BioE 109
Lecture 14
Adaptation
Adaptation
What is adaptation?
-
the term “adaptation” has different meanings in different
fields of biology.
1.  physiologists use adaptation to describe acclimatization.
-  acclimatization refers to the physiological adjustment of
individual organisms to different conditions (e.g.,
temperature, photoperiod).
-
note that there is no genetic change.
2. to evolutionary biologists, adaptation is used in two
different ways.
Adaptation
1. the process of becoming adapted.
- the first definition of adaptation is as a process, i.e., the process
of becoming adapted.
- according to this definition, adaptation occurs by the process of
natural selection that we considered in class.
- for the process of adaptation to occur there must exist genetic
variation among individuals in the population and among these
different genotypes there must exist differences in relative fitness
to drive the selective process.
- according to this definition, adaptation is synonymous with the
process of natural selection.
Adaptation
2. the state of being adapted.
- the second definition of adaptation is perhaps more widely used.
- it refers to the end-point of this process, i.e., the state of being
adapted.
- according to this definition, adaptation is the end product of the
process of natural selection.
- individual characters of organisms are viewed as adaptations.
- what is the common feature of all these traits?
- the answer is that all are assumed to have evolved by the
process of natural selection.
- unlike the previous definition, however, we cannot observe this
process directly but must infer its past action.
Adaptation
How do we recognize adaptations?
Adaptations have two characteristics:
1.  complexity
- complexity can only evolve by natural selection.
- many examples exist of traits being suspected of being
adaptations prior to any evidence based on the criteria of
complexity.
- for example, the histological complexity of the lateral line in
fishes and its uniformity in many clades suggested to
physiologists that it was an adaptation.
- this was eventually confirmed after extensive study showed
that it proved to be sensitive to differences in water
pressure.
Complexity
Complexity
Adaptation
2. appearance of design
- often we can infer the function of a structure from design principles that an
engineer might apply to accomplish some goal like locomotion or the
retention or dissipation of heat.
- for example, in hot environments plants with large leaves often have leaflets
or lobed forms that help to reduce the leaf’s temperature.
- in many species of birds and mammals, those in colder environments tend to
have larger bodies (Bergman’s rule) and have shorter ears and legs (Allen’s
rule).
- both factors tend to reduce the rate of body heat loss by acting to decrease
the ratio of surface area to body mass.
- these characteristics have the appearance of “design”- i.e., that they have
been constructed or arranged to accomplish some function like growth,
defense or dispersal.
- in the non-living world we see nothing comparable to “complexity” or
“design”.
Spider silk
The adaptationist program
1.  Observe or describe some organism trait.
2. Formulate an adaptive hypothesis for the
evolution of that trait.
3. Test hypothesis by experiment or by collecting
additional data.
Examples
Batesian mimicry
Muellerian mimicry
Batesian mimicry (1861)
Batesian mimicry involves a palatable, unprotected species (the mimic) that closely resembles an unpalatable or protected species (the model)
Henry Walter Bates 1825-1892
Monarch Butterfly
Viceroy Butterfly
Blue Jay
Muellerian mimicry (1890)
Muellerian (Mullerian) mimicry
refers to two unpalatable species that are mimics
of each other with conspicuous warning coloration
(also known as aposematic coloration).
Fritz Mueller 1821-1897
Muellerian mimicry
Two or more unpalatable species look like each other
Two wasps species, both with stingers
Muellerian mimicry
Two or more unpalatable species look like each other
Heliconius butterflies, all bad tasting
Pitfalls
-  Giraffes
- Polar Bears
The neck of the Giraffe
The neck of the Giraffe
Foraging-competition hypothesis
The neck of the Giraffe
Most feeding is done below neck height.
7
7
Feeding height (meters)
6
6
5
Males
4
4
3
3
2
2
1
1
0
0
0
20
40
Females
5
0
20
Percentage of feeding bites
40
The neck of the Giraffe
Male-male competition
“Simmons and Schemers (1996)”
Fighting
Gerenuks
(Giraffe necks)
Leaf insects
The common cuttlefish (Sepia officinalis)
Cuttlefish crypsis
Cuttlefish crypsis
How do we study adaptations?
How do we study adaptations?
1. The experimental approach
How do we study adaptations?
1. The experimental approach
• hypotheses for the adaptive origins of traits are tested by
experiments.
