Week 5: Plasticity

Examples of how behaviour can affect population growth

Territorial species

• less likely to colonise new environment after translocation than non-territorial?

Tree- cavity nesters

• More affected by deforestation than ground nesters

What data is needed to help understand the link between ecology and evolution?

Long term data on

• behaviour

• reproduction

• survival

• population dynamics

How can personality be important for predator avoidance (success in reintroduction)

• Higher activity levels

• Less neophobic

• Higher exploratory behaviour

• species/ context dependent

When will behaviour affect populations?

If it influences

• dispersal

• immigration/ emigration

• survival

• recruitment

How can variation at the individual level leave a mark at the population level?

• different levels of selection

• fitness-affecting behaviours

• births and deaths

• population

Why is behaviour a difficult trait to measure/ understand?

• Lack theory/ data

• Acts directly at the individual level, not the evolutionary level (population)

• Is more plastic than any other trait

• Changes at faster rate than other traits

• Has a richer set of evolutionary trajectories than other traits

Describing how the average value of a trait in a population changes from one generation to the next

Price Equation

What does the price equation account for?

Basic requirements of natural selection:

• Trait variation (z)

• Associated differences in fitness (w)

• Heritability (or transmission of a trait; change in trait value in parent to offspring (Δz))

Limitations of the Price Equation

• Limited to between-generations - doesn’t take account of behavioural plasticity explicitly (within generations)

• Doesn’t explain behaviour when most of the variation is environmental rather than genetic

Components of intra-generational change

• Viability selection

• Individual selection

Components of Inter-generational change

• Fertility selection

• Parent-offspring differences

Viability selection:

Does the trait improve survival of that individual within a season/generation?

• Covariance between survival (s) and the trait (z)

• For individual i

• Predation/ Disease/ Resources

Individual change:

How is the trait expected to change between time steps (e.g. early to late season) within the individual?

• Mean change in trait (Δz) within generation (i)

• Due to transmission of the trait (E)

• Weighted by survival (s)

• Individual plasticity/ Ontogeny/ Individual Learning

i.e. How plasticity in trait z tracks the environment

Fertility selection:

Does the trait improve reproduction of the surviving individual?

• Covariance between reproduction of surviving individuals (r) and the trait (z)

• For individual i

• Mate choice/ Contest/ Resources

Parent-offspring differences:

How is the trait expected to change between parent and offspring (i.e. across generations)?

• Mean change in trait (Δz) between generations i and j

• Due to transmission of the trait (E)

• Weighted by reproduction (r)

• Genetics/ Developmental plasticity/ Maternal effects/ Cohort effects

Why is individual change and parent-offspring differences particularly important to quantify adaptive/ maladaptive behavioural responses?

Related to learning, imprinting, cultural transmission (of information)

Types of Changes in the Anthropocene

• Habitat loss/ fragmentation

• Spread of invasive species

• Over-exploitation

• Pollution

• Climate Change

Possible consequences to changes in the Anthropocene

• Species decline

• Extinctions

• Range shifts

• Alters species interactions

• Evolutionary changes

• Adaptive evolutionary responses

• Speciation

• Hybridization

What is phenotypic plasticity?

Ability of a single genotype to alter its phenotype in response to environmental conditions

Why is phenotypic plasticity significant for the Anthropocene?

most important mechanism in accommodating response to anthropogenic change, not immediate genetic evolution

How can we visualise plastic phenotypic variation?

Reaction norms

Reaction norms

• Describes how a trait varies in response to an environmental signal

• Continuous phenotypic plasticity

• trait (y-axis); environment (x-axis)

Genetic variation may influence:

• Line slope (how trait changes with environment)

• Line elevation (trait value)

Two types of plasticity

• Developmental plasticity (incl. morphological

• Behavioural Plasticity (incl. physiological)

Example of developmental plasticity in phenotype

Polyphenisms

• Physical morphs determined during development in response to environmental signal

Example of developmental plasticity leading to behavioural diversity

• Horn size polyphenisms in male beetles Onthophagus Taurus

• Large horns → males defend/ guard

• Small horn → males sneak

How can developmental plasticity be regulated?

Transcriptomic regulation (via gene expression)

Mechanisms of Phenotypic Plasticity

• Genetic assimilation

• Genetic accommodation

Genetic accommodation

initially environmentally induced phenotype (plastic response) becomes genetically fixed or modified over generations through natural selection, acting on underlying genetic variation.

Genetic Assimilation

• a phenotype (a trait) initially induced by an environmental stress becomes genetically fixed

• loss of plasticity

Plasticity and the Anthropocene

• Human influence is driving phenotypic change in wild animal populations

• Rates of phenotypic changes are greater in anthropogenic than natural contexts

• Sometimes genetic basis, but phenotypic plasticity is especially impt.

• Changes in plasticity can be very abrupt