Animal behaviour: behavioural plasicity

Question 1

what is phenotypic plasticity?

Answer 1

phenotypic plasticity =
ability of an organism to ‘produce’ different phenotypes depending on environmental/ internal conditions.

e.g: Membranipora membranacea have inducible defenses. Zooids respond to grazing from nudibranch by expressing a spink phenotype this requires additional energy but allows them to defend and survive

It is a huge & wide ranging field.

Question 2

See: Pigliucci M. 2001: Phenotypic Plasticity – Beyond Nature and Nurture

Answer 2

following sections:
–The Genetics of Phenotypic Plasticity
–The Molecular Biology of Phenotypic Plasticity
–The Developmental Biology of Phenotypic Plasticity
–The Ecology of Phenotypic Plasticity
–Behavior and Phenotypic Plasticity
–Evolution of and by Phenotypic Plasticity
–The Theoretical Biology Phenotypic Plasticity
–Phenotypic Plasticity as a central concept in Evolutionary Biology

Question 3

the “mapping function” problem

Answer 3

*Genotype and Phenotype: The “Mapping Function” Problem (G->P)
*Long search for relationship between genes and phenotypes (Alberch 1991).

The simplest possible G->P mapping function:
–Single locus effects
–‘Mendelian’.

Most characters are not as straight-forward and are controlled by many genes:
–i.e. quantitative characters
–pleiotropy & epistasis.

genotype phenotype interactions increase in complexity according to gene interactions (see diagram in notes)

Figuring out a more realistic model of the G-> P is one of the major challenges in Biology, at all levels of biological organisation. There is potential to unify disciplines of evolutionary, ecological, behavioural, developmental, and molecular biology.

Question 4

The reaction norm approach

Answer 4

*Reaction norm: a function relating environments that a particular genotype is exposed to with the phenotypes that can be produced by that genotype

*Populations vs. individuals

*Characterized by their slope & intercept (elevation)

• These studies are often done at population level and calculated from pop averages

Often simplified (trait expression between two diff environmental conditions)

–In reality more complex shapes are probable;
–can still describe as mathematical functions

Constraints to plasticity – not possible for organisms to change constantly
So there is a limited range of values that a trait can express

Question 5

Reaction norm examples

Answer 5

antler size and proportion of male competitors e.g. deer
clutch size and relative resource abundance e.g. blue tit
aggressiveness and colony density e.g. seals

Question 6

Reaction norms have several fundamental properties

Answer 6

see diagram in notes
Difference between the degree (or amount) of plasticity, and the pattern of plasticity;
–All similar pattern (+ve), but slope directly quantifies the degree of plasticity.

Question 7

Reaction norms: issues : What constitutes the environment axis?

Answer 7

How to define environmental variables? They can be quite wide ranging

Abiotic or biotic

Continuous or discontinuous
- Temperature
- density
- + predator / – predator (= contexts?)

Time e.g. age, seasons.
i.e. : Broad ranging

Question 8

Behavioural plasticity

Answer 8

*Plasticity is not the same as behaviour –animals show both plasticity & behaviour
*Some behaviours are highly plastic (e.g. learning) and others less so (“innate”).
-> use the term ‘behavioural plasticity’ to differentiate it from behaviour
Some behaviours are more plastic than other

Question 9

Is behavioural plasticity different? (to other forms of plasticity)

Answer 9

Behaviour is one of the manifestations of phenotypic plasticity – just as development, morphology, physiology etc. are.

