Speciation

Question 1

What leads to the overall changes of traits in evolution?

Answer 1

Evolution takes place by the gradual accumulation of beneficial mutations​.
Beneficial mutations are selected for, detrimental mutations are selected against.
evolution works on individuals to create species.

Question 2

What is a species (breeding)?
What are other species concepts?

Answer 2

Groups of interbreeding natural populations that are reproductively isolated from other such groups”​
Species ≈ Gene pool ​
The gene pool / species is the unit of evolution​
(Individuals are the unit of selection)​

*Recognition species concept​
*Ecological species concept​
*Phenetic species concept​

Question 3

What is speciation?

Answer 3

Reproductive isolation is the crucial event​
​1. A single species made up of interbreeding individuals​
2. A genetic variant spreads through the species; variant ‘b’ only mates with other variant ‘b’​

Question 4

What is Allopatric speciation​

Answer 4

New species forms geographically apart from its ancestor​.

1. A new physical barrier could divide the geographic range​
2. This would prevent (or slow down) gene-flow between isolated populations​
3. Different selection pressures, different random mutations, genetic drift​
4. Full reproductive isolation​

Question 5

What is a cline

Answer 5

‘Cline’: gradient of continuous genotypic or phenotypic variation within a species​

Question 6

What are bergmann’s and Allens’s rule?

Answer 6

Bergmann’s rule states that organisms at higher latitudes should be larger and thicker than those closer to the equator to better conserve heat, and Allen’s rule states that they will have shorter and thicker limbs at higher latitudes.

Question 7

What is a ring species and give an example?

Answer 7

A ring species is where two populations which do not interbreed are living in the same region and connected by a geographic ring of populations that can interbreed.

Ring species show that geographic variation can lead to the formation of new species​
e.g the green warbler (courtship song changed)

Question 8

What can speed up​ allopatric speciation?

Answer 8

reinforcement are selected to avoid hybridization should have greater fitness​
Individuals that mate with their own lineage will be selected for​
Reinforcement = assortative mating​ (such as only mating with others of similar size)

Question 9

describe allopatric speciation in a ‘Peripheral isolate’​

Answer 9

A small population at the edge of the species range is isolated​
Extreme conditions​
Rapid evolution​
Sometimes called ‘Peripatric speciation’​

Question 10

Allopatric speciation and ‘Founder effects’​

Answer 10

*Loss of genetic variation​
*Speciation is not adaptive​ (could be genetic drift or selection) but it’s a controversial idea​.
e.g. Recently evolved fruit flies in Hawaii show same genetic diversity as older species​

Question 11

Describe Parapatric speciation​?

Answer 11

*New niche or range with different conditions and selection pressures​
*Reinforcement​ (preference)
*But no physical barrier​
New species forms within a contiguous population​

Question 12

What are Stepped clines and hybrid zones​

Answer 12

Hybrid zones could indicate a parapatric speciation event​
But could also be due to allopatric species meeting​
A ‘stepped cline’ compared to a normal smooth cline (b)​
species 1
hybrids
species 2

Question 13

What is Sympatric speciation​ and give an example?

Answer 13

New species forms in geographical range of ancestor​ this can be explained by behavioral differences
*A stable polymorphism​
*Reinforcement (assortative mating)​

Speciation in cichlids​=Not isolated, but 300 species in lake Victoria​ as feeding polymorphism​ which was reinforced by assortative mating​.