BI111 Lecture Notes - Lecture 8: Parapatric Speciation, Gene Flow, Speciation

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1 Feb 2017
BI111- Lecture 8 January 20th, 2017
How do new Species Arise?
Spontaneous vs. Gradual processes
Why and Where do they arise?
Allopatry, parapatry and sympatry
What keeps them isolated from each other?
Adaptation, drift and divergence
Allopatric Speciation (Space gives us opportunities for new species to arise)
Most common/uncontroversial way that sub-divided populations can speciate
Relies on geographic isolation (Alaska islands were raised up above normal levels- Fish
were captured in fresh water lakes rapidly and slowly)
o Gene flow is the great homogenizer- Makes two distinct groups result in the same
group because of the blending of genes
o Presence of a barrier could split population, and give species a chance to diverge
in their own direction
o Continental Drift- Responsible for large scale changes in biodiversity (Distance
allows separation, and so allows uniqueness to arise)
Secondary contact- Species may have diverged completely and then rejoin
but there might be mechanisms that prevent gene flow from occurring
If there is gene flow, then it will cause the species to rejoin and become
Squirrels separated by the Colorado river, became two distinct different
species morphologically, mating calls, and they are not interested in
mating with one another (don’t even recognize each other as the same
Fst value- How different are the values (genetic profiles)- Distance
determines whether there is genetic flow
New Uplifted Islands in Alaska
Found that lateral plate count was less in the fresh water environment compared to ocean
water- Fewer predators therefore they didn’t need as much energy invested to build the
protective plates
Freshwater fish were smaller because there was less to eat, or smaller things than in
ocean environments
All this phylogenetic differences evolved in 50years
Reproductive Isolating Mechanisms
Keeps genetic diversity because it prevents gene flow from occurring
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