Transcript Chapter 1 Art Slides

Adaptation & Speciation

Normally over 2 days, going to ≥ slide 18 on day
one, but we do not have this luxury this term.
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Adaptation
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An improvement to an organism over time
Changes a population to better fit its
environment
The result of natural selection acting on genetic
variation
Environments change and new genetic variation
arises, so adaptation never reaches perfection
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Adaptation

Matches organisms to their environment
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Adaptation:
1.
2.
3.
Matches organisms to environment
Can be complex
Accomplishes specific functions
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Populations Can Adjust
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Sometimes adaptations
can be rapid
Soapberry bugs, Fl
adapted to an
introduced species by
obtaining shorter beaks
in 30-50 years.
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Adaptations Are Not Perfect
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Natural selection has
limitations:
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Genetic constraints
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

No variation, no adapting
Multiple effects of
genes in development
Ecological trade-offs
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What is good for one thing
may hurt in another
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What are Species?

Members of a species
generally look alike
 Bald
eagles in Alaska (top) &
Colorado (bottom)
 But not always
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Species –are reproductively
isolated from other species
Barriers to reproduction
between species
Barriers to reproduction

Prevent a zygote from being formed
Ecological isolation –species physically separated
 Behavioral isolation –mating calls, rituals
 Mechanical isolation –physically unable to mate
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Chihuahua and wolf cannot mate
Gametic isolation –gametes do not fuse
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Barriers to reproduction
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Barriers after zygote has formed
Zygote dies –offspring is never born
 Hybrid performance –not as fit as parents

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Mules cannot reproduce w/ each other or w/
donkey or horse
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Some Species Interbreed
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But the species stay
distinct
Live at different
elevations:



Gray – lower
Gambel – higher
hybrids - intermediate
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Complications: Some Species Can
Interbreed
But the species stay
distinct for complex
reasons
 Chihuahua -> small dog
-> collie -> shepherd ->
wolf
 Cat and bobcat
 We will keep it simple &
ignore these

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Walking Sticks
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Adapting to match their environment (two mating pairs)
Striped form (L) is well-hidden among the needlelike leaves w/ stripes, solid form among solid leaves
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Walking Sticks
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The striped form of the species prefers needlelike leaves of the chemise (sheh-mēz) bush.
The solid-green form prefers the solid green
leaves of the wild lilac.
The two forms are more likely to survive on their
preferred plant.
 Predators
(birds) more likely to catch them if they are
not on their preferred plant.
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Walking Sticks
Is a complex adaptation, more than coloration.
 Lilac and chemise bush leaves have different
pulp, fiber, chemical contents, and plant toxins.
 The solid-green walking sticks have enzymes to
better digest the leaves of the wild lilac.
 The striped form has enzymes adapted to better
digest the leaves of the leaves of the chemise
bush.
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Walking Sticks

“Hybrid offspring” of a cross between
solid and striped parents are less fit than
offspring of a single form mating.
 Do
not blend as well on either Lilac or chemise
bush leaves.
 Predators are more likely to eat them.
 Do not digest either plant as well as single forms.
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Walking Sticks
Because “Hybrid offspring” (a solid & striped cross)
are less fit than “single form” offspring, the
population is adapting in one other way:
 Individuals prefer to mate with others of the
same color pattern.


In nature, the two forms do not see each other
much (they stay on their preferred plants).
Mating experiments done in the lab.
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Walking Sticks
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Population is diverging with
respect to alleles for:
 coloration,
 digestion,
 dealing with plant toxins,
 mating behavior.
Disruptive selection is
better adapting each form to
their preferred plant.
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W/ time, disruptive selection will further diverge the
two forms & further decrease their interbreeding.
When the two forms loose the ability to interbreed,
they will become two different species.
Lecture To Here!
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Speciation
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When one species splits to form two species
Results from reproductive isolation
Often, it is a secondary consequence of
changing populations
Occasionally, is a direct consequence of a
diverging population
 The
hybrid is less fit, walking sticks
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Speciation
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Without geographic isolation is called:

Sympatric speciation
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Such as chromosomal changes
Due to geographical isolation is called:
 Allopatric
speciation (N & S rim of Grand Canyon)
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Allopatric Speciation
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Geographical separation
prevents species from
mating
When reintroduced, they
no longer mate
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Sympatric Speciation: Lake Victoria Cichlids
Species reproductively
isolated from:
 Sexual selection &
mating behaviors
 Species differ in their
diets
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Rates of Speciation
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Rates differ in different organisms
Can occur in thousands or millions of years
 Walking
sticks, have a reason to evolve reproductive
isolation quickly, hybrids are less fit

speciation may occur in a couple thousand years.
 European
and N. American sycamore trees do not
have a reason to evolve reproductive isolation
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they were separated geographically 20 mya & do not
normally interbreed
speciation has not yet occurred
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Speciation
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The splitting of one species into two has
never been seen in animals
 check
back in a couple thousand years
Walking sticks
 Apple maggots (worms)
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Russian Mad Scientist
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Russian scientist who crossed
radishes with cabbage.
 He
wanted a plant where you
could eat both the roots and
the leaves (beets).
 Promised the Soviet Union he
could do it if given enough
funding.
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Russian Mad Scientist
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He crossed cabbage & radishes
 The
hybrid offspring were sterile
 The chromosomes did not match
in meiosis

Not a problem
 Plants
can be grafted (clones)
 He obtained many hybrid clones
 He grew the grafts for years
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Russian Mad Scientist
He was either very lucky or very insane
 In one plant, a freak chromosomal
abnormality occurred

 The
chromosomes doubled and were able to
match in meiosis
 This rarely happens
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He then bred the one fertile hybrid and
studied it (it could self-pollinate)
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Russian Mad Scientist
His breeding was a failure
 Instead of the leaves of a cabbage and the
roots of a radish, he got the leaves of a
radish and the roots of a cabbage!
 Yet, his creation could not breed with
either a cabbage or a radish, due to
chromosomal incompatibilities
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Russian Mad Scientist
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Look what his failure obtained:
Cabbage
Radishes
Cabbage
Radishes
Cab-Rad
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Russian Mad Scientist
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He had witnessed the birth of a new species
He obtained three species from two
Cabbage
Radishes
Cabbage
Radishes
Cab-Rad
 Not sure if it kept him from being sent to Siberia
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Implications of Adaptation and
Speciation
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Understanding used to combat diseases

HIV
 Bacteria
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Concept Quiz
Which of the following is not a true
example of an adaptation?
A.
B.
C.
Bats wanting to fly and developing wings
Spots on a leopard for camouflage
Long tongues in frogs for catching flies
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Selection Causing
Reproductive
Isolation
Fruit flies were
raised on two food
sources
 Flies preferred to
mate with others
raised on same
food source

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Concept Quiz
One species of frog in a pond splits into two
species because males develop two different
mating calls. This is an example of:
A.
B.
C.
Ecological isolation
Polyploidy
Behavioral isolation
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Concept Quiz
Which of the following is not a reproductive
isolation mechanism?
A.
B.
C.
Hybrid fertility
Zygote death
Gametic isolation
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