Phenotypic plasticity

Question 1

What is phenotypic plasticity?

Answer 1

The ability of a given genotype to express multiple phenotypes in response to environmental variation

Question 2

What is a genetic programme?

Answer 2

A system that transforms genotype into phenotype

Question 3

Can genetic programmes be modulated by the environment?

Answer 3

Yes

Question 4

Phenotypic plasticity shows that not only genetic variation can cause phenotypic diversity, but also…

Answer 4

environmental sensitivity

Question 5

Phenotypic plasticity be viewed as WHAT in unpredictable environments?

Answer 5

An adaptive strategy

Question 6

Give an example of an unpredictable environment.

Answer 6

One with seasonality

Question 7

Is phenotypic plasticity rare? Why, why not?

Answer 7

No; for many traits it is the default as developmental/physiological/metabolic processes are inherently sensitive to the environment

Question 8

Give 4 examples of some environmental variables that developmental/physiological/metabolic might be sensitive to.

Answer 8

Changes to temperature, pH, ion content and nutrient availability

Question 9

Sensitivity to the environment produces reactions norms. Define a reaction norm.

Answer 9

The range of phenotypes produced by a given genotype when exposed to a range of values of a single environmental value

Question 10

It has been discussed whether phenotypic plasticity can contribute to species diversification. Is there much evidence for this?

Answer 10

No; it is largely theoretical debate with few empirical examples

Question 11

Why might phenotypic plasticity impede diversification?

Answer 11

Because the variation in morph is non-genetic and thus non-heritable, meaning selection cannot act on it. This therefore implies there is no potential for evolutionary change through selection.

Question 12

Why might phenotypic plasticity facilitate diversification?

Answer 12

Different populations of a species are exposed to different environments and thus exhibit different phenotypes. Selection can then favour the constitutive expression of each phenotype in its particular environment.
Essentially as a particular phenotype is best-suited and so continuously expressed in a given environment, it will be favoured and eventually plasticity will be lost.

Called ‘RELEASE OF CRYPTIC VARIATION’

Question 13

Define constitutive expression.

Answer 13

When a gene is transcribed continually instead of facultatively when needed.

Question 14

Are genes commonly expressed facultatively under phenotypic plasticity?

Answer 14

Yes, this is what allows for plasticity

Question 15

What single factor affects whether phenotypic plasticity either impedes or facilitates diversification?

Answer 15

Level of genetic variation

Question 16

Can phenotypic plasticity be fixed if there is no genetic variation?

Answer 16

No; if there is no variation there is nothing for selection to act on, meaning plastic responses will not be fixed and diversification cannot occur.

Question 17

What can happen to phenotypic plasticity if genetic variation is too high?

Answer 17

Selection can create a loss of plasticity as the constitutive expression of one phenotype per environment is favoured, perhaps leading to diversification of that sub-population but also creating a loss of adaptive potential.

Question 18

Give an example of phenotypic plasticity facilitating diversification.

What did they do?

Answer 18

Pfennig and McGee, 2010:

Authors compared sister groups among diverse taxa, looking for pairs in which one group displayed phenotypic plasticity and one that did not.

Question 19

Pfennig and McGee, 2010:

Which groups did they find that matched this pattern?

Answer 19

5 groups:

Salmonid fish
Cichlid fish
Sunfish
Toads
Salamanders

Question 20

Pfennig and McGee, 2010:

Give an example in amphibians.

Answer 20

Salamanders, genus Ambystoma, contains some phenotypically plastic species.

Salamanders of the genus Dicamptodon were all non-plastic.

Question 21

Pfennig and McGee, 2010:

What was the common trend the authors observed?

What does this suggest.

Answer 21

Plastic taxa were species-rich and occupied diverse habitats.

Non-plastic taxa were species-poor and occupied fewer habitat types.

Phenotypic plasticity aids diversification and speciation.

Question 22

To summarise:

How does genetic variation affect phenotypic plasticity and diversification at a) low and b) high levels?

Answer 22

a) Low genetic diversity = nothing for selection to act on = n diversification
b) High genetic diversity = selection favours a particular phenotype and removes the others = removes plastic and future diversification ability

Basically too little and too much both impede diversification

Question 23

Give a referenced example of phenotypic plasticity releasing cryptic variation that leads to divergence.

What is this called?

Answer 23

Pfennig et al., 2002;

Spadefoot toad is S. bombifrons.
New Mexico spadefoot toad S. multiplicata.
Two morphs, detritus feeding and carnivorous that feeds on fairy shrimp.

In sympatry both become more specialised, S. bombifrons becomes more carnivorous and S. multiplicata more omnivorous.

Called character displacement; differences in regions where species coexist geographical become accentuated in regions where they co-occur