Download Speciation – Chapter 24 | Date: Changing Environments Accelerate

Speciation – Chapter 24 | Date:
Changing Environments Accelerate Evolution
 Evolution is always occurring

o
Antibiotic resistance
o
Antiviral resistance
o
Vaccines
New habitats = evolution
o
Adaptive radiation
Species
 Definition
o

Reproductive isolation
Speciation: formation of new species
o Allopatric speciation
 Geographic barrier (physical separation)

Common barriers

Diverging gene frequencies

o

Natural selection

Mutation

Genetic drift
Results in reproductive barrier and new species
Sympatric speciation
 No geographic barrier – genetic difference instead

Occurs via…
 Balanced polymorphism
o Example: color and camouflage in insects

Polyploidy
o Nondisjunction
o

Normal in plants
Hybridization (parapatric speciation)
o Hybrid zone
o
May cause

Reduced hybrid viability
o

Hybrid breakdown
Hybrid genetic variation may be greater than either parent
Example: snakes
Example: fireflies
Temporal isolation
o Refers to time
o


Behavioral isolation
o Example: sticklebacks
o

Reduced hybrid fertility
Habitat isolation
o Two organisms live in same area, but rarely encounter each other
o


Example: flowering plants and temperature
Reproductive isolation
o Prezygotic barriers (mechanical isolation)

o
o
Postzygotic barriers (gametic isolation)

Reduced hybrid viability

Reduced hybrid fertility

Hybrid breakdown
Adaptive radiation
 Rapid evolution from single ancestor

Examples
 Australian marsupials


o
Temporal, behavioral, mechanical, gamete/genetic, and habitat isolation
Darwin’s finches
Mass extinctions

Normal

Most species go extinct, but new ones survive
Rate of speciation

Fossil record – incomplete or accurate?

Punctuated equilibrium

Gradualism