Transcript (Part 2) The adaptationist program

BIOE 109
Summer 2009
Lecture 8- Part I
Adaptation
What is adaptation?
http://www.naturefootage.com/video_clips/BF09_136
What is adaptation?
1. Acclimatization
What is adaptation?
1. Acclimatization
• refers to the physiological adjustment of individual
organisms to different conditions (e.g., temperature,
photoperiod). NO genetic change.
What is adaptation?
1. Acclimatization
• refers to the physiological adjustment of individual
organisms to different conditions (e.g., temperature,
photoperiod). NO genetic change.
What is adaptation?
1. Acclimatization
• refers to the physiological adjustment of individual
organisms to different conditions (e.g., temperature,
photoperiod). NO genetic change.
2. Adaptation
What is adaptation?
1. Acclimatization
• refers to the physiological adjustment of individual
organisms to different conditions (e.g., temperature,
photoperiod). NO genetic change.
2. Adaptation
• a trait that allows an individual to leave more
offspring than it would if it lacked that trait
What is adaptation?
1. Acclimatization
• refers to the physiological adjustment of individual
organisms to different conditions (e.g., temperature,
photoperiod). NO genetic change.
2. Adaptation
• a trait that allows an individual to leave more
offspring than it would if it lacked that trait
-Adaptations can be structural, behavioral or
physiological.
Camouflage
The common cuttlefish (Sepia officinalis)
Cuttlefish crypsis
Feeding
Defenses
How do we study adaptations?
There are three steps in carrying out the so-called
“adaptationist program”:
1. Observe or describe some organismal trait.
2. Formulate an adaptive hypothesis for the
evolution of that trait.
3. Test hypothesis by experiment or by collecting
additional data.
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 observational approach
How do we study adaptations?
1. The experimental approach
• hypotheses for the adaptive origins of traits are tested by
experiments.
2. The observational approach
• hypotheses for the adaptive origins or traits are tested by
making observations within species
How do we study adaptations?
1. The experimental approach
• hypotheses for the adaptive origins of traits are tested by
experiments.
2. The observational approach
• hypotheses for the adaptive origins or traits are tested by
making observations within species
3. 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 observational approach
• hypotheses for the adaptive origins or traits are tested by
making observations within species
3. The comparative approach
• hypotheses for the adaptive origins or traits are tested by
performing comparisons among species
The experimental approach
Staring down your enemy…
Example: the tephritid fly, Zonosemata vittigera
http://www.youtube.com/watch?v=bjUlPJk6rsU
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.
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 observational approach
Making observations within species
The observational approach
Making observations within species
The observational approach
Making observations within species – the polar
bear
Observation: Polar bears are white!
The observational approach
Making observations within species – the polar
bear
Observation: Polar bears are white!
Hypothesis: Polar bears evolved a white coat as an
adaptation to hunting in a white environment
The observational approach
Making observations within species – the polar
bear
Observation: Polar bears are white!
Hypothesis: Polar bears evolved a white coat as an
adaptation to hunting in a white environment
Prediction: Polar bears should hunt in a manner that
takes advantage of this camouflage
The observational approach
Making observations within species – the polar
bear
Stirling (1974) described the hunting strategies of 288
polar bears:
“sneak and pounce”
“jump and crush”
“sit and wait”
The obseravtional approach
Making observations within species – the polar
bear
Stirling (1974) described the hunting strategies of 288
polar bears:
1 “sneak and pounce”
The observational approach
Making observations within species – the polar
bear
Stirling (1974) described the hunting strategies of 288
polar bears:
1 “sneak and pounce”
54 “jump and crush”
The observational approach
Making observations within species – the polar
bear
Stirling (1974) described the hunting strategies of 288
polar bears:
1 “sneak and pounce”
54 “jump and crush”
233 “sit and wait”
The observational approach
Making observations within species – the polar
bear
Stirling (1974) described the hunting strategies of 288
polar bears:
1 “sneak and pounce”
54 “jump and crush”
233 “sit and wait”
Why then are polar bears white?
The observational approach
Making observations within species – the polar
bear
Observation: polar bears are black when
photographed under UV light (i.e., the coat absorbs
UV light)
The observational approach
Making observations within species – the polar
bear
Observation: polar bears are black when
photographed under UV light (i.e., the coat absorbs
UV light)
Hypothesis: Polar bears evolved a white coat to
serve as a “solar heat collector”
The observational approach
Making observations within species – the polar
bear
Observation: polar bears are black when
photographed under UV light (i.e., the coat absorbs
UV light)
Hypothesis: Polar bears evolved a white coat to
serve as a “solar heat collector”
How could this be tested?
Other explanations?
1. Sexual selection?
Other explanations?
1. Sexual selection?
2. Perhaps the initial advantage was
camouflage?
The comparative approach
Performing comparisons among species
The comparative approach: testes size
in fruit bats & flying foxes
The comparative approach
Performing comparisons among species
Observation: Testes size is highly variable among
species.
The comparative approach
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
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
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!
Adaptation Reminders
• Polar bear example= Must be careful in
carrying out the adaptations program.
Adaptation Reminders
• Polar bear example= Must be careful in
carrying out the adaptations program.
• Cannot just accept a hypothesis
because it is plausible.
Adaptation Reminders
• Polar bear example= Must be careful in
carrying out the adaptations program.
• Cannot just accept a hypothesis
because it is plausible.
• Have to test alternative explanations
Adaptation Reminders
• Polar bear example= Must be careful in
carrying out the adaptations program.
• Cannot just accept a hypothesis because it is
plausible.
• Have to test alternative explanations
• Differences among species are not always
adaptive!
Adaptation Reminders
• Polar bear example= Must be careful in
carrying out the adaptations program.
• Cannot just accept a hypothesis because it is
plausible.
• Have to test alternative explanations
• Differences among species are not always
adaptive
• Not every adaptation is perfect
Adaptation Reminders
• Polar bear example= Must be careful in
carrying out the adaptations program.
• Cannot just accept a hypothesis because it is
plausible.
• Have to test alternative explanations
• Differences among species are not always
adaptive
• Not every adaptation is perfect
• Not every trait of an organism is adaptive.
Adaptation questions:
• If a trait is not an adaptive trait how can it
persist?
• Why certain populations (or species) do not
possess certain traits that might be obviously
advantageous for them in the given/ changing
environment?
• If a trait is adaptive, is it always adaptive? Is
the organism stuck with the trait forever?