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W her e do new species come fr om? BIO101 Fall 2011 Key Terms: Speciation Species Hybrid Biological species concept Morphological species concept Ecological species concept Phylogenetic species concept Reproductive Isolation Prezygotic Isolation Postzygotic Isolation Hybrid Zone Allopatric Speciation Sympatric Speciation Punctuated Equilibria Key Questions: • What is a species? • How do allopatric and sympatric speciation differ? Are these differences important? • Why is geographic isolation not the same as reproductive isolation? Which is more important for speciation to happen? Lecture Outline: What is a Species? (note that’s both singular and plural). Most widely used definition is from Ernst Mayr in 1942; Biological Species Concept species is a group of populations with the potential to interbreed which would yield healthy and fertile offspring For a new species to form, must have reproductive isolation or some way to limit gene flow Barriers can be broadly classified to prezygotic and postzygotic Prezygotic includes Habitat Isolation Temporal Isolation Behavioral Isolation Mechanical Isolation Genetic Isolation Postzygotic inclues Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown Other species definitions Morphologcial Species Concept – species based on morphology Ecological Species Concept – species is based on the niche occupied Phylogenetic Species Concept –smallest group of individuals with a single common ancestor Allopatric speciation gene flow interrupted by a geographic barrier to yield 2 populations separation is only the first step – divergence later to yield a reproductive barrier Sympatric speciation is much less common. Still need some way to block gene flow as a repro barrier What if new species still have some contact? May lead to a Hybrid Zone, which can be very instructive Hybrid zones over time can lead to Reinforcement of barriers, Fusion of species or Stable mainenance Punctuated equilibria – long times of no change followed by rapid change in fossil record Gradual – slow changes with many intermediates reproductive isolation can be caused by a single gene difference, if it makes a very strong barrier more common to have a few barriers each affected by a few genes