BIO 370 Chapter Notes - Chapter 19: Yellowstone Lake, Hybrid Zone, Parapatric Speciation
An example of Progenitor- Derivative species pair.
PHENETIC SPECIES
S. yellowstonensis and S. niagarae are good phenetic species.
PHYLOGENETIC SPECIES
S. yellowstonensis is a good phylogenetic species (with several autapomorphies) S. niagarae not
so much.
BIOLOGICAL SPECIES
Indirect evidence that they are good biological species. S. niagarae almost certainly is regularly
dispersed into Yellowstone Lake.
S.niagarae
slope
S. yellowstonensis
slope
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Parapatric Speciation
When two adjacent pops diverge into separate species without geographic barrier to dispersal.
(Para – next to, beside, near)
A hybrid zone is essential in the parapatric speciation process. By contrast, allopatric and
sympatric models do not include a hybrid zone during the speciation process.
The ends of the gradient select for different homozygotes.
In most parapatric speciation models, it is assumed that the hybrid zone between populations
will eventually disappear, completing the speciation process.
Why would this be the case?
The implicit assumption is that hybrids are
at a disadvantage.
However, not all parapatric models assume that hybrid individuals are at a disadvantage.
One model assumes a genotype-by-environment interaction such that in hybrid zones hybrids
may have superior fitness to nonhybrids.
A case in point involves studies of big sagebrush (Artemesia tridentata) from the western US.
Two subspecies of Artemesia tridentata hybridize in the Wasatch Mountains of Utah. One,
subsp. tridentata, is found at low elevations; the other, subsp. vaseyana, grows at high
elevations.
The two subspecies hybridize where they make contact at intermediate elevations.
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Document Summary
Phenetic species: yellowstonensis and s. niagarae are good phenetic species. Phylogenetic species: yellowstonensis is a good phylogenetic species (with several autapomorphies) s. niagarae not so much. Indirect evidence that they are good biological species. S. niagarae almost certainly is regularly dispersed into yellowstone lake. When two adjacent pops diverge into separate species without geographic barrier to dispersal. (para next to, beside, near) A hybrid zone is essential in the parapatric speciation process. By contrast, allopatric and sympatric models do not include a hybrid zone during the speciation process. The ends of the gradient select for different homozygotes. In most parapatric speciation models, it is assumed that the hybrid zone between populations will eventually disappear, completing the speciation process. The implicit assumption is that hybrids are at a disadvantage. However, not all parapatric models assume that hybrid individuals are at a disadvantage. One model assumes a genotype-by-environment interaction such that in hybrid zones hybrids may have superior fitness to nonhybrids.
