Transcript Ch.16Speciation ppt

EVOLUTION &
SPECIATION
VOCABULARY REVIEW
• EVOLUTION – CHANGE OVER TIME
• NATURAL SELECTION - INDIVIDUALS
BETTER ADAPTED TO THE
ENVIRONMENT ARE ABLE TO
SURVIVE & REPRODUCE.
– A.K.A. “SURVIVAL OF THE FITTEST”
Charles Darwin
• Wrote in 1859:
“On the Origin of Species
by Means of Natural Selection”
• Two main points:
1. Species were not created in their present
form, but evolved from ancestral species.
2. Proposed a mechanism for evolution:
NATURAL SELECTION
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)
- light and dark phases
Darwin’s 5 points
1. Population has variations.
2. Some variations are favorable.
3. More offspring are produced than
survive
4. Those that survive have favorable
traits.
5. A population will change over time.
Artificial Selection
• The selective breeding of domesticated
plants and animals by man.
• Question:
What’s the ancestor of the domesticated dog?
• Answer: WOLF
Evidence of Evolution
1. Biogeography:
Geographical distribution of species.
2. Fossil Record:
Fossils and the order in which they appear
in layers of sedimentary rock (strongest
evidence).
NEW VOCABULARY
• POPULATION – GROUP OF
INDIVIDUALS OF SAME SPECIES
THAT INTERBREED
• GENE POOL – COMMON GROUP OF
ALL GENES PRESENT IN A
POPULATION
Gene Pool
Combined genetic
info. of all
members
Allele frequency is
# of times
alleles occur
Variation in Populations
2 processes can
lead to this:
Mutations change in DNA
sequence
Gene Shuffling –
from sexual
reproduction
a. Bottleneck Effect
• Genetic drift (reduction of alleles in a population)
resulting from a disaster that drastically reduces
population size.
• Examples:
1. Earthquakes
2. Volcano’s
•
•
•
Genetic drift can cause big losses of genetic variation for small
populations. It reduces genetic variation.
Population bottlenecks occur when a population’s size is reduced for at
least one generation.
This is illustrated by the bags of marbles shown below, where, in
generation 2, an unusually small draw creates a bottleneck
•
Reduced genetic variation means that the population may not be able to adapt
to new selection pressures, such as climatic change or a shift in available
resources, because the genetic variation that selection would act on may have
already drifted out of the population.
•
An example of a bottleneck:
Northern elephant seals have reduced genetic variation probably because of a population bottleneck
humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals
at the end of the 19th century. Their population has since rebounded to over 30,000—but their genes still
carry the marks of this bottleneck: they have much less genetic variation than a population of southern
elephant seals that was not so intensely hunted.
Genetic Drift changes populations…….
• Random change in allele
frequency causes an allele to
become common
• Founder Effect:
a cause of genetic
drift attributable to
colonization by a
limited number of
individuals from a
parent population
• Non-random mating: inbreeding and
assortive mating (both shift
frequencies of different genotypes)
• Assortative mating occurs when individuals select mates
non-randomly from within their population, on the basis of a
trait that both they and their mates express.
Founder Effect
• Genetic drift resulting from the colonization
of a new location by a small number of
individuals.
• Results in random change of the gene pool.
• Example:
1. Islands (first Darwin finch)
Five Mechanisms of Microevolution
1. Islands (first Darwin finch)
2. Gene Flow:
The gain or loss of alleles from a
population by the movement of individuals
or gametes.
• Immigration or emigration.
• Gene Flow:
genetic exchange
due to the
migration of fertile
individuals or
gametes between
populations
(reduces
differences
between
populations)
Five Mechanisms of Microevolution
3. Mutation:
Change in an organism’s DNA that
creates a new allele.
4. Non-random mating:
The selection of mates other than
by chance.
5. Natural selection:
Differential reproduction.
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.
Greyhounds
Bred for speed
Number
of
Individuals
Small
Large
Size of individuals
3. Diversifying Selection
• Favors variants of opposite extremes.
Number
of
Individuals
Small
Large
Size of individuals
Speciation
• The evolution of new species.
Reproductive Barriers
• Any mechanism that impedes two species
from producing fertile and/or viable hybrid
offspring.
