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 SpeciesEastern meadowlark (left) and western meadowlark (right) aretwo different species even though they look alike. They arereproductively isolated.
Example of Behavioral BarrierBehavioral signal (dance, movement, pattern, etc.) is required formating. “Secret password.” For fun: search “blue-footed booby” inyoutube.
Modes of Speciation
Example of Allopatric Speciation A. harrisi A. leucurus
Speciation and Geographic Isolation
North American salamander: A Ring Species
Long-distance dispersal and adaptive radiation
Sympatric speciation by autopolyploidyPolyploidy – extra sets of chromosomesAutopolyploidy – extra sets of chromosomes derived from a single species(failure of meiosis). Ex: 2n becomes 4n and 4n self-fertilizes or mates withother 4ns.
AllopolyploidyContribution of two different species to apolyploid 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 proportionsduring 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 partsExample: Hox genes – position of body parts in animals
Hox mutations and the evolution of vertebrates Development of backbone Development of jaws and limbs