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.
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
“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