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Chapter 14- Origin of Species
• Adaptive radiation• Allopatric speciation• Behavioral isolation• Biological species concept• Ecological species concept• Gametic isolation• Genealogical species concept• Gradualist model• Habitat isolation• Hybrid breakdown• Hybrid inviability
• Hybrid sterility• Mechanical isolation• Morphological species concept• Polyploidy cells• Punctuated equilibrium• Reproductive barrier• Speciation• Sympatric speciation• Taxonomy• Temporal isolation
Something to remember:
• Most of the time evolution is gradual, sometimes though it can be observed over several generations
Speciation
• Evolution of a new species– Biological species concept-
population or group of populations whose members can interbreed and produce fertile offspring
• Ring species- forms a ring around geographic feature (may cause speciation)
Speciation con’t
– Morphological species concept- classify species by measureable phenotypic traits
– Genealogical species concept- defines species by a set of organisms with unique genetic history
– Ecological species concept- idendifies by ecological niche (role in env)
Reproductive barriers
• Keep species separate
• Can cause speciation– Ex: mosquitoes in London Underground
Prezygotic reproductive barriers
• Prevents mating• Temporal isolation- mating/flowering occurs at
different times/seasons• Habitat isolation- populations live in different
habitats and don’t meet• Behavioral isolation- no attraction between sexes• Mechanical isolation- genitalia structure/flowers
differs, prevents copulation• Gametic isolation- gametes die before uniting
Postzygotic reproductive barriers
• Prevents development of fertile adults• Hybrid inviability- zygotes fail to develop or reach
sexual maturity• Hybrid sterility- don’t produce functional gametes• Hybrid breakdown- offspring of hybrids are weak or
infertile
Geographic isolation
• Causes speciation• Allopatric speciation• Ex: lakes dry up into smaller lakes, fish can’t move from
one to another• Ring species sometime end up as new species• Occurs when gene pool changes to create a
reproductive barrier• More likely to happen in small, isolated pop’s
Geographic isolation con’t• Galapagos finches
• Adaptive radiation- evolution of many species from a common ancestor due to new environments
Sympatric speciation• Reproductive isolation develops and new species arise
without geographic separation– Widespread in plants
• Accident in meiosis produces cells with extra chromosome sets
• Polyploid cells- cells that has more than 2 sets of chromosomes
• 2n gametes can self-fertilize and produce a 4n plant• Production of a 4n cell is an instant speciation event,
because it now can’t reproduce with parent species– Ex: strawberries
• 2n gamete fused with 1n gamete produces 3n which is sterile b/c odd chromosomes can’t form homologous pairs
Sympatric speciation con’t
– Chemicals can be used to induce these errors to hybridize plants
• Ex: yield of wheat with resistance of rye
– Polyploid crops: oats, potatoes, bananas, peanuts, barley, plums, apples, sugarcane, coffee, wheat, cotton, strawberries
– 25-50% of plant species are polyploid
Tempo of speciation
Tempo of Speciation con’t
• Gradualist- populations evolve gradually as they become adapted to new environments– Very few fossil sequences show the steady
accumulation of small changes
• Punctuated equilibrium- long periods of little change with abrupt episodes of speciation
• * although evolution is jumpy when viewed as a whole its relatively steady