Speciation

Speciation• Speciation = formation of new species• Species = group of organisms that breed with

one another and produce fertile offspring in nature (share a common gene pool)

Speciation can happen in two modes

• Modes of speciation:– Sympatric: new

species develop in same geographic region• Sym= same

– Allopatric: new species develop in separate regions• allo= other

Isolation isn’t always bad…• As new species evolve, populations become

reproductively isolated from each other: When 2 populations cant breed and produce fertile offspring, resulting in separate gene pools– Behavioral isolation: Capable of breeding, but have

different courtship rituals or behaviors– Geographic isolation: Separate by geographic barriers– Temporal isolation: Reproduce at different times

Geographic Isolation (allopatric)

• Two populations are separated by geographic barriers. Over time different pressures result in distinct species– Rivers, mountains, bodies of water, glaciers, deserts

Behavioral Isolation

• Differences in the behavior of two populations prevent mating

• Because there is no gene exchange between populations, evolution occurs

• Behaviors:– Mating rituals– Mate preference– Mate calling

Behavioral Isolation (sympatric)

Temporal Isolation (sympatric)

• Two or more populations are separated by the time of year/day that reproduction occurs– Nocturnal vs Diurnal mating– Seasonal mating differences

Speciation can happen at two different rates

• Gradualism: Evolution occurs slowly, gradually and continuously

• Punctuated Equilibrium: Species remain unchanged for long periods of time. During certain events, species undergo rapid evolution.

• Both of the processes above have likely happened

Speciation of Darwin’s Finches• Speciation in the Galapagos finches occurred by:

– Founding a new population: A small population of finches migrates to a different island

– Geographic isolation: Finches don’t usually fly over open water, so stayed on own island (separate gene pool)

– Changes in the new population’s gene pool: Adapted to new environment (directional selection) to be more fit

– Reproductive isolation: Differences in phenotypes and mating rituals may turn different finches off to one another

– Ecological competition: Similar finches compete, so individuals that are most different from each other have the highest fitness, because less competition.

– Continued Evolution: Process repeats and over many generations, it produced the 13 different finch species