Transcript Natural Selection

Biological
Evolution
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Evolutionary Bush -thousands of earlier and
later branches.
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At any given moment (e.g. the
‘present’), all we see is current
diversity…
all extinct forms are gone (99.9%)
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Four Causes of Evolution
1. Mutation: fundamental origin of all genetic
(DNA) change.
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Four Causes of Evolution
1. Mutation: fundamental origin of all genetic
(DNA) change.
Point mutation
…some at base-pair level
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Four Causes of Evolution
1. Mutation: fundamental origin of all
genetic (DNA) change.
Crossing-over
…others at grosser
chromosome level
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Four Causes of Evolution
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolated populations accumulate
different mutations over time.
In a continuous
population, genetic
novelty can spread
locally.
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Four Causes of Evolution
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolated populations
accumulate different mutations over time.
Local spreading of alleles
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Four Causes of Evolution
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolated populations
accumulate different mutations over time.
Local spreading of alleles
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Four Causes of Evolution
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolated populations accumulate
different mutations over time.
Spreading process
known as ‘gene
flow’.
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Four Causes of Evolution
But in
discontinuous
populations, gene
flow is blocked.
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Four Causes of Evolution
Variations accumulate
without inter-demic
exchange
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Four Causes of Evolution
Of course, this
works at many
loci
simultaneously
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Four Causes of Evolution
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolation  accumulate
mutations
3. Founder Effect: sampling bias during
immigration. When a new population is
formed, its genetic composition depends
largely on the gene frequencies within the
group of first settlers.
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Founder Effect.--
Human example: your tribe had to
live near the Bering land bridge…
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Founder Effect.--
…to invade & settle the ‘New World’!
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Galapagos Finches
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Audeskirk & Audeskirk, 1993
Four Causes of Evolution
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolation  accumulation of
mutations
3. Founder Effect: immigrant sampling bias.
4. Natural Selection: differential
reproduction of individuals in the same
population based on genetic differences
among them.
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Four Causes of Evolution
1. Mutation: fundamental genetic shifts.
2. Genetic Drift: isolation  accumulation of
mutations
3. Founder Effect: immigrant sampling bias.
4. Natural Selection: reproductive race
These 4 interact synergistically
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Evidence of
Evolution
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Evidence of Evolution
1. Biogeography:
Geographical distribution of species
Evidence of Evolution
2. Fossil Record:
Fossils and the order in
which they appear in layers
of sedimentary rock
(strongest evidence)
Fossils
• Oldest fossils are the
approximately 3.465
billion-year-old
microfossils from the
Apex Chert, Australia
– colonies of
cyanobacteria
(formerly called bluegreen algae) which
built real reefs
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Fossils
1600's - Danish scientist Nicholas Steno studied
the relative positions of sedimentary rocks
– Layering is the most obvious feature of sedimentary
rocks
• formed particle by particle and bed by bed, and the layers
are piled one on top of the other
• any sequence of layered rocks, a given bed must be older
than any bed on top of it
– Law of Superposition is fundamental to the
interpretation of Earth history, because at any one
location it indicates the relative ages of rock layers
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and the fossils in them.
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Relative and Absolute Dating
• Relative Dating
• Absolute Dating
• Can determine the age of
fossil with respect to
another rock or fossil.
• You compare the depth of
a fossils position, layers.
• Some drawbacks include
limitations on accuracy.
• Can determine the age of
a fossil IN YEARS.
• You determine the age by
finding the amount of
radioactive and
nonradioactive isoptope
in a specimen.
• Some drawbacks are that
it is difficult to perform in
a lab.
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Types of Radioactive Isotopes
• Carbon 14
• Potassium 40
• Use for more recent
fossils (60,000 yrs
old)
• Can be used with
high accuracy
• Half life of 5,730
years
• Decays into
Nitrogen
• Used for older fossils
• Half life of 1.3 billion
years
• Decays into Calcium
• Less common
element
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Half-life for a given radioisotope is the time for half the
radioactive nuclei in any sample to undergo
radioactive decay
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Half-life for a given radioisotope is the time for half the
radioactive nuclei in any sample to undergo
radioactive decay
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Evidence of Evolution
3. Taxonomy:
Classification of life forms.
