Species and Reproductive Isolation

Biological species concept

a group of individuals that

are capable of exchanging genetic

material through interbreeding to

produce fertile offspring

The biological species concept does

NOT apply to asexual or extinct

organisms

Cryptic species

similar in appearance, but

different species

Reproductive isolation

occurs in sexually reproducing

organisms when two individuals cannot merge their genes(pre zygotic or post zygotic)

Pre-zygotic

Act before fertilization to prevent

fertilization from happening

• What are mechanisms for pre-zygotic

isolation?

• Behavior/mate choice = individuals mate

based on specific courtship rituals, songs,

displays

• Gametic isolation = gametes of different

species do not recognize each other and

can’t interact appropriately

• Temporal isolation = separated in when

they mate

• Geographic/ecological isolation =

separated in where they mate

Post-zygotic

Act after fertilization and results

in failure of fertilized egg to

develop into fertile individual

• Fertilization is successful

• All caused by genetic

incompatibility  sterile adult or

inviable zygote

Models of speciation

Allopatric speciation: requires the

physical separation of two related

populations

• Most common

• Peripatric speciation: small peripheral

population becomes geographically

isolated

• Parapatric speciation: neighboring

populations (with overlapping

territories) diverge while maintaining

limited gene flow

• Sympatric speciation: establishment

of genetic incompatibilities without

physical separation