Evolution. Content 1. An introduction to evolution 2. Historical view (the evolutionary thinking) 3....

Evolution

Content• 1. An introduction to evolution

• 2. Historical view (the evolutionary thinking)

• 3. Genetic variation

• 4. Mechanisms: the processes of evolution

• 5. Microevolution vs Macroevolution

• 6. Speciation

• 7. Issues on evolution

Evolution

Evolution = Change.

Biological Evolution = Change in the intrinsic qualities of life over time.

NOT progressive change.

What can change?

Characteristics of species

Number of species

EvolutionMicroevolution = Change in the

genetic qualities of populations within a species over time.

Macroevolution = Change in the number of species and the formation of groups of species.

Speciation = formation of species

Results of Evolution

• Anagenesis = change within a species lineage(number not increase)

• Cladogenesis = change and diversification

History: Early 1800’s

Natural Theology

Discover God’s plan, study nature.

Essentialism = Organisms are imperfect reflections of perfect eternal “essences.” (invariant)

Natural groups reflect the essential groups in the mind of God.

History: Early 1800’sPaleontology = study of fossils.

Fossil = preserved remnant of an organism that lived in the past

Certain fossils only found in certain rock strata (layers).

Some organisms are extinct!

Earth = VERY OLD

Sedimentary Rocks = layered rocks formed by settling particles.

Sedimentary Rocks & Fossils

oldest layer

youngest layer

Sedimentary Rocks & Fossils

Dead Thing

Sedimentary Rocks & Fossils

Fossil (Dead Thing)

Sedimentary Rocks & Fossils

Fossil (Dead Thing)

Sedimentary Rocks & Fossils

Fossil (Dead Thing)

EROSION

Sedimentary Rocks & Fossils

Fossil (Dead Thing)

Sedimentary Rocks

Geologic Time ScaleGeologic scale based on the fossil

record. (time divisions UNequal)

Eras = four largest time periods (Precambrian --> Paleozoic --> Mesozoic --> Cenozoic)

Periods subdivide eras.

Mass Extinction = extinction of a large proportion of existing species.

They separate many eras or periods.

Geologic Time Scale

Cenozoic

Mesozoic

Paleozoic

Precambrian

extinction of dinosaursfirst flowering plants

first dinosaurs & mammals

“fern” forests form coal

first vertebratesfirst land plants & animals

near present oxygen levels

Eons

Eons = hundreds of millions of years in duration(บรมยุ�ค)

Eras(มหายุ�ค)

period(ยุ�ค)

epochs.

Biostratigraphy: The organisation of sedimentary rocks into units on the basis of the fossils they contain

Biostratigraphy:

Charles Darwin

Mid-1800’s, Charles Darwin

Studied medicine & theology

Traveled on H. M. S. Beagle

Bred pigeons

The Origin of Species, 1859TWO big ideas

Common Descent (old idea)

Natural Selection (new idea)

Natural SelectionMechanism of change

within one species. (Proposed by Darwin.)

Microevolutionary process.

First evidence from plant and animal breeding by humans

to create domestic forms.

Natural SelectionPopulations can grow tremendously.

In nature, populations remain stable in size due to limited resources (K).

THEREFORE, there is a struggle to survive and reproduce within species.

Organisms vary in inheritable characteristics (genetic).

THEREFORE, reproduction varies based on differences in inherited traits.

Natural Selection

DEFINITION

Differential reproduction (survival) based on

differences in inherited characteristics.

NOT “survival of the fittest”

Population

Population

Population

Population

Population

Population

Population

FitnessFITNESS = the relative contribution

of an individual to the next generation

More fit = more surviving offspring

Less fit = fewer surviving offspring

“Survival of the fittest” = circular, non biological statement

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Adaptation

Adaptation = characteristic that results from natural selection also...

a trait that enhances the reproductive success of the bearer.

Not ALL characteristics of organisms are “adaptations.”

Difficult to provide evidence that a characteristic is truly an adaptation.

