Species and Speciation

Question 1

Define biological species concept and give its limitations

Answer 1

Interbreeding organisms that produce fertile offspring and evolve independently of other populations.

Does not include asexually reproducing organisms, cannot be applied to fossils or geographically separated populations, incomplete knowledge of species that may interbreed successfully.

Question 2

What are other species concepts and their limitations?

Answer 2

Phylogenetic - ancestral analysis - few complete phylogenies available, doesn’t address mechanism.

Morphological - differences in morphology - subjective criteria and interspecies variation often higher than intra

Ecological - based on environmental context - niche hard to characterize

Question 3

What are the prezygotic isolating mechanisms and an example of each?

Answer 3

Potential mates don’t meet in space or time (seasonal/habitat)

Potential mates meet but don’t mate (ethological)

Mating attempted but no zygote formed (mechanical)

Question 4

What are the postzygotic isolating mechanisms, how do they occur and what is an example of each?

Answer 4

Due to sufficient genetic divergence of isolated populations.

Gametic mortality

Zygote mortality

Hybrid inviability

Hybrid sterility

Question 5

How do gene incompatibilities lead to genetic isolation?

Answer 5

Mutant alleles at different loci could be incompatible. If they become fixed, reproductive isolation occurs.

Question 6

What are sympatric, allopatric and parapatric species?

Answer 6

Sympatric - occur in same geographical area.

Allopatric - occupy different geographic areas and don’t meet.

Parapatric - only meet along borders of their ranges.

Question 7

What is anagenesis? Cladogenesis?

Answer 7

Anagenesis - one species gradually turns into the other

Cladogenesis - one species give rise to two or more species

Question 8

What are the two sources of hybrid sterility, what are they and what are examples of each?

Answer 8

Chromosomal - improper pairing due to differing chromosome structure (gametes have incomplete complements of genes).

Genic - genetic composition too different

Question 9

What is a hybrid zone?

Answer 9

Zone of interbreeding species

Question 10

What would you predict if hybrid fitness is lower than either parent fitness?

Answer 10

• A very narrow hybrid zone

- Reinforcement

Question 11

What would you predict if hybrid fitness is higher than either parent?

Answer 11

Can lead to extinction of the species with lower fitness

Question 12

What is reinforcement?

Answer 12

Reinforcement occurs when natural selection favors the traits in two distinct populations over maladaptive hybridization

Question 13

What is a cline?

Answer 13

Gradual change over a gradient

Question 14

What is geographic variation?

Answer 14

When a trait varies in different geographic areas of the same species.

Question 15

What is an ecotype? Give an example.

Answer 15

Gradient of variation of a short transect.

Example: High and low altitudes variants of a trait in a species that occupies both

Question 16

What is character displacement? Give an example.

Answer 16

Character displacement is the phenomenon where differences among similar species whose distributions overlap geographically are accentuated in regions where the species co-occur, but are minimized or lost where the species’ distributions do not overlap.

Example: Three-spined stickleback, limnetic and benthic type and hybrids are selected against but intermediate form is present when there is only one species in a lake.

Question 17

What are the three main types of variation within populations?

Answer 17

Morphological

Genetic

Behavioral

Question 18

What are two modes of polymorphism in an evolving population?

Answer 18

Transitional - one allele replacing the other

Balanced - stable intermediate frequency

Question 19

Is phenotypic variation necessary for genetic variation?

Answer 19

No, genetic variation can be latent.

Question 20

How could you identify a variant gene locus in a protein?

Answer 20

By finding an invariant enzyme that corresponds to it.

Question 21

What is linkage disequilibrium? How is it determined? How does it happen? What eliminates it? Why is it important?

Answer 21

Nonrandom association of alleles at different loci in a given population.

If the frequency of association is higher or lower than would be expected if the alleles were independent/randomly associated.

Natural selection - selective sweeps; random genetic drift, onset of populations interbreeding

Eliminated by recombination, which breaks down non-random genetic associations.

It causes alleles to deviate from expected frequencies, can slow evolutionary change, can also maintain specific allele combinations.

Question 22

What is coadaptation?

Answer 22

Adaptive combination of alleles at various loci

Question 23

What three steps are involved in speciation?

Answer 23

Genetic isolation, genetic divergence and then maintaining reproductive isolation.

Question 24

Describe how allopatric speciation occurs. What are the two main types of allopatric speciation?

Describe how sympatric speciation occurs.

Describe how parapatric speciation occurs.

Answer 24

Allopatric - populations become geographically isolated so gene flow ceases. Genetic divergence through evolution leads to independently evolving populations. Examples: dispersal/colonization and vicariance. Organism example: Hawaiian Drosophila

Symaptric - divergent natural selection overwhelms gene flow. Mechanisms that reduce gene flow and allow this to occur are spatial, temporal and behavioral isolation, also polyploidy.

Parapatric - Reproductive isolation occurs with limited gene flow. Organism example: ring species CA salamanders

Question 25

How does polyploidy lead to speciation?

Answer 25

If for example you have a tetraploid plant that turns up in a diploid population because it has meiosis separation errors, it produces 2n eggs and sperm, which will create more tetraploids that cannot interbreed with the rest of the diploids, thus creating a new ‘species’.

Question 26

What is vicariance?

Answer 26

When a geographic range is split into two distinct populations.

Question 27

What is assortative mating?

Answer 27

A mechanism whereby organisms with a given trait tend to choose mates with the same trait, which can also lead to reproductive isolation.

Question 28

Who came up with the biological species concept and when?

Answer 28

Mayr, 1940.

Question 29

What is secondary contact? What can it lead to?

Answer 29

Parental lineages make contact after a period of isolation, can lead to hybrid zones.

Question 30

Nonrandom mating affects genotype frequencies because…

Answer 30

desirable traits that mating partners select for are likely to increase in frequency.

Question 31

Sexual reproduction increases variation because….

Answer 31

it creates more combinations of alleles.

Question 32

Linked genes and linkage equilibrium arise because..

Answer 32

selection can favor certain combinations of alleles.

Question 33

Linkage disequilibrium affects evolution by….

Answer 33

slowing selection on independent alleles.

Question 34

Does inbreeding increase or decrease the frequency of heterozygotes in a population?

Answer 34

Decreases.