This kind of study, which was funded by the Natural Environment Research Council, has previously not been possible because although fossils preserve direct evidence of evolutionary change over thousands and millions of years, working out exactly what a long-dead fossil animal was eating when it was alive, and establishing a link between feeding and evolution, is very difficult.
The stickleback tooth chips and scratches were formed 10 million years ago as part of the normal process of tooth wear while the fish were alive and feeding in a large lake in what is now Nevada. “Like footprints in sand, the wear on teeth preserves a trail of evidence of how a fish feeds and what it feeds on,” says Dr Mark Purnell from the University of Leicester, lead author on the report. “The difficult bit was learning how to read that trail.”
The research team, based at the universities of Leicester, UK, and Stony Brook, USA, captured living stickleback (of the common or garden pond variety), fed them different kinds of food in different conditions and then examined their teeth using a powerful electron microscope. The team also looked at the teeth of wild stickleback, which had been feeding naturally, from Alaskan lakes.
Professor Paul Hart, also from the University of Leicester, explains: “The teeth might be tiny, but we discovered a very clear picture. Stickleback that feed from lake bottoms have very different tooth wear from those that eat water fleas and the like which swim around in open water”. The fossil teeth have almost exactly the same wear patterns as living stickleback but they have changed through time.
Dr. Mike Bell, from Stony Brook University adds, “Stickleback are spiky little characters, with armour and spines on their sides and along their backs. We found that evolutionary changes in these characteristic features were closely linked to shifts in feeding away from the lake bottom. As feeding changed over thousands of years, the stickleback in the fossil sequence evolved to have fewer spines.”
Scientifically, this is highly significant. That feeding and diet is an important control on evolution is exactly what would be expected from evolution by natural selection, but this is the first time that this aspect of Darwin’s theory has been directly testable using fossils that record real evolutionary change over many thousands of years. “We now know that by looking at microscopic chips and scratches on fish teeth we can investigate important evolutionary questions that were previously in the realm of the unknowable” concludes Purnell.
Marion O'Sullivan | alfa
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