The Origin of Species

24.2

Speciation can take place with or without geographic

separation24.2

Recall: Speciation The formation of a new species Reproductive isolation is key

2 Modes of Speciation (a) Allopatric (b) Sympatric

Allopatric Speciation “Other country” Geographically isolated populations Separated gene pools diverge as mutations,

natural selection events occur within each population

Eventual reproductive isolation Example: fruit flies and food medium

Sympatric Speciation “Same country” Speciation occurs within populations Some kind of reproductive barrier isolates

members of the population Examples: polyploidy, habitat differentiation,

sexual selection

Polyploidy Extra sets of chromosomes in cells More common in plants

Habitat Differentiation Genetic factors enable a

subpopulation to utilize a habitat/resources the parent species cannot

Example: apple maggot flies Parent species a pest of

hawthorn fruit Subspecies began laying eggs

in apples which mature faster Temporal isolation developed

Hawthorn flies develop more slowly than apple maggot flies

Sexual Selection Females select mates based on

appearance Example: cichlids