Eological/Habitat isolation

Temporal isolationAnimals that breed at different times of the year will not produce offspring
Example of temporal isolationWestern and eastern spotted skunk. Eastern mates in summer
Western mates in winter
Australian fruit flies
D. Tyrone copulates at sundown
D. Neohumeralis copulayes from mid morning to mid afternoon
Mechanical isolationMale and female anatomy must be compatible for successful mating to occur.
Not always. External fertilization

Insects. Lock and key sturcture

Ex of mechanical isolationOlithreutes olivaceana
Olithreutes concinnana
Gametic isolationSperm from one species rarely fertilizes an egg from a different species.

Chemical recognition is important

Immunological barriers exist

Postzygotic RIMsPrevent zygote from developing into vkable, fertile adult
Hybrid inviability or mortalityFailure of zygote to develop appropriately.
Genetic incompatibility is important cause.

Generally aborts before development is complete.

Sometimes development proceeds, but resulting organism is not healthy

Hybrid infertility/ reduced viabilityProblems arise in meiosis if chromosomes cannot pair properly.
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!

Example of hybrid infertility/ reduced viabilityMule and liger (male lion female tiger)
Gene flowSpecies consists

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of discrete, separate populations.
There is normally of alleles between these populations (gene flow)
In the absence of gene flow RIMs can arise. How?Mutations
Genetic drift
Allopatric speciationMeans “other homeland”
Populations are isolated geographically
What barrier forms in allopatric speciation?Geographic.(like a mountain) Separating species into 2 or more isolated groups.
Once isolated RIMs can arise over time. Populations diverge
Allopatric speciationLakes in times of drying
Lake Malawi in africa- Chichlids
Lake Bonneville death valley-pupfish
Sibling speciesOnce one species but have became 2 overtime
Allopatric speciation on islandsMany unique species on islands.
Hawaii, south pacific, Madagascar.
Endemic speicesOccur nowhere else
Are island chains active sites for sleciation?Yes
Sympatric speciationOccurs without geographic isolation.
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
Rhagoletis pomonella-apple maggot flyNative host is Hawthorne tree. Life cycle:
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
Orcas and sympatric speciation?
Parapatric speciationSpeciation that occurs among populations distributed along a cline.
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
ClineEnvironmental gradient. Gene flow occurs across gradient.
How rapid is speciation?Isthmus of Panama= 3million years +or-
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
GradualismEvolution proceeds as an accumulation of small changes over very long period of time
Punctuated equilibrium1972. S.j. Gould and N. Eldredge.
Important evolutionary changes occur over relatively “short” periods of time when populations begin to diverge. Long periods of stasis
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