Multivariate evolution

Question 1

Define a univariate character.

Answer 1

Isolated traits with ‘one dimension’, e.g. number of bristles on a drosophila.

Question 2

Univariate characters follow a continuous distribution. True or false?

Answer 2

True.

Question 3

Univariate traits respond predictably to selection. True or false?

Answer 3

True.

N.B. if the phenotype is not genetically determined you will not see a response to selection.

Question 4

Define a multivariate trait.

Answer 4

Traits that have multiple dimensions.

Question 5

Give an example of a multivariate trait.

Answer 5

The condition-dependent trait of male eye stalk length in stalk-eyed flies.

Question 6

Multivariate characters are often linked. Why?

Answer 6

Because the same gene has more than one effect, thus the traits share genes.

Question 7

Give an example of linked multivariate characters.

Answer 7

Hair and eye colour.

Question 8

In univariate characters, the stronger the selection the greater the change in trait value. Give the equation that represents this.

Answer 8

Δz = σ2A x β

Δz = change in trait value
σ2A = additive genetic variance 
β = strength of selection

Question 9

With multivariate traits, there is interference between traits when there is covariance. True or false?

Answer 9

True.

Question 10

What is a ‘correlated response’ with regard to multivariate traits?

Answer 10

If one trait is selected for then they all change.

Question 11

What does it indicate about the covariance between traits if correlation is positive?

Answer 11

Covariance is also positive.

Question 12

What is an ‘accelerated response’?

Answer 12

When there a positive correlation and selection is also positive.

Question 13

What is an ‘adaptive conflict’?

Answer 13

When there is a positive correlation but selection is opposed.

Question 14

What role do multivariate traits have in sexual dimorphism?

Answer 14

The selection of one traits affects the selection of other traits, causing evolution of different forms.

Question 15

In males there is a linear pattern between the number of matings and the number of offspring. Is this true for females?

Answer 15

No - females can only fall pregnant a limited number of times per year. Thus more matings does not produce more offspring.

Question 16

What are the reproductive roles of a) males and b) females?

Answer 16

a) To acquire mating partners

b) To turn resources into offspring

Question 17

Males and females face opposing selection pressures. Give an example of this in drosophila.

Answer 17

Fast females are selected against, fast males are selected for. Fast females waste energy so can convert less energy into offspring. Fast males are more likely to find a mate if they move around a lot.

Question 18

Define sexual antagonism.

Answer 18

Where there is adaptive conflict between the sexes in that a new mutation is beneficial to one sex but deleterious to the other.

Question 19

If mutations are sexually antagonistic, when do they invade?

Answer 19

If the benefits outweigh the costs.

Question 20

Mutations that break down genetic correlation lead to sex-specific gene expression, meaning the sexes evolve apart. What is genetic correlation?

Answer 20

Genetic correlation is a measure of much genes are shared. Genes are shared between the sexes on the autosomes.

Question 21

Mutations that break down genetic correlation lead to sex-specific gene expression. Explain what happened with the X and Y chromosomes.

Answer 21

The Y underwent a series of inversions which now means it mostly cannot recombine with the X, thus genetic correlation has been broken.