What is adaptation?

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What is adaptation?
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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

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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.

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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 pre-determined end goal in
  mind

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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

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What is the significance of these slides as they
relate to adaptation?
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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?

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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 pre-adaptation 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

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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

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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

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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 dont have
  the trait
• The obvious answer is not always the right one

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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?

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Three major approaches to determining adaptive
significance of traits

• Experiments
• Observational studies
• Comparative studies

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Experimentation
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Experimental exampleZonosemata (snowberry) flies
and jumping spiders

• What is being investigated?

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• 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?

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Experimental exampleZonosemata flies

• What are 3 hypotheses that might explain this
  behavior?

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Experimental exampleZonosemata flies

• What was the experimental set-up

• What were some of the controls used in the
  experiment and why was each important?

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Experimental exampleZonosemata flies

• What predictions were made?

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Experimental exampleZonosemata flies

• What were the experimental results?

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RESULTS
Retreat
Stalk and attack
Kill
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What important points of experimental design are
demonstrated in the Snowberry Fly example?
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Effective Controls

• What were the control groups in this experiment?
• Why were they important?
• Allow us to work towards eliminating competing
  hyotheses.

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Handling all treatments exactly alike

• What were some of the things considered here?
• Same arena
• Method of presentation of flies
• Timing of presentation
• Others?

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Radomization

• What needed to be randomized and why?
• Order the flies were presented in
• Others?

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Repetition

• 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.

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Observational Studies

• With Garter Snakes

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Observational Studies

• 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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Show they are choosing a particular temperature
more often than would happen by random movements

• 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.

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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.

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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 .

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Table 10.1
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Comparative Studies
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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

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Example of comparative study

• 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?

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Showed initial correlation between social group
size and testes size.
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But the data could be skewed by evolutionary
relationships.

• 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.
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But two data points is not very reliable for
making extended conclusions.
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Felsensteins method of phylogenetically
independent contrasts.
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When species diverge from a common ancestor does
the species that evolves larger group sizes also
evolve larger testes?
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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.
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Phenotypic Plasticity
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De Meesters first study with Daphnia
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• Took resting eggs from 3 different levels of
  sediment in a man-made pond (can remain viable
  for decades!)
• Reawakened the Daphnia and produced populations
  of 10 cloned genotypes from each of 3 time
  periods.
• One time period had no fish predators coexisting
  in the pond with the Daphnia
• One time period had heavy predation by fish
• The third had Some fish predation.
• Results?......

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De Meesters second experiment
No stocking
Heavy Stocking
Reduced stocking
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Conclusions

• Showed that selection for phenotypic plasticity
  has been selected for in a lake where fish are
  present, the Daphnia from the lake where fish are
  present were much more plastic in their ability
  to respond to light

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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

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Video demonstrating transitional adaptations

• Whale evolution
• You may review this video at
• http//www.pbs.org/wgbh/evolution/library/03/4/qui
  cktime/l_034_05.html

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Adaptations work with what is available

• Many structures are far from optimally designed

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The fact that everything evolves from something
else is just one reason why an organisms 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)
• The Pandas thumb
• Eye Development see the link at
  http//www.pbs.org/wgbh/evolution/library/01/1/qui
  cktime/l_011_01.html

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Tradeoffs
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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
• Giraffes long neck may allow to fight off
  competition but it sure makes getting a drink
  inconvenient, difficult and maybe even dangerous.
  

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A trade-off example The Begonia

• 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

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Constraints
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Two types of constraints
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• Developmental based on how an organism develops
  in embryo or how an organisms structure is
  related to function.
• Phylogenetic based on inheriting the needed
  genetic variation from its ancestors

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Constraints (developmental example)

• 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.

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Constraint - phylogentic

• Pigs cant fly
• Animals cant 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.

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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.

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Adaptive Compromise

• Sickle cell and Malaria

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End Day One Adaptation
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Definitions
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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
• A birds flight feathers (from feathery scales on
  certain dinosaurs, where they served the function
  of insulation)
• The vertebrate eye (from a series of
  light-sensitive organs).

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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 ear-wagging muscles.

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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.

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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
  inside-out.
• 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.

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Definition

• 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 pandas 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.

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Exercise on examples of some adaptations and
imperfections
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The End
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