The story of rabbits in Australia

The story of rabbits in Australia ia another fascinating case history in evolutionary biology. Rabbits are not native to Australia. Before their introduction, the ecological niche was filled by a great variety of small kangaroos called wallabies. In 1859, 12 wild rabbits, Oryctolagus cuniculus, were imported from England. By 1886 their descendents were colonizing new areas of southeastern Australia at the rate of 66 miles a year in all directions. By 1907 the rabbits had reached both the west and the east coasts of Australia, roughly the distance between California and New York. Nothing could stop the plague of rabbits. Thousands of miles of "rabbit-proof fences" failed to stem the tide. Certainly the wallabies offered no competitive resistance, and the few native predators made scarcely a dent in the rabbit populations. Hunting, trapping, and poisoning were to no avail. The rabbits were eating much of the sparse vegetation that supported Australia's huge sheep and cattle industry, and the graziers were suffering enormous financial losses. The only solution was biological control. After much testing, government biologists introduced a mosquito-borne virus called myxomatosis. This virus caused a nonlethal disease in its natural host, but the disease was deadly for the European rabbit and completely harmless to all other Australian wildlife, domestic animals, and humans. To all indications, the solution had been found. The disease did indeed take hold in 1950, and by 1952 it had produced a nationwide epidemic in the rabbit population. The mortality rate reached 99.9%, BUT A GOOD EVOLUTIONARY BIOLOGIST COULD PREDICT WHAT WOULD HAPPEN NEXT. A parasite that invariably kills its hosts before ensuring its own survival would be selected against (all of its individuals would die). And that is what inevitably happened to the myxomatosis disease. The viruses had been randomly mutating, and the mutations that produced less virulence were selected (because the more virulent strains died with their hosts). The rabbits, too were mutating, and they were being selected for greater resistance to the disease. The result was a milder disease and stronger rabbits-therefore more rabbits. Today the mortality rate is down to 40 percent. There are still annual outbreaks of myxomatosis in Australia, but the disease is less effective in controlling the rabbits. This is evolution in action, instigated by humans, and occuring through natural evolutionary forces: 

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