• Two barriers:
1. Pre-zygotic barriers
prevent fertilization
2. Post-zygotic barriers
prevents fertilized egg from
developing into a fertile adult
1. Pre-zygotic Barriers
a. Temporal isolation:
Breeding occurs at different times for
different species.
b. Habitat isolation:
Species breed in different habitats.
c. Behavioral isolation:
Little or no sexual attraction between
species.
1. Pre-zygotic Barriers
d. Mechanical isolation:
Structural differences prevent gamete
exchange.
e. Gametic isolation:
Gametes die before uniting with gametes
of other species, or gametes fail to unite.
2. Post-zygotic Barriers
a. Hybrid inviability:
Hybrid zygotes fail to develop or fail to
reach sexual maturity.
b. Hybrid sterility:
Hybrid fails to produce functional gametes.
c. Hybrid breakdown:
Offspring of hybrids are weak or infertile.
• One oft-cited example of a postzygotic mating barrier
occurs when horses and donkeys,
• two different species, interbreed to produce mules.
Mules, as a hybrid offspring, are generally robust
organisms. However, the genetic incompatibility of
the horse and the donkey result in sterility in the
mule.
• Because mules are infertile, gene flow between the
horse and donkey is effectively blocked, even though
they are able to produce hybrid offspring.
• Natural Selection:
differential
success in
reproduction;
only form of
microevolution
that adapts a
population to its
environment
Sexual selection
• Sexual
dimorphism:
secondary sex
characteristic
distinction
• Sexual selection:
selection towards
secondary sex
characteristics
that leads to
sexual dimorphism
• Sexual dimorphism is
a phenotypic difference
between males and females of
the same species.
Evolution of Populations
Occurs when there
is a change in
relative
frequency of
alleles
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
mutation!
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
Generation 3: 0.76 not resistant
0.24 resistant
How natural selection works
Resistance to antibacterial soap
Generation 1: 1.00 not resistant
0.00 resistant
Generation 2: 0.96 not resistant
0.04 resistant
Generation 3: 0.76 not resistant
0.24 resistant
Generation 4: 0.12 not resistant
0.88 resistant
Phenotype Expression
• Depends on
how many
genes control
that trait
Single-Gene vs. Polygenic Traits
Single-Gene:
2 Distinct Phenotypes (EG: tongue rolling)
Polygenic:
Many Phenotypes
Allele Frequencies
Natural Selection
Single Gene
Traits
Genetic Drift
Polygenic
Traits
Directional
Selection
Stabilizing Selection
Disruptive Selection
Natural Selection on Polygenic Traits
• Shifts to
middle range
• Shifts to
2 extremes
• Shifts to
1 extreme
Conditions needed for Genetic
Equilibrium
Hardy-Weinberg Principle
• The concept that the shuffling of genes that
occur during sexual reproduction, by itself,
cannot change the overall genetic makeup
of a population.
Hardy-Weinberg Principle
• This principle will be maintained in nature
only if all five of the following conditions are
met:
1.
2.
3.
4.
5.
Very large population
Isolation from other populations
No net mutations
Random mating
No natural selection
Hardy-Weinberg Principle
• Remember:
If these conditions are met, the
population is at equilibrium.
• This means “No Change” or “No
Evolution”.
Macroevolution
• The origin of taxonomic groups higher
than the species level.
Microevolution
• A change in a population’s gene pool
over a secession of generations.
• Evolutionary changes in species over
relatively brief periods of geological time.
Five Mechanisms of Microevolution
1. Genetic drift:
Change in the gene pool of a small
population due to chance.
• Two examples:
a. Bottleneck effect
b. Founder effect
SPECIATION
• THE FORMATION OF NEW SPECIES
• AS NEW SPECIES EVOLVE,
POPULATIONS BECOME
REPRODUCTIVELY ISOLATED
• REPRODUCTIVE ISOLATION –
MEMEBERS OF 2 POPULATIONS
CANNOT INTERBREED & PRODUCE
FERTILE OFFSPRING.
3 ISOLATING MECHANISMS……..
• BEHAVIORAL ISOLATION- CAPABLE OF
BREEDING BUT HAVE DIFFERENCES IN
COURTSHIP RITUALS (EX. MEADOWLARKS)
• GEOGRAPHICAL ISOLATION – SEPARATED BY
GEOGRAPHIC BARRIERS LIKE RIVERS,
MOUNTAINS, OR BODIES OF WATER (EX.