But has the potential to:
–develop via learning
–(similar to developmental plasticity)
–‘every-day’ behaviour is v. flexible and reversible on a v. short time scale (hours, mins, seconds),
–Typically possible throughout individual’s life span

-> Potential for rapid response to changes in environment

Question 10

Examples of developmental plasticity also show rapid response

Answer 10

Cf. morphological/developmental plasticity:

–usually irreversible (at least at the organ level)
–occurs over a longer time span.
–developmental plasticity depends on windows of availability

examples:
- darker Pontia butterfly morphs are able to absorb more sunlight for activity so darker morphs occur in early hatching butterflies
- if spadefoot tadpoles are born in wet conditions they develop omnivorously with large gut and small jaw foraging for pondweed and smaller life forms
if hatched in dry conditions they develop carnivorous nature with small gut and large jaw and cannibalise other tadpoles

Question 11

BUT…physiological plasticity can have very short time scales and reversibility (Piersma and Lindstrom,1997)

Answer 11

for example:
- distension of body following a kill e.g. snakes
- change in muscles for long flight e.g. migratory birds

Question 12

Behavioural plasticity is closely linked to physiological plasticity

Answer 12

;it requires flexibility in physiological ‘machinery’ to allow behavioural flexibility

Natural and sexual selection
Act on behavior

Morphology, physiology and biochemistry determine organisms performance ability
and thus constrain behaviour

Physiological systems also place constraints on degree of behavioural plasticity.

Question 13

Behavioural plasticity: costs and limits

Answer 13

*If no cost or limits to plasticity -> evolution of ‘Darwinian demons’!!
*This doesn’t happen so we know there are limitations
What limits the evolution of phenotypic plasticity?

Question 14

Costs of plasticity (De Witt et al. (1998))

Answer 14

*Production: excess cost of producing structures plastically (when compared to the same structures produced through fixed genetic responses)

*Maintenance: energetic costs of sensory and regulatory mechanisms

*Information acquisition: energy expenditures for sampling the environment, including energy/time not used for other activities (e.g., mating, foraging) - resulting in pro/reactive behaviour

*Developmental instability: plasticity may imply reduced canalization of development within each environment, or developmental “imprecision”

*Genetic: due to deleterious effects of plasticity genes through linkage, pleiotropy, or epistasis with other genes

Question 15

Limits of plasticity (De Witt et al. (1998))

Answer 15

Information reliability: the environmental cues may be unreliable or changing too rapidly

Lag time: the response may start too late compared to the time schedule of the environmental change, leading to maladaptive plasticity

Developmental range: plastic genotypes may not be able to express a range of phenotypes equivalent to that typical of a polytypic population of specialists

Epiphenotype problem: the plastic responses could have evolved very recently & function more like an “add-on” to the basic developmental machinery than an integrated unit; as such, its performance may be reduced – plastic traits build on existing traits

Question 16

Individual variation in plasticity

Answer 16

*Few studies of individual variation in plasticity

*Fewer on individual variation in behavioural plasticity

*or how selection acts on plasticity

Still a relatively new field of study

see individual reaction norms graphs in notes

Question 17

individual reaction norms example: Red deer maternal traits

Answer 17

Plasticity in red deer maternal traits study
(Nussey et al. 2005)

*changes in calving date in relation to autumn rainfall over a 30-yr study of 2147 red deer on the Isle of Rum.
*phase of low and rising population density
*phase of high & fluctuating population density
*Population-level trend of delayed calving dates following years of high autumn rainfall– explained by variation within individual females

*Phenotypic plasticity in a maternal trait in red deer in modifying calving date (Nussey et al 2005)
*Significant variation between females in average calving dates and in individual plastic responses of calving date to autumn rainfall.

*Females born in LOW population density phase were, on average, phenotypically plastic for the calving date-autumn rainfall relationship and showed significant variation in plasticity.
*Females born at HIGH population density - on average no significant plasticity for calving date, but variation in plastic responses was still present.

Selection favoured females with increasingly positive plastic responses of calving date to autumn rainfall.

reasoning:
*early experience of high population density -> poorer physiological condition,
*Life history effects – later in life

–females who suffered poor condition (‘HIGH’) are less able to make a physiological/behavioural response to change in environmental (i.e. less able to calve early following dry autumns)
–Except in a few high quality individuals (fitter, higher reproductive success)

*LOW density females – no such limitation – can ‘adjust’ to environment

Question 18

Can plasticity evolve?

Answer 18

*Theoretical and laboratory research suggests that phenotypic plasticity can evolve under selection.

*Variation between individuals in plasticity – therefore open to selection?
*Variation varies with environment too
*But, few studies in wild systems.

