Speciation

Question 1

Allopatric speciation

Answer 1

• split habitat prevents gene flow
• founder/bottleneck effect: sudden drop in population causes a new allele distribution

Question 2

Selection effects

Answer 2

• directional: from one end to the other
• disruptive: centralized alleles are less frequent, periphery is more frequent
• stabilizing: already frequent allele becomes more stable

Question 3

Sympatric speciation

Answer 3

• same habitat, but ecological adaptations/behavior changes lead to reproductive isolation
• e.g. blackcap birds breed in EU and migrate to Spain in the winter; NOW, some move up to UK , due to assortative mating effects
• would mean that natural selection is directly acting on a population to encourage reproductive isolation
• history: allopatric speciation period must be highly unlikely

Question 4

Why are there so many species?

Answer 4

• ecological changes might introduce new niches
• mating isolation by time/method

Question 5

Pre/postzygotic barriers

Answer 5

• pre: habitat, temporal, behavioral, mechanical, gametic
• post: reduced hybrid viability, fertility issues, hybrid breakdown in F2 or later

Question 6

Hybrid zones (what are they; 3 types?)

Answer 6

• regions where genetically distinct populations meet and reproduce
  1. FUSING: high gene flow and interfertility -> new species
  2. REINFORCEMENT: mating results in loss of fitness, so speciation is reinforced
  3. STABILITY: limited gene flow, negligible effects, little change

Question 7

What reinforces inviability between carrion and hooded crows?

Answer 7

Inverted chromosome regions make it so that crossing over is prohibited. When they do occur, genetic information is likely to remain linked.

Question 8

Phlox and cline theory

Answer 8

• evidence of stronger reproductive isolation in sympatric conditions by difference in flower color
• cline theory: stronger natural selection means phenotypic changes are more geographically abrupt