Lecture 18-19

Question 1

Allopatry

Answer 1

non-overlapping distributions

Question 2

Sympatry

Answer 2

largely overlapping distributions

Question 3

Parapatry

Answer 3

partially overlapping populations

Question 4

Disjunct population

Answer 4

physically separated populations

Question 5

Vagility

Answer 5

the ability of an organism to disperse

Question 6

Deme

Answer 6

a local population of a species

Question 7

Cline

Answer 7

a gradient in the genotype or phenotype of an organism that correlates with the direction or orientation of some geographic feature

Question 8

Extrinsic barrier

Answer 8

a barrier to gene glow caused by factors external to the organism

Question 9

Intrinsic barrier

Answer 9

a barrier to reproductive isolation caused by reproductive isolating mechanisms

Question 10

Pleiotropy

Answer 10

when a single gene product effects multiple phenotype characteristics

Question 11

Introgression

Answer 11

gene flow from one species into another

Question 12

Incipient species

Answer 12

a population that is on its way to becoming a new species

Question 13

Cryptic species

Answer 13

a species complex comprised of multiple, similar species

Question 14

Three steps for speciation

Answer 14

1. isolation of the population: physical (allopatric, parapatric, peripatric) or genetic/ecologcial (sympatric)
2. divergence in traits: adaptation to different habitats or assortative mating/sexual selection
3. establishment of reproductive isolation: reinforcement

Question 15

Allopatric Speciation

Answer 15

• Reproductive isolation, geographically disjunct
• Extrinsic barriers: geographic
• Intrinsic barriers: reproductive isolating mechanisms
• One or more isolating mechanisms
• Extrinsic barriers over time result in intrinsic barriers
• Three types: vicariance, peripatric, and parapatric

Question 16

Vicariance Speciation

Answer 16

Speciation between relatively large population that are geographically separated
Isolated populations tend to differentiate in response to local extrinsic factors
Differential selective forces in demes
Given initial amount of geographic variation, disjunction of populations or groups of populations is likely to result in a cessation of gene flow across the geographic boundary and eventual divergence

Question 17

Factors that influence rate at which new species are formed

Answer 17

• Magnitude of geographic variation
• Organismal vagility
• Magnitude of selection
• Initial variation in population
• Population size

Question 18

Peripatric Speciation

Answer 18

Founder effect, dispersal
Speciation in peripheral populations founded by a small number of individuals
New species will intially appear in marginal/peripheral habitats
Process of speciation may be relatively rapid
Founder Flush cycle

Question 19

Founder Flush Cycle

Answer 19

Drift via Founder effect
Sudden increase in numbers of individuals
Strong selective pressure leads to a genetic bottleneck and crash
Repeat

Question 20

Possible Outcomes when recently diverged populations come into secondary contact

Answer 20

Speciation is complete
Introgression back into a single population
Remain distinct populations that then speciate via reinforcement
Formation of a relatively stable hybrid zone
Formation of a new (third) species in the hybrid zone (homoploid hybrid speciation)

Question 21

Reinforcement

Answer 21

Development of prezygotic isolation mechanisms that prevent the formation of hybrids with reduced fitness and drive speciation to completion

Question 22

Why can selection act against hybrids?

Answer 22

Natural selection produces adaptations to distinct habitats
Sexual selection produced changes in the mating system
Genetic drift led to fixation of alleles that do not work well together when heterozygous

Question 23

Divergence

Answer 23

Interaction between the environment, natural selection, and sexual selection

Question 24

Homoploid Hybrid Speciation

Answer 24

Formation, in the progeny of a natural hybrid, of a new, true-breeding line that is isolated from parental species