Laboratory Selection

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Microevolution

Sexual Selection

“Special” Kinds of Selection

Natural Selection = differential reproduction (survival) based on differences in inheritable characteristics (different alleles).

Sexual Selection = natural selection based on mate choice.

Artificial Selection = natural selection due to conscious human choice. (e.g., dogs, wheat)

Sexual Selection

Artificial Selection

Artificial Selection

p. 399

Population Genetics

Population = localized group of individuals of the same species

Population genetics = studies the genetic variation within populations

Genotype = the genes (alleles) possessed by an organism

Phenotype = the physical characteristics of an organism

Genetics “Review”

Genes (DNA) in cells direct cell activities.

Most cells have TWO copies of every gene. (DIPLOID)

One copy from each parent.

Sperm or egg have ONE copy of every gene. (HAPLOID)

Genetics “Review”

Genetics “Review”

The same gene can have different forms (Alleles).

E.g., blue iris allele and brown iris allele of eye color gene

Diploid individual with the same 2 alleles = homozygote.

Diploid individual with 2 different alleles = heterozygote.

Genetics

Gene “A” has 2 alleles,

“A” and “a.”

AA or aa = homozygotes.

Aa = heterozygotes.

AA, Aa, and aa = genotypes.

Calculation of allele frequencies.

Population GeneticsGene pool = all the alleles in a

population

Genetic structure = frequencies (%) of alleles and genotypes in a population.

Mendelian population = interbreeding group within a population.

Hardy Weinberg

Hardy-Weinberg Theorem = describes a population that is NOT evolving.

p2 + 2pq + q2 = 1

p = frequency of A in the pop.

q = frequency of a in the pop.

p + q = 1

P(A)=p P(a)=q

P(A)=p

P(a)=q

AA=p2 Aa =pq

AA + 2Aa + aa = p2 + 2pq + q2 = 1

Random mating

aA=pq aa=q2

(p+q) 2 = 1

p+q = 1

Hardy Weinberg

p2 + 2pq + q2 = 1

p2 = frequency of AA in the pop.

2pq = frequency of Aa in the pop.

q2 = frequency of aa in the pop.

Hardy-Weinbergp2 + 2pq + q2 = 1

The frequency of AA in a population at H.-W. equilibrium is

0.25.

What is the frequency of Aa in this population?

Hardy-Weinberg

p2 + 2pq + q2 = 1

p2 = 0.25

p = 0.5

p + q = 1 0.5 + q = 1

q = 0.5

Hardy-Weinberg

p2 + 2pq + q2 = 1

p = 0.5 q = 0.5

2pq = frequency of Aa

2(0.5)(0.5) = frequency of Aa

0.5 = frequency of Aa

Microevolutionary ProcessesMicroevolution = small

scale evolutionary changes.

Natural Selection

Non-random mating

Genetic Drift

Gene Flow (Migration)

Mutation

MutationMutation = introduction of random

genetic variation. Source of new alleles.

THE SOURCE of variation.

Change in the DNA (in a sex cell).

Relatively rare and random.

Some chemicals can increase mutation rate (mutagens).

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Gene Flow

Gene flow = Gaining alleles from or losing alleles to another population.

Fertile individuals (emigration & immigration)

Seeds

Pollen

Gametes

Genetic Drift

Changes in the gene pool of a (small) population due to chance.

Chance =

random catastrophes

random individuals begin a pop.

genes randomly passed on to offspring

computer_drift_v2[1].swf

Genetic Drift

Genetic Drift

Genetic Drift

Genetic Drift

Genetic Drift

Population Bottleneck = genetic drift in small remnant population that later becomes larger. Result: a large genetically similar population

Founder effect = genetic drift in small founding population that later becomes larger. Example: polydactyly in the Amish

Population Bottleneck

p. 403

Population Bottleneck

time

#Much

Genetic Drift

GeneticVariation

No GeneticVariation

LargePopulation

LargePopulation

SmallPopulation

Cheetahs

Founder Effect

time

#

time

#

GeneticVariation

No GeneticVariation

Zoo Animals

Nonrandom MatingAssortative Mating = preferentially

mating with either similar or different genotypes.

