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What is adaptation?
Adaptation


Comes from ad (to or toward) and aptus (a
fit)
Evolutionary context –
◦ genetically-based change in response to a
problem
◦ achieved through the process of natural
selection.
◦ A period of time passes before adjustment
occurs
Adaptation is both a process and a
state of being (a phenotypic trait or
character)

We identify traits as adaptations only when
they are evolved for the solution of a
specific problem (selected function or
purpose).

Adaptation - a working definition:
a genetically based trait or integrated suite
of traits that has evolved in response to
selection for the function that it currently
performs and that increases the fitness of its
possessor

Just because a trait has a specific effect does
not mean that the trait is adaptive for that
purpose.
Evolution is blind!


Selection acts only on what is before it and
not with an end goal in mind.
Selection may lead to adaptations that …
are either a further modification of traits
already present (by changing their use) or…

selection may act to eliminate traits

All of the trends in selection that cause traits
to change over time are adaptive but the
changes are not done with some predetermined end goal in mind
Identifying adaptations can be
difficult and care must be taken
Many traits evolved under one selective
regime but are now being used under a
very different selective regime.
 The current function may not reflect the
context in which the trait was originally
evolved
 Need to distinguish current utility from
historical origin

What is the
significance of
these slides as they
relate to
adaptation?
Giraffes
What kind of story do the slides tell us
 What was the original explanation for the
adaptive value of the Giraffe neck?
 What other possibilities have now been
investigated?
 Does the giraffe neck give any feeding
advantage to those who possess it?

If the giraffe neck was actually selected for
as a means of defeating other males in a
battle over females, then
the neck is now coopted for use in
feeding higher in the trees than other
organisms can.
 Sometimes the term pre-adaptation is
used for such co-opted traits But preadaptation is a bad label to use here.
 The term exaptation has been
suggested by Stephen Gould
 refer to situations in which traits perform
a certain function now but either arose
originally for some other function or had
no function at all originally

Gould has also proposed the use of the term
spandrel for an adaptation that originally
arose with no adaptive purpose at all but
now has adaptive value
In male giraffes if long necks were
originally adapted for fighting then their
current advantage for feeding would be
an exaptation (originally arose for a
different adaptive reason)
 but in females long necks would be a
spandrel since they originally arose with
no adaptive value for females but now
may impart a feeding advantage.
 Examples of exaptations:
bone tissue
skull sutures

Adaptationist program






Seeks to find adaptive explanation for
every trait in organisms
Much difference of opinion on this
approach
Everything is not adaptive. Some things
are actually maladaptive or non-adaptive.
Some traits or variations in traits are
actually selectively neutral
Adaptations are not always perfect
Need to keep in mind that Adaptation is
also constrained by compromises,
trade-offs and correlations with other
traits
We will discuss each of these ideas later
Various types of studies are involved in the
attempt to explain what is happening in an
evolutionary context
To determine that a trait is actually an
adaptation we need to….
 determine what the trait is for and then
….
 show that individuals that have that trait
actually contribute more genes to the
next generation than the individuals that
don’t have the trait
 The obvious answer is not always the
right one

Giraffe story in the text



What are the two
current hypotheses?
The case of the giraffe
demonstrates the
importance of being
able to look at things
with fresh eyes and
come up with
alternative hypotheses.
Examine the picture to
the left does it suggest
a third possible
hypothesis for long
necks?
Three major approaches to
determining adaptive significance of
traits
 Experiments
 Observational
studies
 Comparative studies
Experimentation
Experimental example
Zonosemata (snowberry) flies and
jumping spiders

What is being investigated?
Zebra Jumping spiders stalk their prey.
Warn others of their species off with leg waving behavior
A prey of the jumping spider, the snowberry fly, exhibits a
curious behavior that resembles the leg-waving of the
jumping spider.
QUESTION: Why do the flies wave their striped wings?
Experimental example
Zonosemata flies

What are 3 hypotheses that might explain
this behavior?
Experimental example
Zonosemata flies
•What was the experimental set-up

What were some of the controls used in the
experiment and why was each important?
 What
predictions were made?
Experimental example
Zonosemata flies

What were the experimental results?
Experimental example
Zonosemata flies
RESULTS
What important points of
experimental design are
demonstrated in the
Snowberry Fly example?
What were the control groups in this
experiment?
 Why were they important?
 Allow us to work towards eliminating
competing hyotheses.

