EE LEC 1 - PHENOTYPIC PLASTICITY

What is phenotypic plasticity?

The ability for a single genotype to produce different phenotypes when exposed to different environments

How do individuals respond to environmental change?

• Behaviour

• Physiology

• Life-history

How do populations respond to environmental change?

• Behaviour

• Performance

• Physiology

PP involves complex traits - what are they?

• Common at high levels of biological organisation

• Made of many subordinate traits

• Capable of exhibiting emergent properties

• Often modular

• Affected by many genes and environmental factors

What are emergent properties?

Properties that become apparent and result from various interacting components within a system but are properties that do not belong to the individual components themselves

What is modularity?

Organisation of biological systems into discrete, self-contained units that perform specific functions

2 examples of complex traits in humans:

• Brain

• Eye

What is the selection hierarchy?

Refers to the idea that natural selection can act at different levels of biological organization, from genes to species and beyond

What are reaction norms?

The spectrum of phenotypic variation produced when individuals of the same genotype are exposed to varying environmental conditions

Genotype - individual level

The actual set of genes affecting the phenotype and shaping all aspects of the norm of reaction

Plasticity - individual level

An attribute of the individual reaction norm, indicating that the genotype generates different phenotypes depending on the external conditions

Genotype x Environment - individual level

The idea that genotypes and environments interact mechanistically throughout the development of an organism to produce its phenotype

What are the costs of plasticity?

Results in a decrease in fitness even when an optimal phenotype is expressed

What are the limits/constraints of plasticity?

Exist in the failure to express an optimal phenotype to begin with

What is the phenotypic plasticity cascade?

1. Something in the internal andor/external envrionment changes

2. Organism senses that change

3. Organism alters gene expression

4. Usually, the altered gene expression yields additional observable phenotypes

Phenotypic plasticity cascade - step 1

Changes in ambient temperature, humidity or oxygen concentration would constitute external environmental factors.

Phenotypic plasticity cascade - step 2

Some changes may occur without any formal sensing by the organism, e.g. as result of direct effects of temperature on the rates of ongoing physiological processes

Phenotypic plasticity cascade - step 3

Some plastic responses need to involve changes in gene expression but instead could occur via phosphorylation of existing proteins, changes in protein levels caused by variation in protein ubiquitination, or simulation of existing microRNAs

Phenotypic plasticity cascade - step 4

If changes occur at lower levels, higher-level traits might show no apparent change

Hierarchical masking effect

Compensatory plasticity at lower levels could lead to reduced plasticity at higher levels

What are the characteristics of PP?

• Changes may or may not be reversible

• Changes may or may not be adaptive

• Behavioural plasticity (compensation) might shield lower-level traits from selection

• At population level, phenotypic plasticity in behaviour and other traits can facilitate invasions of new habitats

When is non-adaptive plasticity expected?

When an organism is exposed to environmental conditions with which it is unfamiliar in terms of its evolutionary history

When should phenotyic plasticity evolve?

Intuitively:

• Not in a constant environment

• Not if variation in environmental factors are entirely unpredictable

Stress

Anything that threatens homeostasis, survival or other components of Darwinian fitness

Reversible phenotypic plasticity would be expected for all organisms if…

• They are exposed to stress periods that last shorter than life span

• Stress appears in the long run with some regularity so that natural selection can shape plastic traits

How to study evolution (PP)

• Reciprocal transplant experiments

• Common garden experiments

What is a reciprocal transplant experiment?

Ecological studies where organisms from different envrionments are moved to the other’s habitat, allowing researchers to compare the relative fitness of populations in their native versus alternative environment

What is a common garden experiment?

A research method where organisms from different populations or environments are raised together in a controlled, standardized environment to assess the influence of genetics and the environment on traits