Geography of Species

Question 1

What are modes of speciation?

Answer 1

The geographic context that gives rise to speciation

Question 2

What are the 3 modes of speciation?

Answer 2

Allopatric - species geographically isolated with no gene flow
Parapatric - species close together limited gene flow
Sympatric - free gene flow in a population in which divergence occurs

Question 3

What three things did Mayr note when studying island species?

Answer 3

1. Reproductive isolation involves many factors
2. New forms of a species are usually found in particular locations
3. Genes causing reproductive isolation are unlikely to spread within a population

Question 4

What is the geographic/allopatric model of speciation?

Answer 4

Assumes that speciation occurs when a species is split into geographical sub-population and these subpopulations undergo selection and drift with limited gene flow so that they can no longer interbreed

Question 5

What issues are there with Mayr’s model of geographic speciation?

Answer 5

Describes geographic isolation as happening due to dramatic geographical events and while these do occur, climate change (glaciation) has probably been more important

Question 6

What is phylogeography?

Answer 6

The study of patterns of geographic variation within closely-related species

Question 7

What is the peripheral isolates model of speciation?

Answer 7

Assumes that the most important changes occur in populations on the periphery of species ranges

Question 8

Why might PI populations be more likely to have “pioneer” genotypes?

Answer 8

Selection could be more intense and in a more unusual direction

Question 9

Give 3 reasons as to why founder effects are important

Answer 9

• Genetic drift could change gene frequencies dramatically
• Can fix unusual forms/deleterious genes
• Weird sexual selection

Question 10

In what two ways may parapatric speciation emerge?

Answer 10

• When there is differentiation along an ecotone

- When there is secondary contact between forms that started to diverge in allopatry

Question 11

What evidence is there between the evolution of reproductive isolation between ecotypes?

Answer 11

• Metal tolerant and pasture ecotypes have developed flowering periods that are a week apart

Question 12

Define the Wallace effect

Answer 12

When selection against hybridisation could exaggerate sexual differences so that species no longer interbreed

Question 13

Why is sympatric speciation so controversial?

Answer 13

• Doubt on how genes causing unfitness could spread throughout a species
• Muller proposed that genes could evolve independently and have negative interactions

Question 14

How have Bush and colleagues argued for sympatric speciation?

Answer 14

• Investigating American apple maggot fly Rhagoletis pomonella which infects either apple plants or hawthorn plants
• Argues that both pre and post-mating isolation would build up due to adaptation to alternative hosts
• Some proof of genetic differences