Download Speciation & Patterns of Evolution

Topics:
• Speciation and
Reproductive Isolation
• Patterns of Evolution
• Rates of Evolution
• Origin of Life
Speciation
Species: population whose members can
interbreed in nature and produce viable, fertile
offspring
Evolution: change in the allelic frequencies in a population
Speciation
• Anagenesis
– Phyletic evolution
– One species replaces
another
– Pattern of evolution
that results in linear
descent with no
branching or splitting
of the population.
- Cladogenesis
– Branching evolution
– When a new species branches out from a parent species
– evolutionary change and diversification resulting from
the branching off of new taxa from common ancestral
lineages
•Anagenesis
•Cladogenesis
Speciation
• Allopatric
Speciation
• Sympatric
Speciation
• Adaptive
Radiation
Animation
Allopatric Speciation
“speciation by geographic isolation”
• Caused by geographic isolation
– Mountain ranges, canyons, rivers, lakes
• Interbreeding is prevented
• Gene frequencies diverge due to
natural selection, mutation, or
genetic drift.
Allopatric Speciation
•
•
Can occur even if the barrier
is a little “porous,” that is,
even if a few individuals can
cross the barrier to mate
with members of the other
group.
In order for a speciation
even to be considered
“allopatric,” gene flow
between the soon-to-be
species must be greatly
reduced—but it doesn’t have
to be reduced completely to
zero.
Sympatric Speciation
Barriers to Reproduction (sexual)
Sympatric Speciation
• Without geographic isolation
• Examples:
–
–
–
–
–
–
–
–
Balanced Polymorphism
Polyploidy
Hybridization
Habitat isolation
Temporal isolation
Mechanical isolation
Behavioral isolation
Gametic isolation
Prezygotic
barriers
Postzygotic
barriers
•Prezygotic barriers
•PREVENT mating
•Postzygotic barriers
•Prevent the production of fertile offspring after mating has
occurred
Balanced Polymorphism
Sympatric
Speciation
• Maintain stable frequencies of two or more
phenotypic forms
– natural selection preserves variation
– heterozygote advantage (i.e. heterozygotes have the
highest relative fitness).
• Ex:
• sickle cell anemia.
– Population of insects that possess polymorphism for
color.
– Can only survive where they are camouflaged.
– Become reproductively isolated, and their gene pools
diverge creating new species.
Polyploidy
• When a cell has more than two complete sets
of chromosomes
• Common in plants
Sympatric
Speciation
– Causes: nondisjunction
– Plants that are polyploid cannot breed with
others of the same species that are not
polyploid
– The two groups become isolated from one
another
Hybridization
• When two closely related
species mate and produce
offspring along a
geographic boundary.
– Called a “hybrid zone”
• Hybrids adapt to the area
and eventually diverge from
both parents.
Parapatric
Speciation
Sympatric
Speciation
• Habitat isolation
– Species do not encounter one another
• Temporal Isolation
– Mating takes place at different times of the year
– Flowers open at different times of the day.
• Mechanical Isolation
– Male and female genitalia are structurally incompatible
•Behavioral Isolation
–Populations are capable of interbreeding, but have
different courtship rituals or other type of behavior.
–Do not recognizes another species as a mating
partner.
Gametic isolation
• Male gametes do not survive in the
environment of the female gamete or when
female gametes do not recognize male
gametes
Postzygotic isolating mechanisms
• Hybrid inviability
– Zygote fails to develop and
aborts
• Hybrid sterility
– Hybrids become functional
adults, but are sterile. (ex:
mule)
• Hybrid breakdown
– Offspring have reduced
viability or fertility
Adaptive Radiation
• The evolution of many
diversely adapted species
from a common ancestor
• Relatively rapid
• Usually occurs when a
population colonizes an area of
diverse geographic or
ecological conditions.
– New niches
• Each species becomes
specialized for a different set
of conditions.
lineage rapidly diversifies
lineage rapidly diversifies
Patterns
of
Evolution
Evolution: change in the allelic frequencies in a population
Patterns of Evolution
• Divergent Evolution
• Convergent Evolution
• Parallel Evolution
• Coevolution
Divergent Evolution
• Occurs when a
population becomes
isolated from the rest
of the species.
