1 Campbell et al. Chpt. 24 The Origin of Species.

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Campbell et al. Chpt. 24

The Origin of Species

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Microevolution leads to changes leads to changes within populationswithin populations

Macroevolution leads to great phenotypic changes resulting in distinctive lineages

(e.g. species)

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• Diversity of life

• What is a species?

• How does speciation occur?

• Rate of evolution

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1. Diversity of Life

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Part of giant experiment called life


Cambrian Explosion (Burgess shell)

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Diversity increased over time…

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… with some interuptions

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Bushy tree

Evolution does not follow an inbuilt direction!

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“Hobbits” - human tree just got bushier still.Homo floresiensis from 18,000 years ago, 1m high

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Species = basic unit

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Species = basic unit

Speciation - rise of new species

Continuous lineage - informationpassed through genes

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• 1.4 million species described

• ca. 10 million estimated

• many extinct species

(about 90% of all species that ever lived are extinct)

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• 1.4 million species described

• ca. 10 million estimated

• many extinct species

Large diversity of species - speciation must be a common event

Understanding how this diversity arose is a central question in evolutionary biology

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2. Species Concepts

I. Morphological Species Concept

Species are similar in their appearance

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2. Species Concepts

I. Morphological Species Concept - sometimes hard to apply

Two different species One single species

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2. Species Concepts

I. Morphological Species Concept - sometimes gets it wrong

New Zealand moa (extinct): females much bigger than males

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2. Species Concepts

II. Biological Species Concept

Two individuals of the same species interbreed withanother in the wild and produce viable and fertile young

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2. Species Concepts

II. Biological Species Concept - problems

•Fossils - how do we know if they interbreed?

•“Good” species can sometimes produce hybrid

•Asexual organisms

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2. Species Concepts

II. Biological Species Concept - problems

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2. Species Concepts

III. Cohesion Species Concept

Adaptive landscape

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2. Species Concepts

IV. Phylogenetic Species Concept

Species = lineage between successive speciation events

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3. Speciation

Process of speciation

Parentspecies

I. Barrier

2 separate species

III. Don’t interbreedII. Diverge

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3. Speciation

I. Establishing a barrier

• Geographical separation

• Breed at different times

• Different courtship display

• etc

Species are prevented from mating with each other- pre-zygotic barriers

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3. Speciation

II. Population divergence

Can be caused by any of the 5 causes ofevolutionExample: Artificial selection of domesticated animals

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3. Speciation


Example: Ring species Herring/Lesser Black-backed Gull

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3. Speciation


Genetic subdivisionExample: Mice on Madeira

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3. Speciation

III. Sexual incompatibility

Offspring from matings between groupsare not viable or fertile- post-zygotic barriers

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1. Barrier

3. Speciation

Example Picture-winged fruit fly (Rhagoletis)

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3. Speciation

Example Picture-winged fruit fly (Rhagoletis)

Witnessed speciation!

1. Barrier2. Divergence3. Don’t interbreed

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4. Rate of Evolution

• Gradualism (Darwin) - steady accumulation of small changes over long periods of time

• Rapid bursts of fast changes

• Stasis - no changes over long periods of time

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Example: Radiolaria

Punctuated Equilibrium (Eldrige & Gould) - long periods of stasis interrupted by short periods of rapid change

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Can speciation events be replicated?

Play again the tape

THE END

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2. Species Concepts

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Example: Radiation of Darwin Finches on Galapagos

1 Campbell et al. Chpt. 24 The Origin of Species.

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