From Biol301

Contents 1 Speciation 1.1 Allopatric Speciation 1.1.1 Founder Effect Speciation (dispersal and colonization) 1.1.2 Vicariant Speciation (large geographic split) 1.1.3 Biological Mechanisms of Allopatric Speciation 1.2 Sympatric Selection 1.2.1 Polyploid Speciation 1.2.2 Ecological Speciation

Speciation

• not special, same mechanisms as we learned from Freeland; there's nothing crazy going on here with speciation
• Hard for us to understand because it takes so long but it's not different than the way a physicist understands the speed of light.

Allopatric Speciation

• allo = other, patric = domain.
• Divergence is caused by geographic separation
• 90 - 99% of speciation is by allopatric speciation
• 1942 - Earnst Mayr: solved the problem of how species originate
• 2 scenarios for allopatric speciation: founder effect speciation and vicariant speciation

Founder Effect Speciation (dispersal and colonization)

• exactly which organism(s) colonizes is important (which alleles they carry)
• Example: mallards were blown out to Hawaii

Vicariant Speciation (large geographic split)

• vicariously: riding along
• Example: lungfish riding South America and Africa as they split from Pangea
• Example: Canyon forming separated squirrels, spurce, etc.
• Example: River forming oxbow lake.
• Exmaple: Formation of Isthmus of Panama (one man's bridge is another's barrier)

Biological Mechanisms of Allopatric Speciation

1. Natural Selection (predation as an example)
2. Genetic Drift (more important for founder effect speciation)
3. Mutations (since they are random, a mutation may occur in one split population that does not occur in another)
4. Sexual Selection (pretty darn important)

Sympatric Selection

• sym = same, patric = domain.
• Divergence in the absence of barriers.
• 2 scenarios for sympatric speciation: polyploid speciation and ecological speciation

Polyploid Speciation

• Example:
  • Grey tree frog has two species in the Eastern US: one is diploid (2n=24) and one is tetraploid (4n=48)
  • Diploid and tetraploid cannot interbreed (or at least they don't produce viable offspring)
  • There is no morphological or genetic difference (other than number of copies of chromosomes, obviously)
• Polyploid speciation is very important in plants, probably because they can (facultatively) self fertilize and are therefore more likely to be able to start a population of a polyploid mutants.

Ecological Speciation

• Cuased by natural selection
• Example: stickleback fish has two species: a deep water (smaller, more streamlined) version and a shallow water (larger, slower, more bulky) version.