Topics:Topics:
• Speciation and Reproductive Isolation
• Patterns of Evolution
• Rates of Evolution
• Origin of Life
SpeciatioSpeciationn
Evolution: change in the allelic frequencies in a population
Species: population whose members can interbreed in nature and produce viable,
fertile offspring
• 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
Speciation
•Anagenesis•Cladogenesis
•Allopatric Speciation
•Sympatric Speciation
•Adaptive Radiation
Speciation
Animation
• 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“speciation by geographic isolation”
• 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.
Allopatric 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
Sympatric Speciation
•Prezygotic barriers
•PREVENT mating
•Postzygotic barriers
•Prevent the production of fertile offspring after mating has occurred
Prezygotic
barriersPostzygotic barriers
• Maintain stable frequencies of two or more phenotypic forms– natural selection preserves variation – heterozygote advantage (i.e. heterozygotes have the
highest relative fitness). • sickle cell anemia.
• Ex: – 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.
Balanced Polymorphism Sympatric Speciation
• When a cell has more than two complete sets of chromosomes
• Common in plants– 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
Polyploidy Sympatric Speciation
• 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.
Hybridization Parapatric Speciation
• Habitat isolationHabitat isolation– Species do not encounter one another
• Temporal IsolationTemporal Isolation– Mating takes place at different times of the year– Flowers open at different times of the day.Flowers open at different times of the day.
• Mechanical IsolationMechanical Isolation– Male and female genitalia are structurally incompatible
Sympatric Speciation
•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.
• Male gametes do not survive in the environment of the female gamete or when female gametes do not recognize male gametes
Gametic isolation
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
• 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.
Adaptive Radiationlineage rapidly diversifies
lineage rapidly diversifies
Patterns Patterns of of
EvolutionEvolutionEvolution: change in the allelic frequencies in a
population
Patterns of EvolutionPatterns of Evolution
•Divergent Evolution•Convergent Evolution•Parallel Evolution•Coevolution
• Occurs when a population becomes isolated from the rest of the species.
• Becomes exposed to new selective pressures
• Evolves into a new species
Divergent Evolution
• When unrelated species occupy the same environment and are subjected to similar selective pressures.
• Show similar adaptations.
Convergent Evolution
•Ex: Whale and SharkEx: Whale and Shark–Not related, but have similar Not related, but have similar features that are adapted for features that are adapted for their environment.their environment.
• 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
Parallel Evolution
•Predators and their prey •Parasites and their hosts•Plant-eating animals and the plants upon which they feed •One example of coevolution is between plants and the animals that pollinate them.
Coevolutio
n is the
joint
change of
two or
more
species in
close
interaction.
Coevolution
Rates of
EvolutionEvolution: change in the allelic frequencies in a
population
Rates of Evolution
A.Punctuated Equilibrium
B.Phyletic Gradualism
• Organisms descend from a common ancestor slowly over a long period of time.
Gradualism
• Favored theory• New species appear
suddenly after long periods of stasis.
Punctuated Equilibrium
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.
• 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.
The first cells may have originated by chemical evolution on a young Earth
• In 1862, Louis Pasteur conductedbroth experimentsthat rejected the idea of spontaneousgeneration even for microbes.
• A sterile brothwould “spoil” onlyif microorganismscould invade fromthe environment.
-created the first vaccine for rabies -pasteurization.
Swan flask
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
•J.B.S. Haldane
Could not demonstrate
theory.
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 hypothesis1953, 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” ofgases and water vapor
•Produced a variety of amino acids and other organic molecules
Sidney FoxSidney 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.
-studied the spontaneous formation of protein structures
-Early work demonstrated that under certain conditions amino acids could spontaneously form small polypeptides
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