Two strains of
Drosophila paulistorum developed hybrid sterility of male offspring between 1958 and 1963. Artificial selection induced strong intra-strain mating preferences. (Test for speciation: sterile offspring and lack of interbreeding affinity.)
Dobzhansky, Th., and O. Pavlovsky, 1971. "An experimentally created incipient species of Drosophila",
Nature 23:289-292.
Evidence that a species of fireweed formed by doubling of the chromosome count, from the original stock. (Note that polyploids are generally considered to be a separate "race" of the same species as the original stock, but they do meet the criteria which you suggested.)
(Test for speciation: cannot produce offspring with the original stock.)
Mosquin, T., 1967. "Evidence for autopolyploidy in
Epilobium angustifolium (Onaagraceae)",
Evolution 21:713-719
Rapid speciation of the Faeroe Island house mouse, which occurred in less than 250 years after man brought the creature to the island.
(Test for speciation in this case is based on morphology. It is unlikely that forced breeding experiments have been performed with the parent stock.)
Stanley, S., 1979.
Macroevolution: Pattern and Process, San Francisco, W.H. Freeman and Company. p. 41
"Three species of wildflowers called goatsbeards were introduced to the United States from Europe shortly after the turn of the century. Within a few decades their populations expanded and began to encounter one another in the American West. Whenever mixed populations occurred, the specied interbred (hybridizing) producing sterile hybrid offspring. Suddenly, in the late forties two new species of goatsbeard appeared near Pullman, Washington. Although the new species were similar in appearance to the hybrids, they produced fertile offspring. The evolutionary process had created a separate species that could reproduce but not mate with the goatsbeard plants from which it had evolved."
The article is on page 22 of the February, 1989 issue of
Scientific American. It's called "A Breed Apart." It tells about studies conducted on a fruit fly,
Rhagoletis pomonella, that is a parasite of the hawthorn tree and its fruit, which is commonly called the thorn apple. About 150 years ago, some of these flies began infesting apple trees, as well. The flies feed and breed on either apples or thorn apples, but not both.
There's enough evidence to convince the scientific investigators that they're witnessing speciation in action. Note that some of the investigators set out to prove that speciation was not happening; the evidence convinced them otherwise.