How do we study adaptations?
1. The experimental approach
• hypotheses for the adaptive origins of traits are tested by
experiments.
2. The comparative approach
How do we study adaptations?
1. The experimental approach
• hypotheses for the adaptive origins of traits are tested by
experiments.
2. The comparative approach
• hypotheses for the adaptive origins or traits are tested
by:
How do we study adaptations?
1. The experimental approach
• hypotheses for the adaptive origins of traits are tested by
experiments.
2. The comparative approach
• hypotheses for the adaptive origins or traits are tested
by:
(a) Performing comparisons among species
How do we study adaptations?
1. The experimental approach
• hypotheses for the adaptive origins of traits are tested by
experiments.
2. The comparative approach
• hypotheses for the adaptive origins or traits are tested
by:
(a) Performing comparisons among species
(b) Making observations within species
The experimental approach
Example: the tephritid fly, Zonosemata vittigera
The experimental approach
Example: the tephritid fly, Zonosemata vittigera
Initial observations:
The experimental approach
Example: the tephritid fly, Zonosemata vittigera
Initial observations:
1. distinctive dark wing bands
The experimental approach
Example: the tephritid fly, Zonosemata vittigera
Initial observations:
1. distinctive dark wing bands
2. wing-waving behavior
The experimental approach
Example: the tephritid fly, Zonosemata vittigera
Initial observations:
1. distinctive dark wing bands
2. wing-waving behavior
Initial hypothesis:
• markings and behavior mimics jumping spiders thus
deterring other predators.
The experimental approach
Example: the tephritid fly, Zonosemata vittigera
Initial observations:
1. distinctive dark wing bands
2. wing-waving behavior
Initial hypothesis:
• markings and behavior mimics jumping spiders thus
deterring other predators.
Alternative hypothesis:
• markings and behavior mimics jumping spiders to deter
predation by jumping spiders.
Staring down your enemy…
The experimental approach
Question:
The experimental approach
Question:
Do the traits actually mimic the threat display of the
jumping spider thereby allowing the fly to escape
predation?
The experimental approach
Question:
Do the traits actually mimic the threat display of the
jumping spider thereby allowing the fly to escape
predation?
Hypotheses:
The experimental approach
Question:
Do the traits actually mimic the threat display of the
jumping spider thereby allowing the fly to escape
predation?
Hypotheses:
HO: Flies do not mimic jumping spiders (null hypothesis).
The experimental approach
Question:
Do the traits actually mimic the threat display of the
jumping spider thereby allowing the fly to escape
predation?
Hypotheses:
HO: Flies do not mimic jumping spiders (null hypothesis).
H1: Flies mimic jumping spiders to avoid other predators.
The experimental approach
Question:
Do the traits actually mimic the threat display of the
jumping spider thereby allowing the fly to escape
predation?
Hypotheses:
HO: Flies do not mimic jumping spiders (null hypothesis).
H1: Flies mimic jumping spiders to avoid other predators.
H2: Flies mimic jumping spiders to avoid predation by
jumping spiders.
The experimental design
Experimental results
The comparative approach
(a) Performing comparisons among species
The comparative approach: testes size
in fruit bats & flying foxes
The comparative approach
(a) Performing comparisons among species
Observation: Testes size is highly variable among
species.
The comparative approach
(a) Performing comparisons among species
Observation: Testes size is highly variable among
species.
Hypothesis: Males have evolved large testes in some
taxa due to sperm competition.
The comparative approach
(a) Performing comparisons among species
Observation: Testes size is highly variable among
species.
Hypothesis: Males have evolved large testes in some
taxa due to sperm competition.
Prediction: A positive relationship should exist between
testes size and social group size.
The comparative approach
(a) Performing comparisons among species
Observation: Testes size is highly variable among
species.
Hypothesis: Males have evolved large testes in some
taxa due to sperm competition.
Prediction: A positive relationship should exist between
testes size and social group size.
(Assuming that sperm competition is more intense in
larger social groups.)
Relationship between testes size and social
group size
A potential problem – lack of independence
Performing phylogenetically independent
contrasts
After correcting for the phylogeny…
After correcting for the phylogeny…
YES!
Polar Bears
“Sterling 1974”
1 “sneak and pounce”
Polar Bears
54 “jump and crush”
233 “sit and wait”
Polar Bears
UV Hypothesis