Download W her e do new species come fr om?

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