Could a butterfly flapping its wings in Brazil cause a hurricane in Texas? American meteorologist Edward Lorenz once asked this question to show that small intrusions into complex systems can have unexpected effects.
This phenomenon, known as the butterfly effect, also applies to the networks of nature, whose interrelationships are rarely known. However, in many places people step in without wasting any thought of what they might release.
Finnish biologists describe an interesting example of this in the current issue of the scientific journal to know. In their study, they show how the overfishing of capelin, a small school fish in the Barents Sea, is making salmon that other fishermen pull from waters several kilometers away in Finland’s Tino River smaller.
For their study, the team led by biologist Yann Czorlich of Finland’s University of Turku evaluated data from 40 years of hunting and combined it with results from genetic analyzes of salmon. Biologists have found that there is a relationship between the size of the Capelin clan in the Barents Sea and the frequency of a particular genetic variant in the tino salmon genome, which makes the fish sexually mature earlier and become smaller. Whenever capelin populations collapsed due to overfishing – which occurred several times during the study period – this genetic variant accumulated in salmon.
In order to survive, animals and plants must adapt more quickly in the Anthropocene.
According to the authors, this connection, surprising at first glance, has to do with the complex life cycle of salmon. Fish are born in the fresh waters of rivers and then migrate to the sea. They spend their childhood and adolescence there, so to speak. Once they are sexually mature, they migrate back to the river where they were born to lay eggs.
In the Barents Sea, capelin schools – huge in good times – are one of the main food sources for the young salmon that live there. If fishing fleets pull a lot of capelin from the sea, then predatory fish find little to eat. The deficiency appears to result in a change in their genome that causes the salmon to mature earlier and remain smaller. The study authors wrote in to know. Biologists also talk about “evolution in rapid motion”.
Charles Darwin, who established the theory of evolution more than 160 years ago in his book On the Origin of Species, still posits that evolution is a slow process. It must take thousands or even millions of years for new species to form through mutation and selection (macroevolution) or for existing species to change (microevolution).
In the Anthropocene – that is, in the era formed by humans – the species Homo sapiens changed their environment and thus the conditions of other animals and plants at a much faster rate than in the history of the Earth. In this large-scale involuntary experiment, animals and plants must change quickly in order to have a chance of survival.
It has long been known that humans, as a selection factor, can directly influence and accelerate the development of animals and plants. An example is the elephants in Mozambique that have lost their tusks because they make them unattractive to poachers and allow them to survive. For a similar reason, many large-horned sheep in the United States no longer have thick horns, but rather slim horns. Cod has become noticeably thinner and shorter in recent decades due to the infiltration of small specimens through the nets of fishing fleets.
The current study is one of the few understandable examples of how humans influence evolution not only directly, but also indirectly: salmon are shrinking because humans catch an entirely different fish in an entirely different place. Ironically, capelin in the Barents Sea is also widely fished to feed salmon in aquaculture.
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