SQUIRREL)
• TEMPORAL ISOLATION – 2 OR MORE SPECIES
REPRODUCE AT DIFFERENT TIMES.
Table 23.1a
Tigon
Result of male tiger
and female lion
mating incaptivity.
Offspring are infertile.
Separated both
geographically and
ecologically.
Liger
Result of male lion and female
tiger mating in captivity.
Offspring are infertile.
Table 23.1b
Fig. 23.6
Four species of leopard frogs: differ in their
mating calls. Hybrids are inviable.
Allopatric Speciation
• Induced when the ancestral population
becomes separated by a geographical
barrier.
• Example:
Grand Canyon and ground squirrels
These squirrels live on opposite sides of the Grand
Canyon. This is an example of allopatric speciation.
Hawaiian Honeycreepers
An example of adaptive radiation –
these species all diverged from a
common ancestor (founder species)
FOUNDER SPECIES
Adaptive Radiation
• Emergence of numerous species from a
common ancestor introduced to new and
diverse environments.
• Example:
Darwin’s Finches
SPECIATION IN DARWIN’S
FINCHES
• SPECIAITON IN THE GALAPAGOS
FINCHES OCCURRED BY:
- FOUNDING OF A NEW POPULATION,
- GEOGRAPHIC ISOLATION which led to - REPRODUCTIVE ISOLATION and
CHANGES IN THE NEW POPULATION’S
GENE POOL due to COMPETITION.
Evidence of Evolution
1. Fossil Record
2. Geographic Distribution of Living
Species
3. Homologous Body structures
4. Similarities in Embryology
Evidence of
Evolution
Fossil Record
provides evidence
that living things
have evolved
Fossils show the
history of life on
earth and how
different groups of
organisms have
changed over time
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)
Flying
Squirrel
Sugar
Glider
Marsupial Mammals
Convergent
Evolution
and
Analogous
Structures
Placental mammals
Mammalia
Rat like
common
ancestor
Review
Big Question!!!
How did life arise on the big blue planet??
 Scientists attempt to answer this
question scientifically.
Relative Dating
versus
Absolute Dating
Relative Dating
• Can determine a
fossil’s relative
age
• Performed by
estimating fossil
age compared
with that of
other fossils
• Drawbacks –
provides no info
about age in
years
Absolute dating
• Can determine the
absolute age in
numbers
• Is performed by
radioactive dating –
based on the amount
of remaining
radioactive isotopes
remain
• Drawbacks - part of
the fossil is
destroyed during the
test
Carbon-14 Dating
Fossil Formation
Big Bang Theory
 A cosmic explosion that hurled matter and in all
directions created the universe 10-20 billion years
ago
 Evidence
 it explains why distant galaxies are traveling
away from us at great speeds
 Cosmic radiation from the explosion can be
observed
 The Big Bang theory probably will never be
proven; consequentially, leaving a number of tough,
unanswered questions.
What was early earth like?
Earth was Hot!!
Little or no oxygen
Gasses in atmosphere:
Hydrogen cyanide (poison to you!)
Hydrogen sulfide
Carbon dioxide
Carbon monoxide
Nitrogen
So how did the earth
get oxygen?
 Some of that oxygen was generated by
photosynthetic cyanobacteria
 Some came from the chemical
separation of water molecules into
oxygen and hydrogen.
 Oxygen drove some life
forms to extinction
 Others evolved ways of
using oxygen for respiration
How did life begin?
Miller and Urey’s
Experiment
 Passed sparks
through a mixture of
hydrogen methane
ammonia and water
 This produced
amino acids – the
building blocks of life
Miller’s
experiment
suggests that
lightning could
have produced
amino acids
How can simple amino
acids result in life?
There are 3 theories
1. Formation of microspheres
 Large organic molecules can
sometimes form tiny proteinoid
microspheres
 Store and release energy, selectively
permeable membranes, may have
acquired more characteristics of living
cells
nd
2
Hypothesis for Life
Evolution of RNA to DNA
• RNA was assembled
from simple organic
molecules in a
primordial soup
• RNA was able to
replicate itself and
eventually form DNA
• Not scientifically
proven to be possible
rd
3
Theory of Life
Endosymbiotic theory
eukaryotic cells
arose from living
communities formed
by prokaryotic
organisms
Ancient prokaryotes
entered primitive
eukaryotic cells and
remained there as
organelles