Dwain Clement, 38, was driving home one night in 1998 along Interstate 318 in Minnesota when his car gave a jolt as though it had struck some object in the road. Dwain checked for damage, and then walked back to see what he had hit. He was surprised to see a small object moving across the road in regular spurts of a few inches at a time: he was astonished, when he picked it up, to find what was clearly a frog inside a shell like that of a tortoise. He put it back on the road and watched it, apparently unharmed, finish its journey across the highway and into the field, propelling itself by thrusts of its hind legs which gained it about six inches each time.
When he wrote a letter describing his find to the local newspaper, the Thief River Falls Monitor, a number of other readers wrote in giving similar accounts dating back to 1995. According to a local naturalist, Interstate 318 had been built across a migrating route used by amphibians going to the marshes during the breeding season to spawn, and there had been a high mortality rate amongst the local frogs and toads when the road first appeared at the beginning of the century. Despite several later reports, no examples of the armoured frogs have yet been examined by herpetologists.
This account of what is locally known as the ‘Panzer Frog’ raises interesting questions for evolutionary biologists. Are we seeing the expression of genes which have been silent in amphibians since the Carboniferous era, or is there an even more remarkable possibility? It is significant that the frog seen by Dwain Clement was able to finish its journey after an encounter with a car that would have reduced an ordinary frog to a green stain on the road. Is it possible that the death rate after the building of the road imposed massive evolutionary pressures on the frog population, so great that the benefit conferred by armour during this one perilous crossing outweighed its obvious drawbacks during the rest of the animal’s life? If so, it represents a remarkable instance of evolution producing major change in less than 100 years, and probably the first example of the motor-car affecting the evolution of a vertebrate.
When he wrote a letter describing his find to the local newspaper, the Thief River Falls Monitor, a number of other readers wrote in giving similar accounts dating back to 1995. According to a local naturalist, Interstate 318 had been built across a migrating route used by amphibians going to the marshes during the breeding season to spawn, and there had been a high mortality rate amongst the local frogs and toads when the road first appeared at the beginning of the century. Despite several later reports, no examples of the armoured frogs have yet been examined by herpetologists.
This account of what is locally known as the ‘Panzer Frog’ raises interesting questions for evolutionary biologists. Are we seeing the expression of genes which have been silent in amphibians since the Carboniferous era, or is there an even more remarkable possibility? It is significant that the frog seen by Dwain Clement was able to finish its journey after an encounter with a car that would have reduced an ordinary frog to a green stain on the road. Is it possible that the death rate after the building of the road imposed massive evolutionary pressures on the frog population, so great that the benefit conferred by armour during this one perilous crossing outweighed its obvious drawbacks during the rest of the animal’s life? If so, it represents a remarkable instance of evolution producing major change in less than 100 years, and probably the first example of the motor-car affecting the evolution of a vertebrate.
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