Environment may determine amount of variability and potential for adaptation

Question 19

Example of plasticity evolution: reproduction timing in Great tits

Answer 19

Timing of reproduction in great tits (Parus major) (Nussey et al. 2005)

*warm spring -> breed earlier (phenotypic plasticity),
–individual-level response to temperature.
–Individuals vary in reaction norms
*Elevation & slope (plasticity)

Evidence that degree of plasticity can evolve?
–Requires significant genetic variation in slope or elevation
–Data from 833 females between 1973-2004 – long period ideal

Estimates of residual & additive genetic variance (gray) and h2 (white):

*(A) laying date–spring temperature slope
*(B) laying date elevation (laying date in the average environment).

-> significant genetic variation for plasticity

*there is evidence that selection on plasticity is occurring.
–Relationship between LRS (fitness) and plasticity measure (slope)

(see graph in notes) higher neg. Means more plastic more able to adapt their laying date according to warmer spring

Initially more plastic individuals were doing worse than plastic, over time it becomes more beneficial to be plastic – overall however population decline is observed

*Also – evidence that selection on plasticity is increasing over time.

–Relationship between LRS (fitness) and plasticity measure (slope) changes over time

looking at different time periods shows how plasticity is becoming more advantageous – probably in relation to climate change

Question 20

Conclusions from timings of reproduction in Great Tits (Nussey 2005):

Answer 20

Heritable variation in individual plasticity

Wild population

Temporal trends in natural selection on heritable plasticity
- Selection favoring highly plastic individuals has intensified

Concurrent with changes in climate and the timing of food availability.
-> mismatch between the breeding times of the birds and food

Continued selection on plasticity can act to alleviate this mismatch.

Question 21

Relevance of behavioural plasticity

Answer 21

Ability to modify behaviour in own lifetime essential to adapt to environmental change may help to buffer slower acting plasticity such as physiological.

*Within-individual phenotypic plasticity represents one important means by which populations can track environmental changes.

*The other is microevolution: a change in genotypes across generations in response to selection on a trait.

^ Assessing the relative importance of these two processes is crucial to our understanding of the evolutionary and ecological dynamics of populations

*Relevance under rapid environmental change scenarios.

*Current long-term anthropogenically driven environmental change,

–Plasticity -> potential to determine ability of populations to respond adaptively to environmental variation

BUT….
–Need to understand how natural selection acts on plasticity under altered levels of environmental variation.

–At present little is known.

Question 22

Plasticity summary

Answer 22

*Plasticity in life history &/or behavioural traits is ubiquitous in animal populations, with traits often varying within the lifetimes of individuals depending on the conditions they experience .

*It is typically conceptualized & measured using reaction norms: linear functions describing the change in a trait across an environmental gradient.

*Laboratory & some field research has shown that genetic variation for plasticity exists and that heritable plasticity can respond to artificial selection.

*Detailed analyses of within-population variation in in naturally occurring populations are rare, because such analyses require data from large numbers of individuals breeding repeatedly across their lifetimes.

Question 23

Behavioural plasticity examples: lacewings

Answer 23

Chrysoperla (green lacewing) morphs
(Wells and Henry (1992))
Found 5 elements of courtship songs :
duration, interval, initial, middle & end frequency

consistent differences among the 3 morphs
may result in reproductive isolation & potential speciation

variation in song traits depends on temperature
(plasticity)
But pattern & degree Of plasticity varied between
morphs suggesting the possibility that variations originated as a plastic response to simple environmental factors
(temperature).

Thus this links plasticity, behaviour, reproductive morphology & macroevolution

Question 24

Behavioural plasticity examples: white crowned sparrow

Answer 24

nature vs nurture: song learning in birds
These sparrows were found to have local dialects in California (Marler and Tamura 1982)

Question 25

Behavioural plasticity example: Stoats

Answer 25

Females found to respond to the odour of a stoat (Ylonen and Ronkainen 1994)

Females actively avoid copulation under high predation risk - surpressing breeding behaviour

cf. males - complete lack of response