Transcript Evolution and adaptation

Evolution and Adaptation
- mutation
- migration
- genetic drift
- Natural Selection
Darwin’s Postulates:
(1) There is heritable variation
(2) There is a struggle for existence
(3) Variation influences the struggle
and Natural Selection follows ...
(1) There is heritable variation
Heritability in selected human traits:
Handedness
Diastolic blood pressure
Twinning
Systolic blood pressure
Body weight
Stature and tooth size
30%
45%
50%
55%
65%
85%
Fertility
IQ
10-20%
60-80%
(2) There is a struggle for existence
Resources are limiting
There is competition for resources, including mates
(3) Variation influences the struggle
Columbian ground squirrel
dicots
vs..
monocots
Monocots consumed
Digestive
constraint
Optimal diet
time
constraint
Dicots consumed
min energy
constraint
Mixture of monocots and dicots
- Monocots limited by handling time
- Dicots limited by digestion
Mark Ritchie compare the predicted “optimal” diet and the
actual diet for 109 individuals squirrels
Monocots consumed
(a) variation in the ability
to forage optimally
r2 = 0.94
Dicots consumed
Mark Ritchie compare the predicted “optimal” diet and the
actual diet for 109 individuals squirrels
Monocots consumed
(a) variation in the ability
to forage optimally
r2 = 0.94
Optimal
Deviators
Dicots consumed
Offspring’s deviation
(b) optimal foraging is a heritable trait
Mothers raise offspring
Offspring on their own
Mother’s deviation
(c) There is a struggle for existence
Relative to optimal foragers, deviators have lower surplus
energy intake and ....
(c) Variation influences the struggle
... as a consequence, deviators have
i) lower somatic growth
ii) lower survival
iii) smaller litter sizes
Mark Ritchie’s study beautifully illustrates Darwin's Postulates in action:
Heritable Variation
Struggle for Existence
Variation influences the Struggle
but...falls short of documenting Natural Selection
Evolution by Natural Selection – Guppies on the island of Trinidad
Evolution by Natural Selection – Guppies on the island of Trinidad
Life history traits
Schooling behavior
- dilutes individual risk
- greater vigilance
- group confusion
low
risk
Predator-inspection behavior
- method to ascertain the identity
and intentions of the assailant
low
risk
(Magurran et al. 1996)
(Endler 1980)
Male coloration and female choice
mean # spots
mean size
Predation risk
(cichlids)
Low risk
Predation risk
(prawns)
Correlations vs. experimental tests
Haskin’s 1957 transplant experiment
Transplant experiment results:
black = % females schooling
10mm
(Magurran et al. 1996)
Summary:
1) “Natural experiment” – Guppy populations that have experienced different
regimes of predation risk show different levels of anti-predator behavior
2) Transplanted (1957) high-risk guppies behave like native low-risk guppies
(evolution in 34 years or ~100 generation)
3) Changes in color-patterns that function in mate choice were apparent after
13 months!!
At what level does Natural Selection operate?
The Individual or the Group?
“lions rarely fight to the death because if they did it would
endanger the survival of the species”
“salmon migrate thousands of miles from the ocean to their inland spawning grounds
killing themselves in the process with exhaustion to ensure the survival of the species”
Wynne-Edwards proposed that organisms have adaptations to ensure its population
or species controls its rate of consumption Likewise, individuals should restrict their birth
rate to prevent over-population
Are these accurate statements??
“lions rarely fight to the death because if they did it would
endanger the survival of the species”
“salmon migrate thousands of miles from the ocean to their inland spawning grounds
killing themselves in the process with exhaustion to ensure the survival of the species”
Wynne-Edwards proposed that organisms have adaptations to ensure its population
or species controls its rate of consumption Likewise, individuals should restrict their birth
rate to prevent over-population
Are these accurate statements??
NO!
Natural selection acts at the level of the individual, not the group
Group Selection – differential survival/reproduction of groups
C
C
C
S
C
C
S
C
S
C CC
C S
C C
C
X
C
S
S
S C
S
C CC
C S
C C
C
S
X
S S
But why won’t
this work?
1) Groups would have to die out faster than individuals, which rarely
happens
2) Groups would have to be isolated
3) “Cooperative” groups are always vulnerable to invasion of
selfish individuals
This does not mean cooperation or behaviors that serve the “good
of the group” cannot evolve (reality tells us differently), but
rather that most of these behaviors are inherently selfish
The “selfish” individual reaps the rewards in a world of self-restraint
It receives a private benefit while everyone shares the public cost
Aka. Trajedy of the Commons
Introduction to:
alternative mating strategies
sexual selection and mate choice
reproductive behavior and the roles of males and females
foraging behavior
anti-predator behavior
living in groups
cooperation
social contracts
Formulating and testing hypotheses about the evolution of behavior:
(1) Experimental approaches – particularly those that
make quantitative rather than qualitative predictions
(2) The comparative approach – when experiments fail...