3: Reproductive isolation

Question 1

Describe prezygotic reproductive isolation + some examples

Answer 1

A barrier before egg and sperm meet
e.g:
- Habitat
- Morphological (different reproductive anatomy)
- Behavioural
- Temporal (different mating seasons)
- Gametic (gamete incompatilibility)

Question 2

Describe postzygotic reproductive isolation + some examples

Answer 2

Barrier after sperm meets egg
Hybrid inviability → hybrids don’t survive
Hybrid infertility → e.g mule
Hybrid breakdown → hybrids are viable and fertile, but are less fit

Question 3

Describe the direct system of how adaptation could lead to reproductive isolation

Answer 3

The same gene is adaptive also affects mating preference
E.g one population favoured for one allele in one environ, another allele favoured in another environ
This could lead to a difference in mate choice = assortative mating

Question 4

Give an example of the direct system of adaption leading to reproductive isolation

(Cichlids)

Answer 4

Seehausen et al. (2008) Cichlids living in different depths
- Blue wavelengths of light in shallow water but not at deeper depths
- Led to divergent selection on visual systems of fish
- Shallow fish sensitive to blue light, deep fish sensitive to red light
- Female (blue light fish) prefer blue coloured males and vice versa (with red)
= led to a prezygotic barrier

Question 5

What is the indirect system of how adaptaion leads to reproductive isolation?

Answer 5

The gene that is adaptive is linked to one which affects mating preference (adaptive and mate choice are on 2 linked loci)

Question 6

Define Magic trait speciation

Answer 6

When natural selection acts on an ecological trait that results in divergence and therefore reproductive isolation

Question 7

What is Haldane’s Rule?

Answer 7

When a cross produces invisible/sterile offspring, the heterogametic sex is more strongly affected

Question 8

How are Haldane’s rule and the Dobshansky-Muller model linked?

Answer 8

Haldane’s rule comes about as a result of Dobzhansky-Muller type processes

Question 9

How much of the genome needs to diverge to cause reproductive isolation?

Describe the Islands of divergence model

Answer 9

→ ‘Island’ regions without gene flow will grow over time
- Could initially arise from just a small no. of genetic regions that differ between 2 populations
- These differences could cause ecological differences that adapt them to different environments and grow

Question 10

Describe what speciation genes are, and why duplication genes might be good candiates.

Answer 10

Genes will cause reproductive isolation almost in the absence of anything else
- Duplication genes might be good candidates because they rapidly evolve new roles