Transcript UNIT II – PLANT DIVERSITY

Evolution
Diversity of Life
1
• Evolution is
the slow,
gradual
change in a
population of
organisms
over a long
period of
time
2
Lamarck’s Theory of Evolution
• One Of First
Scientists To
Understand That
Change Occurs
Over Time
• Stated that
Changes Are
Adaptations To
Environment
acquired in an
organism’s lifetime
• Said acquired
changes were
passed to offspring
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Lamarck’s Theory of
Evolution
• Inheritance of Acquired
Characteristics
• Proposed That By Selective Use
Or Disuse Of Organs, Organisms
Acquired Or Lost Certain Traits
During Their Lifetime
• These Traits Could Then Be
Passed On To Their Offspring
• Over Time This Led To New
Species
4
Lamarck’s Theory of Evolution
• Use & Disuse Organisms Could
Change The Size Or
Shape Of Organs By
Using Them Or Not
Using Them
• Blacksmiths & Their
Sons (muscular arms)
• Giraffe’s Necks
Longer from
stretching)
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Lamarck’s Theory of
Evolution
• Inheritance Of Acquired Traits
– Traits Acquired During Ones Lifetime
Would Be Passed To Offspring
Clipped ears of dogs could be passed to offspring!
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Lamarck’s Mistakes
• Lamarck Did NOT Know how
traits were inherited (Traits
are passed through genes)
• Genes Are NOT Changed By
Activities In Life
• Change Through Mutation
Occurs Before An Organism Is
Born
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Darwin’s Conclusion
• Production of more
individuals than can be
supported by the
environment leads to a
struggle for existence
among individuals
• Only a fraction of
offspring survive each
generation
• Survival of the Fittest
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Darwin’s Observations
• Individuals of a
population vary
extensively in their
characteristics with
no two individuals
being exactly alike.
• Much of this
variation between
individuals is
inheritable.
10
Darwin’s Conclusion
• Individuals who
inherit
characteristics most
fit for their
environment are
likely to leave more
offspring than less
fit individuals
• Called Natural
Selection
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Darwin’
s
Theory
of
Evolutio
•The unequal ability of individuals
n
to survive and reproduce leads to a
gradual change in a population,
with favorable characteristics
accumulating over generations
(natural selection)
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EVOLUTION
Evidence and Mechanisms
for Evolution
Evidence for Evolution
Evidence in organisms:
• 1. Biochemistry & DNA
• 2. Fossil Evidence
• 3. Embryology
• 4. Structures
1. Biochemistry & Molecular Biology
• Our genes provide an ‘evolutionary record’
• If we evolved from a common ancestor:
– We should have same genetic molecule
(DNA)
– We should use the DNA in the same way
(dogma)
– Portions of our DNA should be the same
(and they are)
• Closely related organisms share large portions
of DNA (amino acid) sequence…
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Human
THR LEU SER GLU LEU HIS CYS ASP LYS LEU HIS VAL ASP PRO GLU
Chimpanzee
THR LEU SER GLU LEU HIS CYS ASP LYS LEU HIS VAL ASP PRO GLU
Gorilla
THR LEU SER GLU LEU HIS CYS ASP LYS LEU HIS VAL ASP PRO GLU
Rhesus Monkey GLN LEU SER GLU LEU HIS CYS ASP LYS LEU HIS VAL ASP PRO GLU
Horse
ALA LEU SER GLU LEU HIS CYS ASP LYS LEU HIS VAL ASP PRO GLU
Kangaroo
LYS LEU SER GLU LEU HIS CYS ASP LYS LEU HIS VAL ASP PRO GLU
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Human
ASN PHE ARG LEU LEU GLY ASN VAL LEU VAL CYS VAL LEU ALA HIS
Chimpanzee
ASN PHE ARG LEU LEU GLY ASN VAL LEU VAL CYS VAL LEU ALA HIS
Gorilla
ASN PHE LYS LEU LEU GLY ASN VAL LEU VAL CYS VAL LEU ALA HIS
Rhesus Monkey ASN PHE LYS LEU LEU GLY ASN VAL LEU VAL CYS VAL LEU ALA HIS
Horse
ASN PHE ARG LEU LEU GLY ASN VAL LEU ALA LEU VAL VAL ALA ARG
Kangaroo
ASN PHE LYS LEU LEU GLY ASN ILE ILE VAL ILE CYS LEU ALA GLU
Cladogram – a graphic representation
that shows relatedness of organisms
2. FOSSIL EVIDENCE FOR
EVOLUTION
• Fossils – any trace left by a previous
organism
• Rocks, ice, amber, bogs, tar, etc.