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4. Homologous
structures:
Structures that
are similar
because of
common
ancestry
(comparative
anatomy)
Evidence of
Evolution
Turtle
Alligator
Bird
Typical primitive
fish
Mammals
Evidence of Evolution
5. Comparative
Embryology:
Study of
structures that
appear during
embryonic
development
Evidence of Evolution
6. Molecular biology:
DNA and proteins (amino acids)
History of
Theories of Evolution
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Old Theories of Evolution
• Jean Baptiste Lamarck (early 1800’s)
proposed:
“The inheritance of acquired
characteristics”
He proposed that by using or not using its
body parts, an individual tends to develop
certain characteristics, which it passes on
to its offspring.
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“The Inheritance of Acquired
Characteristics”
• Example:
A giraffe acquired its long neck
because its ancestor stretched higher
and higher into the trees to reach
leaves, and that the animal’s
increasingly lengthened neck was
passed on to its offspring.
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Charles Darwin
• Darwin set sail on the H.M.S. Beagle
(1831-1836) to survey the south seas
(mainly South America and the
Galapagos Islands) to collect plants and
animals.
• On the Galapagos Islands, Darwin
observed species that lived no where else
in the world.
• These observations led Darwin to write
a book
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Giant Tortoises of the Galápagos Islands
Pinta
Pinta Island
Intermediate
shell
Fernandina
Isabela
Tower
Marchena
James
Santa
Cruz
Santa Fe
Hood Island
Floreana
Hood
Saddle-backed
shell
Isabela Island
Dome-shaped shell
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http://www.galapagosislands.com
Charles Darwin
Wrote in 1859:
“On the Origin of Species by Means of
Natural Selection”
Two main conclusions:
1. Species were not created in their
present form, but evolved from
ancestral species.
2. Proposed a mechanism for evolution:
NATURAL SELECTION
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Darwin’s Observations
1. Most species produce more offspring
than can be supported by the
environment
2. Environmental resources are limited
3. Most populations are stable in size
4. Individuals vary greatly in their
characteristics (phenotypes)
5. Variations that survive are inherited.
(genotypes)
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Natural Selection
• Individuals with favorable traits are
more likely to leave more offspring
better suited for their environment
• Also known as “Differential
Reproduction”
Example:
English peppered
moth (Biston betularia)
Modes of Action
• Natural selection has three modes of action:
1. Stabilizing selection
2. Directional selection
3. Diversifying selection
Number
of
Individuals
Small
Large
Size of individuals
1. Stabilizing Selection
• Acts upon extremes and
favors the intermediate.
Number
of
Individuals
Small
Large
Size of individuals
2. Directional Selection
• Favors variants of one
extreme.
Number
of
Individuals
Small
Large
Size of individuals
3. Disruptive Selection
•Favors variants of
opposite extremes.
Number
of
Individuals
Small
Large
Size of individuals
Evidence for
Natural Selection
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Artificial Selection
• The selective breeding of
domesticated plants and animals
by man.
• Question: What’s the ancestor of
the domesticated dog?
Biodiversity
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Biodiversity
• Biodiversity
– increases with speciation
– decreases with extinction
• Give-and-take between speciation
and extinction  changes in
biodiversity
• Extinction creates evolutionary
opportunities for adaptive radiation
of surviving species
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Interpretations of Speciation
• Two theories:
1.Gradualist Model (NeoDarwinian):
Slow changes in species
overtime
2.Punctuated Equilibrium:
Evolution occurs in spurts of
relatively rapid change
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Adaptive
Radiation
Emergence of
numerous species
from a common
ancestor introduced
to new and diverse
environments.
Example:
Hawaiian
Honeycreepers
Convergent Evolution
• Species from different evolutionary
branches may come to resemble one
another if they live in very similar
environments.
