10 million year-old chips reveal link between fish diet and evolution
27 September 2007
Chips from 10 million years ago have revealed new insights into fish diets and their influence on fish evolution, according to new research featured in this week's issue of the journal Science.
The chips were found, along with scratches, on the teeth of fossil stickleback fish and reveal for the first time how changes in the way an animal feeds control its evolution over thousands of years.
A stickleback's mouth
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.
Tips of two teeth showing chips and scratches
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.
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1. The paper, "Correlated Evolution and Dietary Change in Fossil Stickleback" by Mark Purnell, Michael Bell, David Baines, Paul Hart and Matthew Travis is published in the September 28 issue of Science. Copies of the full paper can be obtained from Science.
Mark Purnell is a NERC Advanced Research Fellow and Lecturer in the Department of Geology, University of Leicester, UK. David Baines is Research Assistant in the same department, and Paul Hart is Professor in the Department of Biology
Michael Bell is Professor, Department of Ecology & Evolution, Stony Brook University, USA. Matthew Travis is now at the Department of Biological Sciences, Rowan University, USA.
2. The research on tooth wear was funded by the Natural Environment Research Council (NERC), one of the UK's seven Research Councils. NERC receives about £370m a year from the Government's science budget to fund and carry out impartial scientific research in the sciences of the environment. NERC trains the next generation of independent environmental scientists. It is addressing some of the key questions facing mankind such as global warming, renewable energy and sustainable economic development.
3. Research at Stony Brook University was supported by grants from the Geology and Paleontology and the Population Biology programs at the National Science Foundation of the USA, which supports pure and applied science.
Press release: 37/07
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