as a byproduct.

6

Give an example of organisms geographically isolated for ~20 million years but are still reproductively compatible.

American and European sycamores- morphologically similar, fertile hybrids.

7

What are the two major groups of mechanisms that may result in reproductive isolation?

Prezygotic reproductive barriers
Postzygotic reproductive barriers

8

At what point do prezygotic barriers operate?

Before fertilisation

9

Name 5 types of prezygotic reproductive barriers.

Habitat isolation
Temporal isolation
Mechanical isolation
Gametic isolation
Behavioral isolation

10

Why does habitat isolation act as a prezygotic barrier?

Individuals of different species live or mate in separate habitats. They may never come into contact with other species during their respective mating periods.

11

Give an example of habitat isolation acting as a prezygotic reproductive barrier.

Rhagoletis pomonella flies in the Hudson River valley

12

How does temporal isolation act as a prezygotic barrier?

Many organisms have short mating periods. If the mating periods of two species do not overlap, they will be reproductively isolated.

13

Give an example of temporal isolation acting as a prezygotic reproductive barrier.

Rhagoletis pomonella flies in the Hudson River valley

14

How does mechanical isolation act as a prezygotic barrier?

Differences in size and shape of reproductive organs prevents gamete union from different species

15

Give an example of mechanical isolation acting as a prezygotic reproductive barrier.

Male insects have elaborate copulatory organs to prevent them inseminating females of other species.

16

How does gametic isolation act as a prezygotic barrier?

Sperm of one species may not attach to the egg of another species because the eggs to not release the appropriate attractive chemicals or the sperm may be unable to penetrate the egg because the gametes are chemically incompatible.

17

How does behavioral isolation act as a prezygotic barrier?

Individuals of a species may reject or fail to recognise individuals of another species as mating partners.

18

Give an example of behavioral isolation acting as a prezygotic reproductive barrier.

Birds of paradise- this led to speciation

19

Give an example of mate choice being mediated by other species.

Whether or not two plant species hybridise depends on food choice of pollinators.

20

How do plants enhance reproductive isolation?

By influencing which pollinators are attracted to the flowers or by alternating when pollen is deposited on the bodies of pollinators.

21

In what flowers has the evolution of floral traits generating reproductive isolation been studied?

Columbines of the genus Aquilegia
Particularly two species:
Aquilegia formosa and Aquilegia pubescens

22

What type of flowers does A.formosa have and what is it pollinated by?

Pendant flowers, short spurs
Hummingbirds

23

What type of flowers does A.pubescens have and what is it pollinated by?

Upright flowers, long spurs
Hawk moths

24

Why do hybrid offspring rarely form between A.formosa and A.pubescens?

Discrimination among flowers by pollinators due to the color that they reflect.
(They attract different pollinators)

25

When do postzygotic barriers act?

After fertilisation, if prezygotic barriers are lacking

26

What are the three ways survival and reproduction of hybrid offspring can be effected?

-Low hybrid zygote viability
-Low hybrid adult viability
-Hybrid infertility

27

Why does natural selection favor prezygotic barriers?

Individuals that mate with individuals of another population will leave fewer surviving descendants then individuals that only mate with their own population

28

Explain how low hybrid zygote viability is a postzygotic barrier.

Hybrid zygotes may fail to mature normally, either dying during development or developing such severe abnormalities that they cannot mate as adults

29

Explain how low hybrid adult viability is a postzygotic barrier.

Hybrid offspring may simply survive less well than offspring resulting from matings within populations.

30

What is hybrid infertility? Give an example.

Hybrids may mature normally, but be infertile when they try to reproduce. For example, horse and donkey offspring, mules, are health but sterile.