This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A research team from the University of Bern has shown in a large-scale field experiment that populations of the same fish species can be much more fine-tuned to their local environments than previously thought. Habitats that appear nearly identical to us can therefore make a decisive difference in evolution.
This hidden diversity is not only key to understanding how biodiversity arises, but also has important implications for its conservation. Since Charles Darwin, natural selection has been recognized as the major driving force of evolution. Genetically heritable traits that give individuals an advantage in their local environment increase in frequency over generations.
As a result, populations become evolutionarily adapted to their environments and can gradually diverge from one another—ultimately giving rise to distinct new species. Recurring patterns in nature, such as similar body shapes in similar habitats, are therefore often taken as evidence for natural selection: Individuals with certain traits had an advantage in their particular environment and were consequently more likely to survive and reproduce. However, demonstrating that a population is truly adapted to its local environment requires a more direct test: Individuals must perform better in their own habitat than individuals originating from elsewhere.
This is where a new study led by Dr. Marius Roesti of the Institute of Ecology and Evolution at the University of Bern comes in. Through a carefully designed field experiment, the researchers were able not only to test evolutionary adaptation directly, but also to determine how specifically populations are adapted to local conditions.
Their model organism was the threespine stickleback (Gasterosteus aculeatus), a small fish found in a wide range of habitats across the Northern Hemisphere—from large lakes to small streams—where populations repeatedly evolve similar characteristics under similar conditions. As the new experimental results reveal, however, differences among stickleback populations do not simply reflect adaptation to broad habitat types such as "lake" and "stream." Instead, much of their adaptation goes beyond these broad habitat differences and is finely tuned to the unique conditions of individual locations. The findings shed new light on the fine scale at which biodiversity arises and have important implications for its conservation.
The research is published in the Proceedings of the National Academy of Sciences. For their field experiment, the research team bred sticklebacks originating from Lake Constance—one of the largest lakes in mainland Europe—and from four tributary streams in Switzerland, Liechtenstein and Germany. The fish were raised for two generations under identical laboratory conditions at the University of Bern.
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