Speciation 2. Postzygotic reproductive isolation Barriers in allopatric speciation Haldane’s rule Sympatric speciation. Another case of prezygotic reproductive isolation: Mimulus flowers and and pollinators.
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for aquatic species!
"When in the F1 offspring of two different animal races one sex is absent, rare, or sterile, that sex is the heterozygous [heterogametic] sex.
J.B.S. Haldane (1922) Sex-ratio and unisexual sterility in hybrid animals. J. Genetics12, 101-109.
In most familiar species except birds and butterflies the heterogametic sex is male
It turns out that the X chromosome is often implicated in hybrid sterility.
- females from D. persimilis x D. pseusoobscura F1
- males D. pseudoobscura.
Sympatric speciation is a controversial topic! Read e.g.
Futuyma: Evolutionary Biology, on this subject
Theodosius Dobzhansky, 1960s
Clarkia lingulata, 2n=18,
drier habitats, restricted range
Clarkia biloba, 2n=16, (ancestral number) wetter habitats, widespread
The hippocampus“The mermaid” by JW Waterhouse 1849-1917The Centaur