Speciation

Question 1

What is a “biological species”?

Answer 1

population of reproducing organisms isolated from other populations. No gene flow between 2 groups= separate species.

Question 2

What are the main problems with the definition for biological species?

Answer 2

It is difficult to apply to prokaryotes and to eukaryotes which are not strictly sexual.
Impossible to apply to extinct organisms.
Difficult to apply to bacteria and archaea with horizontal gene transfer.

Question 3

Define speciation.

Answer 3

The evolution of strong, genetically based isolating barriers between populations that prevent them from interbreeding/ exchanging genes.e.g. habitat differences, mating discrimination, hybrid sterility.

Question 4

How does speciation occur?

Answer 4

Species appear:
in time along a lineage
in space via geographic isolation
various genetic effects may play a role

Question 5

How can speciation be detected?

Answer 5

by comparing populations using population genetics

Question 6

What is allopatric speciation?

Answer 6

Speciation arising due to geographic isolation of two populations.

Question 7

What is parapatric speciation?

Answer 7

Formation of species from population somewhat but not completely geographically isolated. Reproductive barriers evolve with restricted gene flow.

Question 8

What is sympatric speciation?

Answer 8

Splitting of an ancestral species into 2 or more reproductively isolated groups without geographical isolation of the groups. Occurs when there is unrestricted gene flow within incipient species.

Question 9

What is genetic drift?

Answer 9

Random genetic effects can cause massive fluctuations in small populations. Can occur due to founder effects/ bottlenecking events.

Question 10

Define founder effect.

Answer 10

In population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population.

Question 11

Define bottlenecking event.

Answer 11

An event that drastically reduces the size of a population

Question 12

Describe how allopolyploid evolution occurs in plants

Answer 12

failure of cell division after chromosome duplication gives rise to tetraploid tissue. Gametes formed are 2n and can’t fuse with other gametes of the species. If plant reproduces by self-fertilisation and gametes are viable, genetic drift can occur leading to a new species forming.

Question 13

What is disruptive selection?

Answer 13

Natural selection drives the population in 2 different directions at once. If selection is strong enough, it can produce 2 sub-populations and hybrids may suffer reduced fitness- not well-adapted to either resource.

Question 14

What is thought to be the most plausible way for sympatric speciation to occur?

Answer 14

initial partitioning of ecological space followed by mate discrimination; disruptive selection

Question 15

What is the role of genetic factors in speciation?

Answer 15

Sampling and statistical effects such as drift and bottlenecks, combined with long periods of isolation can lead to speciation.

Question 16

Why does speciation often take such a long time?

Answer 16

Partly because natural selection is not directly involved.

Question 17

Why do we have so many species despite speciation taking a very long time?

Answer 17

It is a branching process; ancestral species can split to form many species.

Question 18

What is speciation by reinforcement?

Answer 18

It occurs when previously geographically isolated species come into secondary contact and hybridise. This is where reproductive isolation occurs as a result of natural selection working against hybrids.

Question 19

What is the significance of hybrid zones?

Answer 19

They provide the ideal geographic setting to test if natural selection played a role in the evolution of reproductive isolation in hybridising species.

Question 20

What is a pre-zygotic barrier? Give examples.

Answer 20

reproductive isolation mechanism before mating takes place; deters mating. e.g. pre-mating barriers:
habitat isolation
temporal isolation
behavioral isolation
OR post-mating barriers:
mechanical isolation
gametic isolation

Question 21

What is a post-zygotic barrier? Give examples.

Answer 21

This occurs after mating. Natural selection gets involved by reinforcing species differences. Any individual that can avoid wasteful matings will be at an advantage. e.g. reduced hybrid viability
reduced hybrid fertility
‘hybrid breakdown’ after F2

Question 22

Describe the speciation in blackcaps

Answer 22

• Breeds in central Europe
• Over-winters in Spain, and for last 30 years in UK
• Strong signs of genetic and morphological differences in Spanish and UK populations
• ‘Assortative mating’ – Spanish birds mating with Spanish birds, UK with UK
• Probably due to arrival time on breeding grounds
• Rapid genetic change – raw material of speciation