Ch.24 origin of species
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Transcript of Ch.24 origin of species
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ORIGIN OF SPECIES
Chapter 24
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Speciation• Speciation - Origin of
new species
• Two models:– Anagenesis– Cladogenesis
• Micro v. Macro evolution– Micro – changes within a
population/ species– Macro – origin of new
species, genera, etc.
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What is a species?• Hard to define, considers
– Morphology– Body function– Biochemistry– Behavior– Genetics
• Biological species – Reproductive isolation– Can produce viable, fertile offspring
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Biological Species
Eastern meadowlark (left) and western meadowlark (right) are two different species even though they look alike. They are reproductively isolated.
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Barriers to Reproduction
• Prezygotic – prevent fertilization
• Postzygotic – prevent viable, fertile offspring
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Example of Behavioral Barrier
Behavioral signal (dance, movement, pattern, etc.) is required for mating. “Secret password.” For fun: search “blue-footed booby” in youtube.
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Modes of Speciation
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Example of Allopatric SpeciationA. harrisi A. leucurus
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Speciation and Geographic Isolation
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North American salamander: A Ring Species
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Adaptive Radiation
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Long-distance dispersal and adaptive radiation
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Sympatric speciation by autopolyploidyPolyploidy – extra sets of chromosomes
Autopolyploidy – extra sets of chromosomes derived from a single species (failure of meiosis). Ex: 2n becomes 4n and 4n self-fertilizes or mates with other 4ns.
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Allopolyploidy
Contribution of two different species to a polyploid hybrid
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Models for the tempo of speciation
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“Evo-Devo”• Evolutionary Biology meets Development
– Slight genetic divergence can become major difference between species
• Genes that involve– Rate of development– Timing– Spatial patterns
• Keywords involved– Allometric growth– Heterochrony– Paedomorphosis– Homeotic genes
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Allometric GrowthDifferent rates of growth – alter body proportions during development
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Heterochrony•Different timing•Modification in allometric growth
•Example: Salamander feet – •a - longer time for foot development – longer digits and less webbing•b – less time for foot development – shorter digits, more webbing – adaptation for gripping tree
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PaedomorphosisAdult stage of species retains juvenile characteristics
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Homeotic GenesDetermine placement of body parts
Example: Hox genes – position of body parts in animals
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Hox mutations and the evolution of vertebrates
Development of backbone
Development of jaws and limbs
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Species Selection