Speciation

1
Speciation Rates of Evolution
AP Biology Unit 4
2
Speciation

• A species is a population or group of populations
  that
• Members can mate with one another to produce
  viable, fertile offspring
• Cannot produce fertile, viable offspring with
  other populations

3
Reproductive isolation

• Species are usually reproductively isolated from
  one another (have limits to reproduction or lead
  to offspring of fitness 0)
• Prezygotic barriers -- before the zygote
• Postzygotic barriers after the zygote

4
Prezygotic barriers

• These are things that prevent mating or
  fertilization even if mating occurs

5
Prezygotic Barriers

• Habitat Isolation
• Species live in different habitats and dont meet
  much (if at all)
• Temporal Isolation
• Mating occurs at different times
• Behavioral Isolation
• Mating behavior differs between species
• Mechanical Isolation
• Body parts arent able to match up (even in
  plants)
• Gametic Isolation
• Sperm from one species is not able to fertilize
  the egg from another species

6
One example Behavioral Isolation

• Blue footed boobies engage in a courtship display
  in which the male high steps to draw attention
  show off his feet to the female
• They also fly over the females heads to flash
  their feet

Image taken without permission from
http//z.about.com/d/animals/1/0/h/9/shutterstock_
304958.jpg
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Postzygotic barriers

• These are things that prevent the offspring from
  being viable or fertile

8
Postzygotic barriers

• Reduced Hybrid viability
• Genes from different species interact and prevent
  or impair development
• Reduced Hybrid fertility
• Meiosis in hybrids cant produce gametes since
  chromosomes are different
• Hybrid breakdown
• When hybrids mate their offspring are sterile or
  frail

9
Allopatric vs. Sympatric Speciation

• Allopatric speciation
• Speciation occurs as a result of goegraphic
  isolation
• Sympatric speciation
• Speciation occurs without geographic isolation

10
Polyploidy

• Polyploidy having too many chromosomes
• In plants, errors in cell division may result in
  polyploid individuals who are reproductively
  isolated from the parent species

11
Polyploidy

• In other cases, sometimes a fertile hybrid can
  also result (allopolyploid)

12
Booming Diversity

• Adaptive radiation can occur when there is sudden
  opportunity in the environment
• extinction of a competitor, parasite, or predator
  
• Mammal adaptive radiation after extinction of
  dinosaurs
• genetic drift (specifically founder effect)
• Plant adaptive radiation when they arrived on
  Hawaiian Islands

13
Rates of Evolution

• Biologists also are interested in the rate of
  evolution
• Is it happening at a slow steady speed?
• Or is it happening in bursts?
• There are 2 proposed models

14
Gradualism

• Model that says evolution is occurring at a
  constant, steady rate

15
Punctuated Equilibrium

• Periods of a lots of evolution (speciation)
  followed by periods with no noticeable evolution
• Spurts of evolution
• Which is correct? Probably a mixture of the 2.