Allopatric vs. Sympatric Speciation and Hybrid Zones

Question 1

Speciation

Answer 1

• the orgin of new species
• at the focal point of of evolutionary theory

Question 2

Allopatric speciation

Answer 2

• Geographically separate populations may evolve independently through mutation, natural selection, and genetic drift
• Gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations
• even if contact is restored between populations, interbreeding is prevented

Question 3

Sympatric Speciation

Answer 3

• a reproductive barrier isolates a subset of a population without geographic separation from the species
• occurs when gene flow is reduced

Question 4

What are the three ways in which gene flow is reduced?

Answer 4

o polyploidy- presence of extra sets of chromosomes due to accidents during cell division (more common in plants than animals- cotton, potatoes)
o habitat differentiation- sympatric speciation can also result from the appearance of new ecological niches (North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees)
o sexual selection- natural selection arising through preference by one sex for certain characteristic in individuals of theother sex (sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in lake Victoria)

Question 5

Sympatric vs. Allopatric Speciation

Answer 5

• allopatric- population geographically divided
• sympatric- reproductive barrier isolates population
• both give rise to new species that cannot interbreed

Question 6

Hybrid

Answer 6

• the offspring of crosses between different species
• for example: a mule is the offspring of a male donkey and a female horse

Question 7

Hybrid zone

Answer 7

• a region in which members of different species mate and produce hybrids
• can occur when adjacent species meet

Question 8

What are the possible outcomes when closely related species meet in a hybrid zone?

Answer 8

• strengthening of reproductive barrier
• weakening of reproductive barrier
• continued formation of hybrid individuals

Question 9

Polyploidy

Answer 9

o the presence of extra sets of chromosomes due to accidents during cell division (more common in plants than animas- cotton, potatoes)

Question 10

Habitat differentiation

Answer 10

• the appearance of new ecological niches (North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees)