Note:  we will cover material from pages 457-467 on Exam 2

Key requirements for evolutionary theory:
1. Must be able to explain how adaptations arise in populations: evolutionary processes Chapter 20
2. Must also explain macroevolution: the evolution of new species and larger taxonomic groups
 

Origin of new species occurs by two means:
Anagenesis: transformation of one species into another
Cladogenesis: budding of one or more species from parent form that remains extant
    (more common)
 
 
 

Biological species concept emphasizes reproductive isolation
Biological species = population or groups of populations whose members have the potential to
  interbreed in nature and to produce viable, fertile offspring
 - cannot produce viable offspring with other species
 - largest unit in which gene flow is possible

Morphological species - species are defined by measurable physical features useful for classifying both fossil & living forms

Still other ways to define species
 
 

Different types of reproductive barriers separate species
Reproductive barrier = any factor that impedes 2 species from hybridizing, reinforce
        genetic isolation

Prezygotic and Postzygotic barriers isolate the gene pools of biological species

Prezygotic barriers:  impede mating between species or hinder fertilization of the ova should mating occur

Postzygotic barriers:  prevent the hybrid zygote from developing into viable, fertile adults

Isolation arises from:
    1. Living in different habitats
    2. Temporal isolation
    3. Behavioral differences
    4. Mechanical features
    5. Gamete incompatibility
    6. Reduced hybrid viability or fertility

Reproductive barriers act to maintain genetic isolation between species:
Wood frogs & leopard frogs very similar, but are genetically
isolated by each species breeding during different periods

Speciation events are classified into 2 modes based on geographical relations
Allopatric speciation occurs when gene flow is blocked by the development of a geographical barrier
 1. Whenever populations are isolated gene pools accumulate   differences by microevolutionary processes
 2. Peripheral isolates at range edges may also diverge
 3. Considered the primary mode of macroevolution

Sympatric speciation is tbe formation of a new species within the range of the parent species
 1. Reproductive isolation evolves without isolation
 2. Reproductive barriers may arise quickly due to mutation
 Example:  polyploidy due to improper cell division can result in immediate    reproductive barriers; relatively common in plants
 

Grand Canyon: formed by combination of erosion by Colorado River
& uplifting of region over time
Illustrated by photo of Grand Canyon
 
 

Allopatric speciation is facilitated by geographical barriers that physically isolate populations,
which may then diverge over time

1. Geologic processes fragment populations
2. Differences between population isolates gradually accumulate
3. If barrier is removed populations may or may not be able to interbreed
 
 

Grand Canyon & Allopatric Speciation in Ground Squirrels
Illustrated by allopatric speciation in antelope ground squirrels
 
 

Sympatric speciation:  reproductive barriers can arise rapidly due to polyploidy
1. Sympatric speciation by polyploidy is more common in plants than animals

Autopolyploidy   vs   allopolyploidy
 (same species)        (different species)

Example in gray tree frogs
- tetraploid form resulted from hybridization between eastern and western gray tree frog populations