BILD 3 Lecture Notes - Lecture 10: Sympatric Speciation, Allele Frequency, Bild
13 Jun 2018
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BILD 3 Lecture 10
4/23/2018
• Evolutionary processes and speciation
o When populations stop interbreeding, divergence ensues
o Assuming no gene flow:
▪ Different mutations accumulate in each population
▪ Natural selection will change allele frequencies differently in each
population according to their environments
▪ Genetic drift will result in the fixation and loss of different alleles in each
population
• Mainly for smaller populations
o Mechanisms of fertilization evolves most quickly in species, which is why a
species that eoled o’t alays e ale to reed
• How species arrive: allopatric and sympatric speciation
• Allopatric speciation: physical isolation
o Other + fatherland
o Two species diverge from one another in physically different locations
o Reproductive isolation occurs because populations are geographically separate
o First method: vicariance
▪ Ancestral population existed prior to a geographic change that separated
populations
▪ Occurs when the divergence of two populations is due to a physical
barrier between the two (physical isolation)
▪ E.g. isthmus across Panama
• Hypothesis: if land bridge isolation populations of an ancestral
species, then for that species, their closest relative should be on
the other side of the barrier across the isthmus for a species of
shrimp. Closest relative is on the other side of the land mass, with
further speciation occurring on both the Pacific and Caribbean
sides
o Second method: dispersal
▪ The geography does’t hage, it’s the eers of the population that
move; movement of the animals divides the ancestral population
▪ Divergence of a small population away from an ancestral population
▪ E.g. geology of Hawaiian Islands
• Hawaiian Drosophila
o Adaptive radiation: speciation events lead to filtration of
e ihes as they’re fored ad the new populations of
flies are able to adapt to whatever the environment is
• Hypothesis: the initial population of flies inhabited the older
islands, and as the flies moved to other islands, they dispersed,
they went to the next nearest island and further speciate. Some
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