Transcript Chapter 2 Foundations

Fundamental
Concepts in
Behavioural Ecology
The scope of Behavioural
Ecology
• The relationship between
behaviour, ecology, and
evolution
– Behaviour : The decisive
processes by which individuals
adjust their state and situation
according to variation in their
environment
• The value of a trait is determined
by how it affects fitness relative to
others in the population
The hypothetico-deductive
approach
• Competing hypotheses
– Falsifiable
• Predictions of the
hypothesis
• Tests of predictions
– Situations in which the
alternatives make different
predictions
– Falsification or corroboration
Evolutionary definitions
• Evolution: Change in gene frequencies over time
– A population-level process
• Genotype: The allelic composition of an individual
with respect to the locus(i) of interest
• Phenotype: The organism’s overall characteristics,
or a subset of those characteristics
• Genome: All of the genetic information carried by
an individual
• Environment: Everything external to the organism
A gene-centric view
• Genetic information is the
target of selection
– Organisms are vehicles for
genes
• Genomes are mortal, genes
are potentially immortal
• BUT, the fate of a given gene
is affected by its degree of
‘cooperation’ with other genes
Analyzing selection
1. Compare traits with
proxies of selection
•
•
Relative reproduction
Relative survival
2. Response to
selection
•
Change in allelic
frequencies
What controls the
phenotype?
• What does it mean that a trait is
“genetically” or “environmentally”
controlled?
–DNA in a dish
• The “genetic”
basis of fixed
traits
http://discovermagazine.com/2007/mar/eye-color-explained/eyes-400.jpg
Origin of phenotypic
variance
• Thinking about variance
• VP = V G + V E + V G X E
• VG = VAG + VD + VI
–VI = Epistatic effects
–VD = Dominance interactions
–VAG = additive genetic variance
• The only heritable kind
Heritability
• Heritability = h2 = VAG / VP
– The portion of the differences between
individuals that is transmitted to
descendants
– A measure of a
population’s ability
to respond to
selection
– Measures
resemblance among
relatives vs. non-relatives
Measuring heritability I
• Artificial selection
– Drawing time
• Strength of selection
= S = Pbar – Xbar
• h2 = R / S
• Estimates vary by
generation
Ritchie et al. 1996 Anim. Behav. 52:603-
Measuring heritability II
• Parent-offspring
regression
120
Offspring Aggression
– Compare traits
between parents
and offspring
– Assign mates
randomly
– Slope of best fit line
is observed
heritability
140
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Mean Parental Aggression
Interpreting heritability
• Heritability estimates vary by
population
–Varying levels of VA
• Heritability estimates vary by
environment
–VE contributes to VP
Phenotypic plasticity
• Phenotypic plasticity
is the capacity to
produce different
phenotypes according
to variation in the
environment
– It can be adaptive or
non-adaptive
http://weblog.ceicher.com/archives/tanlines.jpg
• VE is a measure of
expressed phenotypic
plasticity
• Norms of reaction
– Drawing time
http://wfsc.tamu.edu/faculty/tdewitt/webpage.htm
Fitness
• When to measure?
• Genotypic fitness
– Relative success of one
allele (or a set of alleles)
across two generations
• Individual fitness
– Relative ability of a
phenotype to produce
mature descendants
http://reneeashleybaker.files.wordpress.co
m/2007/12/richard-sandrak-aka-littlehercules.jpg
Evolution, selection, drift
• Selection pressure without evolution?
– Evolution requires heritable variation
• Evolution without natural selection?
– Mutation
– Genetic drift
• Importance depends on pop size
• Does not produce adaptation
– Random events
Adaptation
• Def 1: A trait that was fixed or
stabilized by selection because of its
effects on the inclusive fitness of its
bearer in ancestral environments
• Def 2: The process by
which a population
evolves to be better
suited to its
environment
Adapting to the
environment
• Four mechanisms
–Darwinian mutation
& selection
–Phenotypic
plasticity
–Cultural adaptation
–Niche construction
http://biologybk.st-and.ac.uk/cultures3/pix/deWfig1.jpg
http://home.earthlink.net/~gastropod/bvrdm.JPG
Inclusive fitness
• A simplified definition:
– “The sum of the direct and indirect fitness
effects of an individual's behaviors, where
the direct fitness effect is the impact on the
individual's fitness, and the indirect fitness
effect is the impact on the fitness of its
social partners, weighted by the degree of
relatedness between the individual and its
social partners.” (Ricklefs & Miller, 2001)
Recognizing genetic
similarity
• The green beard
• Subtler indicators of
genetic similarity
– Kinship
• Kin selection: Natural
selection for altruistic
behavior directed
toward kin
Hamilton’s rule
• An actor & a recipient
• Altruistic behavior will benefit the
actor’s inclusive fitness when …
• br – c > 0
– b = benefit to recipient
– c = cost to actor
– r = relatedness of actor and recipient