Inbreeding = reproducing with relatives; increases homozygosity.(More likely to get 2 copies of the same bad gene. INCEST TABOO)

Outbreeding = reproducing with non-relatives; increases heterozygosity.

Natural Selection

Phenotype can be determined by a single gene or by many genes.

Stabilizing selection = removes extremes.

Directional selection = Removes ONE extreme.

Disruptive selection = Removes intermediates; favors extremes.

Quantitative Characters

One Gene Characteristic

#

Many Gene Characteristic

#

Directional Selection

#

p. 405

Distribution

#

p. 405

Directional selection

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Stabilizing Selection

#

p. 405

Distribution

#

p. 405

Disruptive Selection

#

p. 405

MicroevolutionMutation - source of new variation

Gene Flow - redistributes variation

Genetic Drift - reduces variation (by chance)

Non-random mating - maintains (outbreeding) or reduces (inbreeding) variation

Natural Selection - reduces variation (due to environment)

Hardy-Weinberg Assumptions

NO EVOLUTION

no mutation

population is genetically isolated

very large population size

random mating

no natural selection

Hardy-WeinbergAre the assumptions of Hardy-

Weinberg likely to be met?

Nope.

Why is the equation useful?

Modification by terms for pop. size, selection, non-random mating, etc. more realistically model real populations.

EVOLUTION

mutation

gene flow

genetic drift

assortative mating

natural selection

Hardy-Weinberg Assumptions

Decreasing VariationGenetic Drift - reduces variation (by

chance)

Inbreeding - reduces variation by increasing homozygosity

Natural Selection - reduces variation (due to environment); disadvantaged alleles disappear

Maintaining Variation

Mutation - creates new alleles

Neutral Alleles - do not affect the fitness of an organism; are not removed by natural selection

Subpopulations - selection different in different areas but gene flow keeps them “mixing”

Dislocation of European bison's subpopulations in Ukraine

Maintaining VariationGene Flow through Sexual Reproduction

- new combinations of alleles

Polymorphism - two genotypes favored by selection (often frequency dependent)e.g., right mouthed & left mouthed scale eating fishes

Heterozygote Advantage - heterozygote parents produce some homozygote offspring

Right mouthed & Left mouthed scale eating fishes

conspicuously asymmetrical left-bending (left) and right-bending (right) individuals of the scale-eating cichlid fish Perissodus microlepis from Lake Tanganyika.

(Photo courtesy of A Meyer.)Palmer Journal of Biology 2010 9:11   doi:10.1186/jbiol218

Sickle Cell DiseaseHbnHbn = “normal” red blood cells; no

sickle cell disease

HbnHbs = some sickled red blood cells some normal; mild sickle cell disease and some protection from malaria

HbsHbs = sickled red blood cells; sickle cell disease causing death and some protection from malaria

Sickle Cell Disease In malarial areas:

sickle cell malaria

HbnHbn none highly susceptible

HbnHbs mild low susceptibility

HbsHbs death low susceptibility

Relationship of Phenotype and Genotype

The Genotype codes for the Phenotype

-Almost all enzymes are proteins. -Almost all traits are produced by the action of proteins.

Genotype PhenotypeGenotype and phenotype are not exactly

correlated.

Environment is important.

e.g., human height

Phenotypic plasticity - the production of different phenotypes in response to different environments.

e.g., white oak leaves

• A change in the environment also can affect the phenotype.

• Pinkness in flamingos is not encoded into their genotype.

• The food they eat makes their phenotype white or pink.

Evolutionary ConstraintAll conceivable mutations are not

possible.

The organism must still function.

All jawed vertebrates have a body plan with 2 pairs of paired appendages.

No six legged vertebrates.

Evolution must work with what it has.Major reorganization very rare.