• Example:
1. Ostrich (Africa) and Emu (Australia).
2. Sidewinder (Mojave Desert) and
Horned Viper (Middle East Desert)
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Coevolution
• Evolutionary change, in which one
species act as a selective force on a
second species, inducing adaptations
that in turn act as selective force on the
first species.
Example:
1. Acacia ants and Acacia trees
2. Yucca Plants and Yucca moths
3. Lichen
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Extinction
• Extinction of a species occurs when it
ceases to exist; may follow environmental
change - if the species does not evolve
• Evolution and extinction are affected by:
– large scale movements of continents
– gradual climate changes due to continental
drift or orbit changes
– rapid climate changes due to catastrophic
events
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Extinction
• Background extinction - species disappear
at a low rate as local conditions change
• Mass extinction - catastrophic, widespread events --> abrupt increase in
extinction rate
• Five mass extinctions in past 500 million
years
• Adaptive radiation - new species evolve
during recovery period following mass
extinction
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http://www.geog.ouc.bc.ca/physgeog/contents/9h.html
Mass Extinctions
Date of the
Extinction
Event
Percent
Species
Lost
65 mya
(million
years ago)
85
213 mya
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Dinosaurs, plants (except ferns and
seed bearing plants), marine
vertebrates and invertebrates. Most
mammals, birds, turtles, crocodiles,
lizards, snakes, and amphibians were
unaffected.
Marine vertebrates and invertebrates
248 mya
380 mya
450 mya
75-95
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Marine vertebrates and invertebrates
Marine invertebrates
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Marine invertebrates
Species Affected
Community
Relationships
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Niche
a species’ functional role in its
ecosystem; includes anything affecting
species survival and reproduction
1. Range of tolerance for various physical and
chemical conditions
2. Types of resources used
3. Interactions with living and nonliving
components of ecosystems
4. Role played in flow of energy and matter cycling
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Niche is
the species’ occupation
and its
Habitat
location of species
(its address)
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Niche
Fundamental niche: set of
conditions under which a
species might exist in the
absence of interactions
with other species
Realized niche: more
restricted set of conditions
under which the species
actually exists due to
interactions with other species
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Species Interaction
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Competition
any interaction between two or more
species for a resource that causes a
decrease in the population growth or
distribution of one of the species
1.
2.
3.
4.
Resource competition
Preemptive competition
Exploitation competition
Interference competition
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Competition
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Competition
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Predation: prey adaptations
• Avoid detection
– camouflage, mimics,
– diurnal/nocturnal
• Avoid capture
– flee
– resist
– escape
• Disrupt handling (prevent being eaten)
– struggle?
– protection, toxins
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Rewards of Mutualism
• Food: energy and nutrients
• Protection:
– from other species (competition, predation)
– from the physical environment (shelter)
• Gamete or zygote dispersal (the most
common of all)
• Pollination and fruit dispersal (between
plants and animals).
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Pollination (hummingbird/bee
and flowering plants)
• animals visit flowers to collect nectar
and incidentally carry pollen from one
flower to another
• animals get food and the plant get a
pollination service
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Yucca moth and yucca
• Yucca’s only
pollinator is the
yucca moth. Hence
entirely dependent
on it for dispersal.
• Yucca moth
caterpillar’s only
food is yucca seeds.
• Yucca moth lives in
yucca and receives
shelter from plant.
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Lichen (Fungi-algae)
• Symbiotic relationship of algae and
fungae…results in very different
growth formas with and without
symbiont.
• What are the benefits to the fungus?
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Seed Disperser
• Many birds and mammals consume
fruits and incidentally disperse the
seeds contained in those fruits
– Animals get food and the plant gets
seed dispersal (often with fertilizer)
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Ant-tended plants
• Ants live inside
swollen Acacia
thorns or hollow
stems, e.g. Cecropia
trees.
• Patrol for
caterpillars or leaf
predators and storm
out to repel
intruders…including
you!
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Commensalists
• Benefit from the
host at almost no
cost to the host
• Eyelash mite and
humans
• Us and starlings or
house sparrows
• Sharks and remora
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Parasites
Parasites: draw resources from host
without killing the host (at least in the
short term).
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