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: IT IS NOT EXPLAINABLE BY ANY OTHER CONCEPT." 

It is also ironic that in a land filled with examples of convergent 
evolution (numbats, flying phalangers, marsupial moles) that people can be 
so fundamentally ignorant.

Dave.

 

 * WinQwk 2.0 a#595 * KILL THE WABBIT!