Evolutionary Constraint

p. 411

• Why couldn't terrestrial arthropods evolve to be as large as elephants?

• What is an evolutionary constraint?

The laws of Physics and Inheritance

• Arthropods inherited both an exoskeleton and jointed legs.

• These traits have opened up many opportunities in arthropod evolution, but they have also blocked other possibilities.

• In particular, there are three constraints on the size of terrestrial arthropods: – Molting: Molting is more hazardous for larger animals. – Exoskeleton strength: The exoskeleton may not be

strong enough to support larger animals. – Respiration: Many arthropods can only get enough

oxygen to support small bodies.

The land-dwelling coconut crab weighs in at 5 kg (over 10lbs). For these giants, molting is a serious commitment: they may spend a whole month in a deep burrow wriggling out of the old skin and waiting for the new one to firm up!

crab3[1].swfIs the physics of molting a constraint on arthropod size?

You've just seen that molting out of the exoskeleton may limit the size of terrestrial arthropods. Does the exoskeleton cause other problems for outsized arthropods? To figure out the answer, we'll see what happens to the exoskeleton and the muscles that move it when an arthropod is scaled up.

Exoskeleton strength: Blowing up ants

What would happen to an ant if it were scaled up, keeping all its body parts in proportion? Each ant below is twice the size of the previous one. See what happens when it gets up to go forage for food.

ant_walk2[1].swf

Exoskeleton strength: A solution?

So is there any solution to this problem? Well, wider tubes are stronger than narrower ones. Perhaps if we gave our giant ant extra-wide legs with an extra-thick exoskeleton, it wouldn't suffer so many broken limbs. Does this ant look like it might be a winner?

Extra large means extra heavy

ele_ant_walk[1].swf

The Crustacean/Spider Model

The Insect Model

Water/air passes over gills/book lungs and oxygen diffuses into the blood. The blood carries oxygen throughout

the body.

Tracheae and trachioles (essentially ductwork) allow air to circulate throughout the body — oxygen diffuses into the tissues near individual cells.

The Crustacean/Spider Model

The Insect Model

Water/air passes over gills/book lungs and oxygen diffuses into the blood. The blood carries oxygen throughout the body.

Tracheae and tracheoles (essentially ductwork) allow air to circulate throughout the body — oxygen diffuses into the tissues near individual cells.

The Crustacean/Spider Model

The Insect Model

Water/air passes over gills/book lungs and oxygen diffuses into the blood. The blood carries oxygen throughout the body.

Test.png

Test.png

celltracheae[1].swfgillsbooklungs[1].swf

Respiration: Gotta have oxygen

All animals, including insects, need oxygen. Without it, their cells die. Insects don't have lungs and their "blood" doesn't carry oxygen. Insect cells get oxygen via a direct link to the air outside — a network of tubes, called tracheae let oxygen reach cells deep within the insect.

All animals, including insects, need oxygen. Without it, their cells die. Insects don't have lungs and their "blood" doesn't carry oxygen. Insect cells get oxygen via a direct link to the air outside — a network of tubes, called tracheae let oxygen reach cells deep within the insect.

The tubes below represent the tracheae of three dragonflies. In this model, each tube supplies a gut cell with oxygen — the larger the dragonfly, the longer the tube. The blue dots represent oxygen molecules. See how oxygen moves through the tubes. The gut cell in the biggest dragonfly is not doing too well because it is not getting enough oxygen. There is a limit to the length of tracheae (and thus to the size of the dragonfly) that can provide every cell with sufficient oxygen.

dragonfl_air[1].swf

Conclusion• Evolution is an undirected process, constrained

– by physical laws (such as gravity)– by genetics (which might, for example, encode the

directions for building breathing organs in a particular way), and

– by the environment (which might not, for example, contain a niche for a large, slow-moving, and fragile ant).

• In the case of the arthropods, the exoskeleton — a useful adaptation for body support, protection and water retention as well as their respiratory system, may have brought evolutionary constraints along with benefits.