Ch.24 origin of species

ORIGIN OF SPECIES

Chapter 24

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.

What is a species?• Hard to define, considers

– Morphology– Body function– Biochemistry– Behavior– Genetics

• Biological species – Reproductive isolation– Can produce viable, fertile offspring

Biological Species

Eastern meadowlark (left) and western meadowlark (right) are two different species even though they look alike. They are reproductively isolated.

Barriers to Reproduction

• Prezygotic – prevent fertilization

• Postzygotic – prevent viable, fertile offspring

Example of Behavioral Barrier

Behavioral signal (dance, movement, pattern, etc.) is required for mating. “Secret password.” For fun: search “blue-footed booby” in youtube.

Modes of Speciation

Example of Allopatric SpeciationA. harrisi A. leucurus

Speciation and Geographic Isolation

North American salamander: A Ring Species

Adaptive Radiation

Long-distance dispersal and adaptive radiation

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.

Allopolyploidy

Contribution of two different species to a polyploid hybrid

Models for the tempo of speciation

“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

Allometric GrowthDifferent rates of growth – alter body proportions during development

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

PaedomorphosisAdult stage of species retains juvenile characteristics

Homeotic GenesDetermine placement of body parts

Example: Hox genes – position of body parts in animals

Hox mutations and the evolution of vertebrates

Development of backbone

Development of jaws and limbs

Species Selection