• Becomes exposed to
new selective
pressures
• Evolves into a new
species
Convergent Evolution
• When unrelated
species occupy
the same
environment
and are
subjected to
similar
selective
pressures.
• Show similar
adaptations.
•Ex: Whale and Shark
–Not related, but have similar
features that are adapted for
their environment.
Parallel Evolution
• Two related species that
have made similar
evolutionary adaptations
after their divergence
from a common ancestor.
• Ex: Marsupial mammals of
Australia and placental
mammals of North
America.
– Similar environments
Coevolution
Rates
of
Evolution
Evolution: change in the allelic frequencies in a population
Rates of Evolution
A.Punctuated
Equilibrium
B. Phyletic
Gradualism
Gradualism
• Organisms descend from a
common ancestor slowly
over a long period of time.
Punctuated Equilibrium
• Favored theory
• New species appear
suddenly after long
periods of stasis.
sporadically (by splitting) and occurs relatively quickly
History of Life
1.Life on Earth originated between 3.5 and 4.0 billion
years ago. (Anaerobic heterotrophic prokaryotes)
2.Prokaryotes dominated evolutionary history from 3.5 to
2.0 billion years ago
3.Oxygen began accumulating in the atmosphere about 2.7
billion years ago (Photosynthesis)
4.Single celled eukaryote began by 2.1 billion years ago.
(Theory of Endosymbiosis)
5.Multicellular eukaryotes evolved 1.2 billion years ago
6.Plants, fungi, and animals colonized the land about 500
million years ago.
The first cells may have originated by chemical evolution
on a young Earth
• Most scientists favor the hypothesis that life on Earth
developed from nonliving materials that became ordered into
aggregates that were capable of self-replication and metabolism.
• From the time of the Greeks until the 19th century, it was
common “knowledge” that life could arise from nonliving
matter, an idea called spontaneous generation.
• While this idea had been rejected by the late Renaissance for
macroscopic life, it persisted as an explanation for the rapid
growth of microorganisms in spoiled foods.
• In 1862, Louis
Pasteur conducted
broth experiments
that rejected the
idea of spontaneous
generation
even for microbes.
• A sterile broth
would “spoil” only
if microorganisms
could invade from
the environment.
Swan flask
-created the first
vaccine for rabies -pasteurization.
Early life:
• Under one hypothetical scenario this occurred in four
stages:
(1) The abiotic synthesis of small organic
molecules;
(2) The joining these small molecules into
polymers:
(3) The origin of self-replicating molecules;
(4) The packaging of these molecules into
“protobionts.”
• This hypothesis leads to predictions that can be tested in
the laboratory.
Protobionts: aggregates of abiotically produced molecules surrounded by a
membrane or membrane-like structure
• AI Oparin and J.B.S. Haldane
• 1920s
• Hypothesized separately that under the
conditions of early earth, organic
molecules could form.
• A"primeval soup" of organic molecules
could be created in an oxygen-less
atmosphere through the action of sunlight
AI Oparin
Could not
demonstrate
theory.
•J.B.S. Haldane
Stanley Miller and Harold Urey
• 1953, Tested the Oparin-Haldane hypothesis
Stanley Miller
Harold Urey
Stanley Miller and Harold Urey
• 1953, Tested the Oparin-Haldane hypothesis
•Proved that almost any
energy sources would have
converted the molecules in
the early atmosphere into
organic molecules like
amino acids
•Discharged sparks in an
“atmosphere” of
gases and water vapor
•Produced a variety of
amino acids and other
organic molecules
Sidney Fox
• Carried out similar experiments to Miller and
Urey
• He began with organic molecules and was able
to produce membrane-bound, cell-like
structures he called proteinoid microspheres.
-Early work demonstrated that under certain conditions
amino acids could spontaneously form small polypeptides
-studied the spontaneous formation of protein structures
EXTRAS…Additions
• Outbreeding
• Opposite of inbreeding
• Mating with individual that are not closely related
• Ex: plants that have male and female parts that mature at
different times
• Helps insure genetic diversity
• Evolutionary neutral traits
• Trait that have no selective value
• Ex: blood type, fingerprints
• Life on Earth-David Attenbourgh
Pt3-Video CLip