EVOLUTIONARY PROCESSES AND PATTERNS

EVOLUTIONARY PROCESSES AND PATTERNS

• Theories of species creations and diversity prior to evolutionary theory

• Theory of Special Creation– Species are unchanged

through time and are independent of one another

– All species were created independently by “…the Trinity on the October 26th 4004 B.C. at 9:00 in the morning” Archbishop James Ussher 1664.



• Theory of Spontaneous Generation– New organisms (species) may

suddenly appear wherever conditions are suitable

– Some new life-forms arise spontaneously from streams, soils, rotting meat, and other nonliving materials; not all life arises directly from living organisms



• Prior to Darwin and Wallace - Lamarck– New simple life forms arise by

spontaneous generation and change over time into more complex life forms

– Individuals change in response to their environment and the changes are passed to the next generation.


• Theories of Evolution• Darwin and Wallace

– Species are related to one another, and they change over time, thus species existing today have descended, with modifications, from other preexisting species.

– Natural selection acts on individuals; individuals with certain favorable characteristics will produce more offspring.

Evolution

• What is evolution?

• Microevolution: survival through the inheritance of favorable characteristics – mutations – selection

• Macroevolution: progression of biodiversity through geological time – speciation – extinction

Evolution• How does it occur?

Evolution

• Species – group of potentially interbreeding natural populations capable of producing viable offspring

• Speciation (through reproductive isolation) – division of populations

(allopatric speciation) – barriers to reproduction

(sympatric speciation)

Evolution

• Allopatric Speciation

Evolution• Sympatric

Speciation

?

Evolution• Parapatric

Speciation

?

Evolution• "All life comes from life"

– Modification of previously existing structures (homologous) – mammal forelimb structure

– Increasing resemblance of organs or organisms serving the same function (analogous) • insect wings vs. bird

wings (mimicry) • spurges vs. cacti • aloes vs. agaves • via Convergence

Darwinian Selection

• All natural selection results in evolution, but not all evolution is the product of natural selection.

• What is evolution?

• What is natural selection?

• What is an adaptation?

Darwinian Selection• All natural selection results in evolution, but not all evolution is

the product of natural selection.• What is evolution?

– Evolution is the change in allele frequencies (or traits) over time.

Darwinian Selection


• What is evolution?– Evolution is the change in allele frequencies (or traits)

over time.

• What is natural selection?

–


Darwinian Selection


• What is evolution?– Evolution is the change in allele frequencies (or

traits) over time.

• What is natural selection?– .


Darwinian Selection

•Sum it all up

Insects, spiders, nectar

Tools use to get insects

Leaves and fruit

Ticks off of iguanas etc.

Seeds

Darwinian Selection

Is there variation about a trait?

Darwinian Selection

Is the variation heritable and not the result of maternal effects?

Darwinian Selection

Is there an excess of individualsso that only some animals liveto reproduce?

Are resources limited?

Darwinian Selection

Is reproduction nonrandom?

The drought of 1977 eliminated seed set by most of the plants producing small soft seeds. Tribulus cistoides seeds are large and hard and became the dominant food item. Only large birds with deep beaks could defend resources and access the resources

Darwinian Selection

Is reproduction nonrandom?

Darwinian Selection

Did evolution occur?

The El Niño of 1983 produced 1359 mm of rain and lavish seed set by the small soft seeded plants. Birds with shallow beaks harvest these seeds more efficiently and thus reproduced better than birds with deep beaks, undoing the selection shown here. Fluctuating environmental conditions maintain both phenotypes.

Types of Selection

• Directional Selection

• Stabilizing Selection

• Disruptive selection

Directional Selection

• Phenotype at one extreme of population distribution has selective advantage.

• Leave more offspring• Mean for trait shifts

which way?

Types of Selection




Stabilizing Selection

• Intermediate phenotypes have selective advantage.

• What happens to the distribution for the trait?

Types of Selection




Disruptive Selection

• Intermediate phenotypes selected against

Darwinian Selection

• At what level does natural selection work?– Genes– Individual– Group– Population– Species

Darwinian Selection

• .

Darwinian Selection

Darwinian Selection

Darwinian Selection

Darwinian Selection

Darwinian Selection

Darwinian Selection

Darwinian Selection

Darwinian Selection

• The consequences of natural selection are expressed at the population level.– Natural selection, like all forms of evolution

results in a change in allele frequencies (or frequencies of a trait).

Genetic drift

• Genetic drift results in a gradual loss of genetic diversity

• Over time an individual locus and gene frequency will drift until one allele becomes fixed

Convergent Evolution

ISOLATION AND CONVERGENT EVOLUTIONConvergence

– Myrmecophagesanteaters, aardvark, aardwolf, numbat,

pangolins

ISOLATION AND CONVERGENT EVOLUTION

Convergence– Cursorial herbivores

pronghorn, capybara, guanaco, kangaroos

digestive tract, dentition, elongated limbs


• Batesian Mimcry– Benign species

resembles a noxious or dangerous species


• Mullerian Mimicry– Noxious species

resemble each other


• Mullerian Mimicry– Noxious species

resemble each other– Pitohui birds in New

Guinea– homobatrachotoxin in

skin and feathers

Convergent Evolution• Aggressive Mimicry

– Noxious or dangerous species resembles a benign one

– Zone-tailed Hawk

Coevolution

Association Effect on Species A

Effect on Species B

Parasitism Positive Negative

Commensalism Positive None

Mutualism Positive Positive

Predation Positive Negative

Competition Negative Negative

Mutualism

Commensalism

Parasitism Predation

Competition

Optimality

Which is the better eye?

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EVOLUTIONARY PROCESSES AND PATTERNS