Effective Controls

What were some of the things considered
here?
◦
◦
◦
◦
Same arena
Method of presentation of flies
Timing of presentation
Others?
Handling all treatments exactly
alike

What needed to be randomized and why?
◦ Order the flies were presented in
◦ Others?
Radomization
Sample size needs to be large enough for
statistical analyses.
 Replicated experiments reduce the
amount of distortion because sample size
is larger which lowers the amount of
bias.
 Allow the measurement of variation in
data points.

Repetition
Observational Studies
With Garter Snakes
When are these type of studies done?
In this method we need to show two
things:
1. Occurrence of trait is non random in
the population
2. The observed trait is adaptive
Example – Garter Snake study
How did this study show that snake
movements is an adaptation to control
body temperature?

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Observational Studies
Show they are choosing a
particular temperature more often
than would happen by random
movements

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Watched snakes, where they spent their time
and what their body temps were
Found that they maintain their body
temperatures between 28 and 32 degrees
Celsius.
Discovered options for thermoregulation
sun/shade, under rocks (thin, medium, thick),
or moving up or down in burrows.
Found that of the 3, all could be used
to effectively maintain desired
daytime temps but only rocks could
provide enough warmth at night
Studied thin, medium and thick rocks.
 Predicted only medium rocks work for
the right temps both night and day.
 Most snakes found under rocks.

Now have to show that being
under medium rocks is not
random behavior
Compared availability of thin, medium
and thick rocks in the habitat to the
frequency that each was used by garter
snakes
 All rocks are equally represented in the
habitat so if random events, the snakes
should be found equally under each
type of rock.
 Results ….

Table 10.1
Comparative Studies
Tests for patterns across species
 Proper application of comparative
methods requires knowledge of the
evolutionary relationships among the
species under study.
 Example bat studies

Comparative Studies
Bats:
Is the larger size of testes in some bats
adaptive due to sperm competition?
 Do bats from larger social groups have
larger testes because there is more
competition for passing on their genes?

Example of comparative study
Showed initial correlation between
social group size and testes size.
But the data could be skewed by
evolutionary relationships.
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The testes size could still be related to
who evolved from whom.
Perhaps the larger testes groups are
simply from one common ancestor and
the smaller from another.
Need to do a correction for this
If we replace the
individual points
for A, B and C and
for D,E and F with
a single point
representing their
most recent
common ancestor
we get….
But two data
points is not very
reliable for
making extended
conclusions.
Felsenstein’s method of phylogenetically
independent contrasts.
Plot sister species
independently
When species diverge from
a common ancestor does the
species that evolves larger
group sizes also evolve
larger testes?
Drag point
closest to the
vertical axis
to the origin
Erase lines
Bat results: show that when a
bat species evolved larger
group sizes than its sister
species, it also tended to evolve
larger testes for its body size.
Phenotypic Plasticity
De Meester’s first study with Daphnia
De Meester’s second
experiment No stocking
Heavy Stocking
Reduced stocking
Every Adaptive Trait Evolves from
something else

In order to show that one thing has evolved
from similar structures in ancestors must be
able to …
1. Establish the ancestral condition
2. Understand the transformational sequence,
how and why the characters changed through
time
Video demonstrating
transitional adaptations
Whale evolution
You may review this video at
http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_03
4_05.html
Adaptations work with
what is available
Many structures are far from optimally designed
The fact that everything evolves from
something else is just one reason why an
organism’s traits, even when clearly
adaptive, are often imperfect

Contrivances - less than optimally
designed structures (if interested visit
http://www.talkorigins.org/faqs/jury-rigged.html)
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The Panda’s thumb
Eye Development see the link at
http://www.pbs.org/wgbh/evolution/library
/01/1/quicktime/l_011_01.html
Tradeoffs
Trade-offs
Two evolutionary forces may work on the
same part from different directions and the
resources devoted to one body part or
function may be stolen resources from
another part or function
 Giraffe’s long neck may allow to fight off
competition but it sure makes getting a drink
inconvenient, difficult and maybe even
dangerous.

