org. evolution - CH16 - speciation

What is the effect of gene flow on populations?

Gene flow is a homogenizing force that reduces differences between populations

What evolutionary forces promote divergence between populations?

• Natural selection

• Genetic drift

• Sexual selection

What happens when gene flow is reduced or absent?

Populations diverge genetically

What happens when gene flow increases between populations?

Populations become more similar (homogenization)

What are the three possible outcomes when two populations come back into contact (hybrid zone)?

• Reinforcement

• Fusion

• Stability

Define sympatric speciation.

Speciation that occurs in the same geographic location without physical separation

What must occur for sympatric speciation to happen?

Reproductive isolation must evolve (behavioral, temporal, etc.)

What is polyploidy?

A multiplication of chromosome number that can cause instant reproductive isolation

In what organisms is polyploidy most common?

Plants

Why does polyploidy lead to speciation?

It creates immediate reproductive isolation from the original population

What is ecological speciation?

Speciation driven by divergent natural selection in different environments

What type of selection is commonly involved in ecological speciation?

Disruptive selection

How can ecological speciation lead to reproductive isolation?

Differences in environment → differences in traits → temporal or behavioral isolation develops

What is temporal isolation?

Populations reproduce at different times, preventing interbreeding

Can speciation occur even with gene flow?

Yes — if selection is strong enough, divergence can still occur

What experiment showed that divergence can occur despite gene flow?

Endler (1973) Drosophila experiment

What is speciation driven by sexual selection?

Speciation caused by differences in mate preference

How can sexual selection reduce gene flow?

Individuals prefer certain traits → they stop mating with others → isolation

Give an example of speciation by sexual selection.

African cichlid fish in Lake Victoria

What trait mainly differs among African cichlid species?

Male coloration

Why are African cichlids reproductively isolated?

Female mating preferences for specific male colors

What happens to mate choice under different light conditions in cichlids?

• Normal light → assortative mating (same species)

• Monochrome light → random mating

What environmental factor influenced cichlid speciation?

Light differences in water depth affecting color perception

What is the effect of eutrophication on speciation?

Can lead to hybridization and loss of biodiversity

What determines whether populations diverge or stay similar?

The balance between gene flow and selection/drift/sexual selection

What causes genetic differences to accumulate between geographically isolated populations?

A. Mutations
B. Natural selection
C. Genetic drift
D. Sexual selection
E. All of the above

E

What is a condition that prevents isolated populations from mixing again, once the geographic barrier is removed?

A. Anatomical incompatibility
B. Gene flow
C. Both

A

What is a shortcoming of the biological species concept?

A. It is more subjective than the other concepts.
B. It cannot distinguish cryptic species.
C. It is not applicable to asexual species.
D. It only works for extinct species.

C

According to Coyne, what is the most common cause of speciation?

A. Geographic isolation
B. Sexual selection
C. Natural selection
D. Temporal isolation
E. Hybrid sterility

A

What evidence did Coyne give for the claim that allopatry is the predominant mode of speciation?

A. Groups that have been isolated for longer periods display greater genetic dissimilarity.
B. Closest living relative species are usually non-overlapping.
C. Many hybrids are infertile

B

What REDUCES genetic variation between populations?

A. Behavioral isolation
B. Sexual selection
C. Genetic drift
D. Gene flow
E. All of the above

D

Two isolated lakes are invaded by a species of leech. In lake 1, the leeches produce 70% females, and in lake 2, the leeches produce 50% females. Assuming all else is equal, which leech population size should grow the fastest?

A. Lake 1’s
B. Lake 2’s
C. They should grow at the same rate

A

Which pair of populations is likely to show the greatest genetic divergence?

A. A pair that has been partly isolated for 2 mil years with 9% gene flow during that time.
B. A pair that has been partly isolated for 0.5 mil years with 30% gene flow during that time.
C. A pair that has been partly isolated for 3 mil years with 4% gene flow during that time.

C

According to Coyne, what is the most common cause of sympatric speciation?

A. Behavioral isolation
B. Sexual selection
C. Polyploidy
D. Temporal isolation
E. Hybrid sterility

C

Why can’t a polyploid plant mate with its diploid individuals from its parent population?

A. They release pollen at different times
B. They don’t attract the same pollinators
C. Their offspring would end up with an odd number of chromosomes

C

What conclusion about divergence can we draw from this data?

A. 40% gene flow is a stronger force than the artificial selection.
B. Artificial selection is a stronger force than 40% gene flow.
C. The relative influences of artificial selection and 40% gene flow on divergence are approximately the same.

B

Studies have shown that female zebrafish strongly prefer genetically modified red fluorescent Glofish® males to wildtype males. Is this evidence for the good genes hypothesis?

A. Yes
B. No

B

What conclusion can we draw from this data? D score represents responsiveness to red male minus responsive to blue male, where positive values = red preference and negative values = blue preference.

A. The mono light makes each female prefer its own type as a mate.
B. The mono light makes each female prefer the other type as a mate.
C. The mono light makes each female prefer the blue type as a mate.

C

Given the results of that study, what would be the most likely effect of eutrophication, leading to cloudy water within the east African lakes?

A. Fewer species of cichlid
B. More species of cichlid
C. No change in number of cichlid species

A