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