Lecture 5

Lecture 5 - Geography of speciation Classical debate in...

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Geography of speciation Classical debate in evolutionary biology: Can speciation happen without geographic isolation occurring at some point? It can be hard to completely rule out the role of geographic isolation in the early stages of reproductive isolation.
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Geography of speciation Classical debate in evolutionary biology: Can speciation happen without geographic isolation occurring at some point? It can be hard to completely rule out the role of geographic isolation in the early stages of reproductive isolation. When speciation happens without any geographic separation, we refer to this as sympatric speciation. Ernst Mayr didn’t buy into this…
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Ernst Mayr on sympatric speciation (1963) “One would think that it should no longer be necessary to devote much time to this topic, but past experience permits one to predict with confidence that the issue will be raised again at regular intervals. Sympatric speciation is like the Lernaean Hydra which grew two new heads whenever one of its old heads was cut off.”
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Geography of speciation Classical debate in evolutionary biology: Can speciation happen without geographic isolation occurring at some point? It can be hard to completely rule out the role of geographic isolation in the early stages of reproductive isolation. When speciation happens without any geographic separation, we refer to this as sympatric speciation. Ernst Mayr didn’t buy into this… But it CAN happen (how frequently it happens is still debated)
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Examples of sympatric speciation Instantaneous complete speciation can happen via polyploid speciation (chromosome duplications) Happens in plants… very rarely (if ever?) does it happen in animals e.g. Error in cell division causes 2n gametes instead of 1n Long-term disruptive selection (?) Strong divergent ecological selection Adaptation to different habitats can make populations diverge In contrast, gene flow can make populations less different… So selection must be very strong in order to combat the effects of homogenization due to interbreeding!
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Adaptive radiations and rates of speciation Some evolutionary lineages have a LOT more species than others. Why??? “Adaptive radiations”
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Lecture 5 - Geography of speciation Classical debate in...

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