Evolution and Adaptation

1
Evolution and Adaptation

• mutation
• migration
• genetic drift
• Natural Selection

2

• Darwins Postulates
• There is heritable variation
• There is a struggle for existence
• Variation influences the struggle

and Natural Selection follows ...
3
(1) There is heritable variation
4
Heritability in selected human traits
Handedness 30 Diastolic blood
pressure 45 Twinning 50 Systolic blood
pressure 55 Body weight 65 Stature and tooth
size 85 Fertility 10-20 IQ 60-80
5
(2) There is a struggle for existence
Resources are limiting There is competition for
resources, including mates
6
(3) Variation influences the struggle
dicots
vs..
Columbian ground squirrel
monocots
7
Monocots consumed
time constraint
Dicots consumed
Mixture of monocots and dicots - Monocots limited
by handling time - Dicots limited by digestion
min energy constraint
8
Mark Ritchie compare the predicted optimal diet
and the actual diet for 109 individuals squirrels

• variation in the ability
• to forage optimally

r2 0.94
Monocots consumed
Dicots consumed
9
(b) optimal foraging is a heritable trait
Mothers raise offspring
Offsprings deviation
Offspring on their own
Mothers deviation
10
(c) There is a struggle for existence
Relative to optimal foragers, deviators have
lower surplus energy intake and ....
11
(c) Variation influences the struggle
... as a consequence, deviators have i) lower
somatic growth ii) lower survival iii) smaller
litter sizes
12
Mark Ritchies study beautifully illustrates
Darwin's Postulates in action Heritable
Variation Struggle for Existence Variation
influences the Struggle but...falls short of
documenting Natural Selection
13
Evolution by Natural Selection Guppies on the
island of Trinidad
Life history traits
14

• Schooling behavior
• dilutes individual risk
• greater vigilance
• group confusion

• Predator-inspection behavior
• method to ascertain the identity
• and intentions of the assailant

low risk
low risk
(Magurran et al. 1996)
15
(Endler 1980)
Male coloration and female choice
Start of exp
w/o
mean spots
w/predators
mean size
Months
Predation risk (prawns)
Predation risk (cichlids)
Low risk
16
Correlations vs. experimental tests Haskins 1957
transplant experiment
17
Transplant experiment results
(Magurran et al. 1996)
18
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!!
19
At what level does Natural Selection operate?
The Individual or the Group?
20
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??
The selfish individual reaps the rewards in a
world of self-restraint Public cost versus
private benefit
not material rewards, but passing on more copies
of its selfish strategy
21
Group Selection differential survival/reproducti
on of groups
C
C
C
C
S
C
C
C
C
C
S
C
C
C
C
C
C
S
C
C
C
C
S
X
C
C
S
S
S
X
C
S
S
S
S
S
But why wont this work?
22

• 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

23
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 Public cost versus
private benefit
Punish defectors ....
24
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
25
Formulating and testing hypotheses about the
evolution of behavior

• Experimental approaches particularly those that
  
• make quantitative rather than qualitative
  predictions
• (2) The comparative approach when experiments
  fail...

26
Sociality in Weavers a comparative approach

• Observations
• 90 species of roughly similar looking species
  found throughout Africa and Asia
• Some are solitary and some travel in large
  flocks
• Some build cryptic nests in large defended
  territories while others cluster nests
• together in colonies
• Some are monogamous with a permanent pair bond
  between males and females
• while other are polygamous with the males
  contributing little care of the offspring
• How can we explain this great
  diversity of behavior?

27
John Crook (1968) applied the comparative
method by searching for correlations between
aspects of social organization and species
ecology food type food distribution and
abundance predators nest sites
28
Weavers fell into 2 broad categories
Baya Weaver build cryptic, solitary nests in
the forest, feed alone for insects in large
territories, monogamous with males resembling
females
29
Masked Weaver Savannah species, seed-eaters,
feed in large flocks, nest colonially in bulky
cryptic nests, build cryptic, polygamous with
strong sexual dimorphisms females dull, males
brightly colored
30
Why is the relationship of behavior/morphology
link to their ecology?

• Forest
• food is dispersed - birds feed solitarily at
  defended resource patches
• food is dispersed both males and females
  required to feed young
• both parents tend young dull coloration to
  avoid attracting predators
• dispersed cryptic nests avoid detection by
  predators

• Savannah
• seeds patchy but locally abundant foraging in
  groups facilities searching success
• nests cannot be hidden in the open country
  seek safety in sheltered sites
• sheltered sites are rare and scattered colonial
  nesting
• males can now defend access to the best nesting
  sites
• likewise, abundant food emancipates the male
  from parental cares spends time
• attracting mates evolution of polygamy and
  showing plumage to advertise