Phenotypic plasticity Flashcards
What is phenotypic plasticity?
The ability of a given genotype to express multiple phenotypes in response to environmental variation
What is a genetic programme?
A system that transforms genotype into phenotype
Can genetic programmes be modulated by the environment?
Yes
Phenotypic plasticity shows that not only genetic variation can cause phenotypic diversity, but also…
environmental sensitivity
Phenotypic plasticity be viewed as WHAT in unpredictable environments?
An adaptive strategy
Give an example of an unpredictable environment.
One with seasonality
Is phenotypic plasticity rare? Why, why not?
No; for many traits it is the default as developmental/physiological/metabolic processes are inherently sensitive to the environment
Give 4 examples of some environmental variables that developmental/physiological/metabolic might be sensitive to.
Changes to temperature, pH, ion content and nutrient availability
Sensitivity to the environment produces reactions norms. Define a reaction norm.
The range of phenotypes produced by a given genotype when exposed to a range of values of a single environmental value
It has been discussed whether phenotypic plasticity can contribute to species diversification. Is there much evidence for this?
No; it is largely theoretical debate with few empirical examples
Why might phenotypic plasticity impede diversification?
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.
Why might phenotypic plasticity facilitate diversification?
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’
Define constitutive expression.
When a gene is transcribed continually instead of facultatively when needed.
Are genes commonly expressed facultatively under phenotypic plasticity?
Yes, this is what allows for plasticity
What single factor affects whether phenotypic plasticity either impedes or facilitates diversification?
Level of genetic variation
Can phenotypic plasticity be fixed if there is no genetic variation?
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.
What can happen to phenotypic plasticity if genetic variation is too high?
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.
Give an example of phenotypic plasticity facilitating diversification.
What did they do?
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.
Pfennig and McGee, 2010:
Which groups did they find that matched this pattern?
5 groups:
Salmonid fish Cichlid fish Sunfish Toads Salamanders
Pfennig and McGee, 2010:
Give an example in amphibians.
Salamanders, genus Ambystoma, contains some phenotypically plastic species.
Salamanders of the genus Dicamptodon were all non-plastic.
Pfennig and McGee, 2010:
What was the common trend the authors observed?
What does this suggest.
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.
To summarise:
How does genetic variation affect phenotypic plasticity and diversification at a) low and b) high levels?
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
Give a referenced example of phenotypic plasticity releasing cryptic variation that leads to divergence.
What is this called?
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