• Most are preserved in sedimentary
rocks
• Oldest rocks (fossils) have simplest
life forms and found deeper in the
crust
Evidence for Evolution – The Fossil Record
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3. Developmental Biology
• Early embryos of different mammal
species look very much alike – they
share common features, such as gills,
eyes, ear holes, tails
4. Comparative Anatomy
• Homologous structures: Share same
common origin or structure, but may
have different functions.
• For example: same bone structure
found in a human arm, bat wing,
dolphin flipper, bird wing…
• Analogous structures: organs that
have similar functions in different
organisms, but do not share a
common evolutionary origin or same
structures
• For example:Wings of insects vs.
wings of birds
Vestigial organs
• Vestigial strucutres: organs or
parts of organs that are nonfunctional and degenerate
• For example: wisdom teeth, appendix
• Vestigial leg bones in snakes and
whales
What does this say
about whales?
Why do snakes have
two lungs but only
one is functional?
Four Types of Evolutionary
Mechanisms
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•
•
•
Natural Selection
Mutation
Genetic Drift
Gene Flow
Natural Selection
•
There is variation in traits.
For example, some beetles are green and some are brown.
•
There is differential reproduction.
Since the environment can't support unlimited population growth, not all individuals
get to reproduce to their full potential. In this example, green beetles tend to get
eaten by birds and survive to reproduce less often than brown beetles do.
•
There is heredity.
The surviving brown beetles have brown baby beetles because this trait has a genetic
basis.
•
End result:
The more advantageous trait, brown coloration, which allows the beetle to have more
offspring, becomes more common in the population. If this process continues,
eventually, all individuals in the population will be brown.
If you have variation, differential reproduction, and heredity, you will have evolution
by natural selection as an outcome. It is as simple as that.
Types of Natural Selection
• Stabilizing
– Baby weight
– Pays to be average
• Directional
– Peppered moth
– Pays to be different
• Disruptive
– Lizards on volcanic
rock
Disruptive
• Disruptive selection: selection that tends to
divide a population into two categories
• A species of spadefoot toads that lives in Oregon has
two color phases that are genetically determined so that
these toads are either light or dark in color. Spadefoot
toads live in arid regions and like most prey animals are
active at night. A variety of predators feed on these
toads. Spadefoot toads prefer dry habitats and are
mostly nocturnal. These toads burrow into the ground to
keep from drying out during the day and can stay
underground for long periods of time when conditions are
too dry.
In the Diamond Craters area of Oregon the soil is
very dark due to the dark volcanic material deposited in
the area. Almost all of the spadefoot toads living in this
area are the dark variety while those from the
surrounding desert are the light variety.
Directional
• directional selection: selection that favors
individuals with an extreme value of some
feature, so that a population will shift in one
direction
• African elephants typically have large tusks.
The ivory in the tusks is highly valued by some
people, so hunters have hunted and killed
elephants to tear out their tusks and sell them
(usually illegally) for decades. Some African
elephants have a rare trait -- they never
develop tusks at all. In 1930, about 1 percent of
all elephants had no tusks. The ivory hunters
didn't bother killing them because there was no
ivory to recover. Meanwhile, elephants with
tusks were killed off by the hundreds, many of
them before they ever had a chance to
reproduce.
