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The Origin of Species
Chapter 24Chapter 24
BCOR 012BCOR 012
Jan. 31 and Feb. 2, Jan. 31 and Feb. 2, 20112011
Outline for January 31, Feb. 2, 2011:
I. IntroductionII. What is a species?
The biological species conceptReproductive isolating mechanismsAlternative species concepts
III. Modes of speciationAllopatricSympatricthe tempo of change
The Biological Species Concept
The biological species concept defines a species as a population or a series of populations whose members have the potential to interbreed and which are reproductively isolated from other such populations.
Limitations of the BSC:
• Not applicable to asexually reproducing organisms
• Useless with respect to the fossil record
Alternative species concepts:
• Ecological species concept - defines a species in terms of its ecological niche
• Morphological species concept - emphasis is on unique structural features
• Phylogenetic species concept - emphasis is on ancestor-descendent relationships
• Pluralistic species concept - acknowledges that, where species concepts are concerned, one size may not fit all!
There are two general modes of speciation:
• Allopatric (other homeland)- speciation takes place in populations with geographically separate ranges
• Sympatric (same homeland) - speciation takes place in geographically overlapping populations
S N
Ammospermophilus harrisi Ammospermophilus leucurus
Allopatric speciation of antelope squirrels in the Grand Canyon
In In allopatric speciationallopatric speciation, a new species originates while geographically isolated from its ancestor. As the new species evolves by genetic drift and natural selection, reproductive isolation from the ancestralspecies may evolve as a by-product of genetic change.
Sympatric speciation - a mode in which a new species arises in thegeographic midst of its progenitorspecies.
Copper-tolerant Mimulus guttatus
In plants, sympatric species may arise by polyploidya condition that results in extra sets of chromosomes
in the derivative species.
An example from the European holly ferns ….
The origin of European Polystichum aculeatum
P. aculeatum
P. setiferum P. lonchitisprimary diploid
hybrid(2X)
(4X)
(2X)
The origin of European Polystichum aculeatum
P. aculeatum
P. setiferum P. lonchitisprimary diploid
hybridP. setiferum n=41
Pundamilia pundamilia
a) Normal light
b) Monochromatic orange light
Non-random mating, in which females select mates having a preferred appearance, is the main reproductive barrier keeping these two species separate in nature. This is an example of sympatric speciationsympatric speciation in response to sexual selection.
Pundamilia nyererei
Sympatric speciationSympatric speciation requires the emergence of some sort of reproductive barrier that isolates the gene pool of a population subset without geographic separation from the parent population.
Darwin’s original idea was that
species diverge gradually.
More recently, the idea that there are rapid speciation events
interrupting periods of no change has become
popular.
Punctuated equilibria vs. gradual divergence
http://evolution.berkeley.edu/evosite/evo101/VIIA1bPunctuated.shtml
http://evolution.berkeley.edu/evosite/evo101/VIIA1bPunctuated.shtml
Punctuated equilibria vs. gradual divergence
Pollinator shifts drive increasingly long nectar spurs in columbine flowers. Whittall and Hodges, 2007 ---- Nature 447: 706-710.