Western mates in winter
Australian fruit flies
D. Tyrone copulates at sundown
D. Neohumeralis copulayes from mid morning to mid afternoon
Not always. External fertilization
Insects. Lock and key sturcture
Chemical recognition is important
Immunological barriers exist
Genetic incompatibility is important cause.
Generally aborts before development is complete.
Sometimes development proceeds, but resulting organism is not healthy
Parents of hybrid may have different chromosome number or structure.
Hybrid may be poorly adapted to obtain food,escape predators.
Hybrid may not be sexy!
There is normally of alleles between these populations (gene flow)
Populations are isolated geographically
Once isolated RIMs can arise over time. Populations diverge
Lake Malawi in africa- Chichlids
Lake Bonneville death valley-pupfish
Hawaii, south pacific, Madagascar.
Reproductive barriers arise within the range of one species/population
Less common than allopatric. More examples from plants due to autopolyploid:chromosome number doubles instantly
1 larvae develop on fruit
2 adults mate, deposit eggs on host plant.
1860s discovered on apples. Different fruiting time. Temporal isolation.
1960s discovered on cherries. Different fruiting time. Temporal isolation
Selection varies. Different alleles are favored at different points
Horizontal gene flow is reduced.
Reduction in gene flow may be enough to allow speciation
A hybrid zone may be present. Orioles
Sycamores in North American and Europe=30 million years. Hybrids are still fertile.
Faroe island house mouse-250 years.
Drosophilia paulistorum- few years in lab
Important evolutionary changes occur over relatively “short” periods of time when populations begin to diverge. Long periods of stasis