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