Phenotypic plasticity

Question 1

Define phenotypic plasticity.

Answer 1

When the phenotype changes in response to the environment.

Question 2

Define a norm of reaction.

Answer 2

The normal outcome we expect to see in a particular trait.

Question 3

To assess norms of reaction we use half-sib families, i.e. all the progeny have the same father but different mothers. Why?

Answer 3

Then there is a known average relatedness between sibs and we can compare outcomes.

Question 4

Variance between half-sib families is an estimate of additive variance. True or false?

Answer 4

True.

Question 5

Why is the variance between half-sib families is an estimate of additive variance?

Answer 5

Covariance between half sibs is 1/4VA. Thus multiplying the answer by 4 estimates VA.

Question 6

Describe the diagrams that show norms of reaction. What do a) the vertical axes and b) the horizontal lines represent?

Answer 6

a) Both vertical axes represent a separate environment

b) The horizontal lines represent the phenotypes of different families for a trait

Question 7

What does it mean if a horizontal line meets both vertical axes at the same point?

Answer 7

There is no phenotypic plasticity displayed by that family for that trait as the phenotype is the same in both environments.

Question 8

What does it mean if all the horizontal lines are on top of each other?

Answer 8

There is no variance in phenotype between families.

Question 9

What does it mean if all the horizontal lines are spread?

Answer 9

There is variance.

Question 10

What does it mean if a horizontal line is sloped?

Answer 10

There is high plasticity as there is disparity in value between the environments.

Question 11

What does it mean if all the horizontal lines are parallel and sloped to the same degree?

Answer 11

There is no variation in phenotypic plasticity. All the families react in the same way in response to a changing environment.

Question 12

What does it mean if the horizontal lines cross over? Give 2 explanations.

Answer 12

1. That the phenotypic rank of each family differs drastically in each environment
2. That each family reacts differently to the differing environments. This implies a genetic component to variation.

Question 13

2-way ANOVAs are used to analyse reaction norm diagrams. Interaction between genes and the environment give evidence for what?

Answer 13

Additive variance for plasticity, shown when different genotypes respond differently to the same environment.

Question 14

In stalk-eyed flies, females prefer males with larger eye stalks, however they cannot fly well. Why then do females select for this?

Answer 14

Because large ornaments are costly to produce. If a male can afford to produce such ornaments he must have good genes.

Question 15

Eye stalks in males are an example of a condition dependent trait. Define a condition dependent trait.

Answer 15

A trait that is only expressed under a particular fitness condition, e.g. males can produce large ornaments if they have good genes.

Question 16

What happens to the variance in condition dependent traits in benign environments and why?

Answer 16

The variance is lower because the cost differential is lower. If the environment is benign selection does not act as strongly and individual differences in quality are masked.

Question 17

What happens to the variance in condition dependent traits in harsh environments and why?

Answer 17

The variance is higher because the cost differential is higher. If the environment is harsh selection acts strongly and individual differences in quality are amplified.

Question 18

It seems obvious that condition dependent traits are largely affected by environmental stress. True or false?

Answer 18

True.

Question 19

Give an example of an experiment used to assess the affect of environmental stress on condition dependent traits.

Answer 19

1. The environmental stress was larval food availibiltiy for stalk-eyed flies.
2. Compared the effect of this on a variety of non-sexual traits like female eye stalk size, male and female body size etc.
3. Male eye-stalk length suffered the most, showing condition dependent traits suffer in environmental stress.

Question 20

Another experiment was conducted with full and half-sib stalk-eyed fly families in 3 different environments. It was found that ‘genotypes that produced large ornaments in one environment did so in others as well, and stress magnified any differences between genotypes in terms of ornament expression’. Put simply what does this mean?

Answer 20

That large male eye stalks are a sign of genetic quality, as in harsh environments these individuals managed better than those with smaller eye stalks.