R25 Speciation

Question 1

What is the morphological species concept ?

Answer 1

groups of organisms that appear identical by anatomical criteria, oldest and most practical concept.
- Sometimes highly misleading as some species mimic each other

Question 2

What is the biological species concept ?

Answer 2

species are group of interbreeding natural populations that are reproductively isolated from other such groups

Question 3

Whats wrong with the biological species concept ?

Answer 3

• Does not apply to asexual organisms
• Impossible to test
• Impossible to classify extinct taxa
• Often violated, many good species still hybridise

Question 4

What is the null model of speciation ?

Answer 4

Bateson-Dobzhansky-Muller incompatibilities) (BDMI):

Population 1 and 2 separated by space (allopatry)
Each population accumulates mutations at different loci
New mutations arise and fix in both populations
The combination of the new alleles in the F1 would be incompatible e.g., reduce hybrid fitness

Assumes that the only barriers between species are BDMIs

Question 5

What are some types of islands ?

Answer 5

Types of islands (isolated areas):
- Freshwater lakes and ponds
- Mountain tops (sky islands)

Question 6

What genes are involved in BDMI ?

Answer 6

• Oncogenes Tu (duplicate of dermal growth factors)
• Repressors R
• F2 Tu/-; -/- develops malignant melanoma, reduced viability

Question 7

What are some prezygotic barriers ?

Answer 7

• Mate recognition: behaviour, timing, mate recognition
• Mate barriers: physical, behavioural
• Post mating prezygotic barriers: egg-sperm interaction
• Temporal isolation
• Host plant they live on
• Mate choice via accustic
• Chemical cues
• Visual cues

Question 8

What is some postzygotic barriers ?

Answer 8

• F1 viability and fertility

Prezygotic barriers act earlier and so contribute more to reproductive isolation than BDMIs

Question 9

Why and how do prezygotic barriers evolve?

Answer 9

• They evolve as a by-product of strong divergent selection
  o Flies decide to change fruit they eat, temporally and spatially isolated – adapting to a different niche will lead to evolution of prezygotic barriers
• Reinforcement: prezygotic isolation is under direct selection
  o Prezygotic isolation evolves more quickly than postzygotic isolation
  o Sympatric pairs have greater prezygotic isolation than allopatric pairs
  o Prezygotic isolation evolved to prevent individuals wasting reproductive effort in unfit hybrids

Question 10

What is BDMIs ?

Answer 10

negative epistasis

Question 11

When is speciation complete?

Answer 11

When speciation is complete there can’t be any further genetic crosses, requires incomplete postzygotic isolation

Question 12

What is reinforcement ?

Answer 12

Reinforcement can only occur when natural selection acts against hybrids.
- Sympatric pairs shows greater pre-zygotic isolation than allopatric pairs

Question 13

What is character displacement ?

Answer 13

When one phenotype is selected to avoid overlapping niches

Question 14

Does sympatric or allopatric pairs show greater pre-zygotic isolation ?

Answer 14

Sympatric pairs show greater pre-zygostic isolation than allopatric pairs

Question 15

Does prezygotic or postzygotic barriers contribute more to reproductive isolation than BDMIs ?

Answer 15

prezygotic

Question 16

How can pre-zygotic isolation evolve ?

Answer 16

I) as a by-product of divergence in microbiomes i) as a by-product of strong ecological selection ii) through direct selection reinforcement (requires existing BDMIs)