A trade-off example
The Begonia
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In Begonias there is a trade-off between the
size of female flowers and the size of the
inflorescence. Even though larger female
flowers attract more pollinators, the female
flowers remain smaller than optimal for
pollination because bees also visit larger
inflorescences and larger inflorescences can
not contain individual flowers as large as the
optimal flower size alone would dictate
trade-off between the number of female
flowers and individual flower size may be
dictated by two things. 1) more flowers,
more seeds and 2) perhaps more bees will
be attracted to larger inflorescences
Constraints
Two types of constraints


Developmental – based on how an
organism develops in embryo or how an
organism’s structure is related to function.
Phylogenetic – based on inheriting the
needed genetic variation from its
ancestors
Constraints (developmental example)
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A behavior or trait that would be adaptive is
physiologically or mechanically impossible.
Why does the Fuchsia retain its flowers and
turn them red for 5 days AFTER pollination,
when pollinators are no longer visiting, the
flowers are of no more use but are still tapping
needed resources.
Investigations showed that it was not a cue for
pollinators telling them which flowers to visit.
Turns out that pollen tubes need to grow
through the area of the abscission layer for
the petals and if petals are dropped too soon
the pollen tube never makes it to the ovules.
So the petals need to remain for at least 4
days after pollination for fertilization to take
place.
Constraint - phylogentic
Pigs can’t fly
 Animals can’t do photosynthesis
 Beetle example on page 388-389

◦ Need to be able to detoxify the chemicals in
individual host plants they may prey upon.
◦ Showed genetic variation which allows beetles to
attack different host plants, and detoxify the new
hosts unique chemical defenses depends on
which phylogenetic group the beetles belong to.
Constraints in Arthropods
Arthropods inherited both an
exoskeleton and jointed legs. These
traits have opened up many
opportunities in arthropod evolution,
but they have also blocked other
possibilities. Can you think of any
constraints on the size that arthropods
will reach?
Molting: Molting is more hazardous for larger animals.
Exoskeleton strength: The exoskeleton may not be strong
enough to support larger animals.
Respiration: Many arthropods can only get enough oxygen
to support small bodies.
Sickle cell and Malaria
Adaptive Compromise
End Day One Adaptation
Definitions
Some Definitions
Preadaptation(exaptation): A character
that was adaptive under a prior set of
conditions and later provides the initial
stage for evolution of a new adaptation
under a different set of conditions.
 Examples:
1. A bird’s flight feathers (from feathery
scales on certain dinosaurs, where they
served the function of insulation);
2. The vertebrate eye (from a series of lightsensitive organs).

Definition
Vestigial structure: an anatomical structure
found in all or most normal individuals of an
extant species; typically very small in size,
and with apparently little or no important
function now.
 Such parts typically would be found in
ancestors of this species, but as larger and
clearly functional structures.
 An example would be the human earwagging muscles.

Definition
Atavism (Atavistic structure): a vestigial
structure found in only a small fraction of
the normal members of an extant species
 Example
 The rudimentary thigh bone found in
about 5% of individual whales.

Definition
Contrivance: A structure modified and
used for a function which is different from
the original (or previous) function for that
structure in an ancestor.
 Example
 The vertebrate eye

 The design of the vertebrate retina is “insideout.”
 The retina is behind the nerves that form the
optic nerve.
 Where the optic nerve leaves the eye, there is
a hole, which results in a blind spot.
Definition
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Imperfection: A “contrivance” which still
retains some of the features of its ancestral
source structure, to a greater or lesser
degree; clearly not fully or perfectly
“adapted” to its new function, but serving
adequately.
Example
The panda’s “thumb” is an example here,
as are the many contrivances found in
orchid flowers.
This term could also be applied to vestigial
or atavistic structures.
Exercise on examples of some
adaptations and imperfections
The End