Stabilizing selection:
selection that tends to
maintain some feature of a
population at an average
value
Mutation
• Inheritable change in genetic
material
– Ex: bacteria and viruses
Genetic Drift
• Change in allele frequency due to
chance
– Ex: disease, population crash, natural
disaster
Gene Flow
• Movement of alleles in and out of a
population
• Ex: immigration or emigration of
organisms
Selection Pressures may cause the
organism to:
• Adapt if the genes are already
present
• Migrate to another area
• Become extinct
ADAPTATIONS
• ADAPTATIONS are traits that
promote the survival and
reproductive success of an organism
in a particular environment.
• Specific behavioral, Physiological,
Physical, Chemical, Mimicry that arise
during evolution, as a response to
specific environmental pressures.
Behavioral and Physiological Adaptations
• Behavioral
– Ex: hibernation, bird
calls for mating
• Physiological –
bodily processes
– Ex: sweating, fever
Physical Adaptations
• Thorns on a cactus
to avoid predation
• Cuticle on a leaf to
prevent water loss
Chemical
• Release of a chemical
substance to ward
off predators
– Ex: poison ivy, skunks
releasing odor, squid
releasing ink
Mimicry and protective
coloration
• Mimicry: a harmless
species may resemble a
dangerous species.
– Ex: Monarch butterfly
is toxic, but Viceroy is
not.
– Ex: Coral snake:
venomous vs. impostor
•
•
“Red on black, venom lack. Red on
yellow, kill a fellow”
Migration Types
• Geographic isolation – a physical
barrier prevents reproduction
Reproductive isolation –
physical changes prevent
reproduction
•Lack of "fit" between sexual organs:
Hard to imagine for us, but a big issue for insects with
variably-shaped genitalia!
These damselfly penises illustrate just how complex
insect genitalia may be.
•Offspring inviability or sterility:
All that courting and mating is wasted if the offspring of
matings between the two groups do not survive or cannot
reproduce.
Temporal isolation – timing
of mating prevents
reproduction
The evolution of different mating location, mating time, or
mating rituals:
Genetically-based changes to these aspects of mating could
complete the process of reproductive isolation and speciation.
For example, bowerbirds (shown below) construct elaborate
bowers and decorate them with different colors in order to
woo females. If two incipient species evolved differences in
this mating ritual, it might permanently isolate them and
complete the process of speciation.
All of which can lead
to speciation – the
development of a new
species
Extinction
• The loss of a species
due to selective
pressures
• Variation – difference
within species reduces
the chances of
extinction
• Biodiversity –
differences among
species
Darwin’s Finches – speciation and
divergent evolution
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•
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Divergent evolution – a
single species becomes
adapted to different
environment and becomes
less alike
Darwin believed that at one
time, all the finches
originated from one species.
Due to their variation in
their beak sizes, the
finches fed on different
diets.
In order to survive, the
finches moved to areas
where their diet could be
found.
Coevolution
• Coevolution: the long term
evolutionary adjustment of one
group of organisms to another.
• Coevolution is a reciprocal process
in which characteristics of one
organism evolve in response to
specific characteristics of another
Coevolution
• Mutual evolutionary influence between two
species (the evolution of two species totally
dependent on each other). Each of the species
involved exerts selective pressure on the other,
so they evolve together.
• For example: Moth and Yucca plant
• Yucca flowers are a certain shape so only that tiny moth
can pollinate them. The moths lay their eggs in the yucca
flowers and the larvae (caterpillars) live in the developing
ovary and eat yucca seeds.
Examples of co-evolution:
symbiosis
• There’s ANTS in PLANTS!
• Acacia trees and ants –
coevolution.
Pollination: coevolution of
plants and insects
• Flowers & insects/birds
coevolution for pollination.