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Ecology and diversity > Lecture 5- Species and their formation II > Flashcards

Lecture 5- Species and their formation II Flashcards

1
Q

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

A

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

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2
Q

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

A

Phlux drummondii (garden phlux)

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3
Q

How has partial reproductive isolation be achieved in Phlux drummondii?

A

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

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4
Q

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

A

14-50% (dependent on strains)

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5
Q

Why does geographic isolation not necessarily lead to reproductive isolation?

A

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

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6
Q

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

A

American and European sycamores- morphologically similar, fertile hybrids.

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7
Q

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

A

Prezygotic reproductive barriers

Postzygotic reproductive barriers

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8
Q

At what point do prezygotic barriers operate?

A

Before fertilisation

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9
Q

Name 5 types of prezygotic reproductive barriers.

A 
Habitat isolation
Temporal isolation
Mechanical isolation
Gametic isolation
Behavioral isolation
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10
Q

Why does habitat isolation act as a prezygotic barrier?

A

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

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11
Q

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

A

Rhagoletis pomonella flies in the Hudson River valley

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12
Q

How does temporal isolation act as a prezygotic barrier?

A

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

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13
Q

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

A

Rhagoletis pomonella flies in the Hudson River valley

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14
Q

How does mechanical isolation act as a prezygotic barrier?

A

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

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15
Q

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

A

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

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16
Q

How does gametic isolation act as a prezygotic barrier?

A

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.

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17
Q

How does behavioral isolation act as a prezygotic barrier?

A

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

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18
Q

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

A

Birds of paradise- this led to speciation

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19
Q

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

A

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

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20
Q

How do plants enhance reproductive isolation?

A

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

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21
Q

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

A

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

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22
Q

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

A

Pendant flowers, short spurs

Hummingbirds

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23
Q

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

A

Upright flowers, long spurs

Hawk moths

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24
Q

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

A

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

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25
Q

When do postzygotic barriers act?

A

After fertilisation, if prezygotic barriers are lacking

26
Q

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

A
  • Low hybrid zygote viability
  • Low hybrid adult viability
  • Hybrid infertility
27
Q

Why does natural selection favor prezygotic barriers?

A

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

28
Q

Explain how low hybrid zygote viability is a postzygotic barrier.

A

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

29
Q

Explain how low hybrid adult viability is a postzygotic barrier.

A

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

30
Q

What is hybrid infertility? Give an example.

A

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

31
Q

What is strengthening of prezygotic barriers known as?

A

Reinforcement

32
Q

Explain how the hypothesis that Phlox drummondii has red flowers only where it is sympatric with pink flowered P.cuspidata because having red flowers decreases interspecific hybridisation can be tested expermientally.

A
  1. Introduce equal numbers of red and pink P. drummondii into an area with P.cuspidata
  2. After flowering season ends, assess genetic composition of seeds produced by P.drummondii of both colours
33
Q

In the experiment where Phlox drummondii was introduced to areas with P.cuspidata, what were the results?

A

Seeds produced by pink flowers were 38% hybrid

Seeds produced by red flowers were 13% hybrid

34
Q

What can be concluded from the experiment on P.drummondii living sympatrically with P.cuspidata?

A

Having flowers that differ in colour from those of P.cuspidata reduces interspecific hybridisation

35
Q

How does having red flowers serve as a prezygotic barrier for P.drumonddi?

A

Pollinators tend to visit flowers of only one colour

36
Q

How can reinforcement be detected using comparative methods?

A

If reinforcement is occurring, sympatric pairs of closely related species evolve prezygotic reproductive barriers more rapidly than allopatric species

37
Q

Give an example of species where comparative methods demonstrate reinforcement.

A

Agrodiaetus butterflies- colours of wings females choose males by has diverged more rapidly in sympatric than allopatric populations

38
Q

What condition is required for hybrid zones to form?

A

Incomplete reproductive isolation

39
Q

What happens if hybrid offspring of two populations coming together are as fit as those from mating within each population?

A

Hybrids spread through both populations and reproduce. Gene pools are combined. No new species result.

40
Q

What happens when hybrid of two populations coming together are less fit?

A

Complete reproductive isolation may evolve due to reinforcement

41
Q

What happens if two populations come together and hybrid zones are at some disadvantage?

A

A narrow hybrid zone may exist as reinforcement does not happen, or the zone may persist for a long time while reinforcement is developing

42
Q

Name the flowers from the experiment.

A

Phlox drummondii

P.cuspidata

43
Q

What do hybrid zones contain?

A

Recombinant individuals resulting from many generations of hybridisation

44
Q

What hybrid zone has been well studied?

A

Bombina European toads
Bombina bombina- fire bellied toad
Bombina variegata- yellow bellied toad

45
Q

Where does B.bombina live?

A

Eastern Europe

46
Q

Where does B.variegata live?

A

western and southern Europe

47
Q

Where is the hybrid zone of bombina toads in europe?

A

4800 km from eastern germany to the black sea

48
Q

What is the result of hybrids between fire and yellow bellied toads?

A

Hybrids have a range of defects, many lethal.

Skeletal abnormalities, mishapen mouths, fused ribs, reduced number of vertebrae

49
Q

Why is the hybrid zone narrow?

A

There is strong selection against hybrids

50
Q

Why do hybrid zones persist?

A

Pure bred individuals move only a short distance into the zone and have not previously encountered the other species so reinforcement has not evovled

51
Q

What other factors can cause hybrid zones to develop?

A

Human activity.

52
Q

Give an example of a hybrid zone that is a result of human activity.

A

Habitat disruption has created a hybrid zone between two Banksia species in Australia. The flowering seasons have expanded and overlapped.

53
Q

What 5 factors can effect the rate of speciation?

A
  • Number of species
  • Dispersal abilities
  • Diets
  • Mechanism of pollination
  • Sexual selection
54
Q

How does dispersal rate effect the rate of speciation?

A

Speciation rate is higher in species with poor dispersal abilities because even narrow barriers can divide the species

55
Q

Give an example of poor dispersal abilities leading to speciation.

A

Land snails on the Hawaiin islands restricted to a single valley- snails move short distances do valleys effectively act as a barrier to dispersal

56
Q

In what way does diet effect the rate of speciation?

A

Populations with specialised diets are more likely to diverge

57
Q

Give an example of diet effecting speciation rate.

A

True bugs- hemipterans, ancestor was a predator- eats many species of insects. dietary shift evolved at least twice to herbivory. Herbivorous groups have many more species because they specialize on species of plants.

58
Q

How does pollination effect the rate of speciation?

A

Speciation occurs more in insect-pollinated plants than wind pollinated plants

59
Q

Why does speciation occur more in insect-pollinated plants than wind pollinated plants?

A

Restrictions on the number of pollinator species that can visit the flower, increasing reproductive isolation opportunities

60
Q

Give an example of insect-pollinated plants leading to speciation.

A

columbines (Aquilegia)- rate of evolution is 3x faster in long nectar spurs because of restriction of pollinator species that can visit the flower

61
Q

How does sexual selection lead to speciation rates being higher?

A

Animals with complex sexually selected behaviors are likely to form new species because they make sophisticated discriminations among potential mating partners

62
Q

In what species can a high rate of speciation be seen?

A

Birds of paradise- there are 33 species because of their promiscuous mating system.
Comparatively, Manucodes have 5 species and form monogomous mating bonds.

Ecology and diversity (17 decks)

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