Evolutionary biologists have long assumed that when an individual of a species wanders into a different environment than it is adapted to, it will be at a competitive disadvantage compared to natives of the same species which are adapted to that environment. Studying fish in Canada, scientists found the opposite.
Evolutionary theory suggests that taking the fish that are adapted to the lake environment and placing them into the stream would put them at a competitive disadvantage compared with the residents. In the dog-eat-dog world of natural selection, outsiders are often poorly adapted to a new environment and less likely to survive or pass on their genes. In the case of the sticklebacks, that’s because the lake-adapted fish have different physical traits from their stream-adapted cousins — such as their overall size, immune traits, body shape and defenses against predators — that allow them to fare better back home but not necessarily in other environments.
Yet when the researchers did a series of experiments placing varying numbers of fish from one habitat into the other habitat with local fish, they found the transplants fared surprisingly well. Monitoring the fish in underwater cages over time, the researchers observed that survival had less to do with where a fish was from, and more to do with whether they were the common or rare type within their cage. In either habitat, when stream fish were in the minority, they survived better than when they were in the majority, for instance.
The scientists found that immigrants could fly under the radar in the face of some threats, which helped them beat the odds.
“You come in and you eat something nobody else around you eats, so you aren’t competing for food,” Bolnick says. “The local parasites don’t know what to do with you because you have an unfamiliar immune system. So you’re better off than the residents.” Paper. (paywall) – Daniel I. Bolnick, William E. Stutz. Frequency dependence limits divergent evolution by favouring rare immigrants over residents. Nature, 2017; DOI: 10.1038/nature22351 More.
Much more of interest in the release. The authors are surprisingly bold about challenging textbook zombie theory. Hope that works out okay for them.
The Darwinian understanding of evolution requires the theorist to develop a science-level prediction about what will survive that goes beyond mere tautology. That quest has consistently failed.
One approach would be to treat evolution merely as a history, which it in fact is. Patterns can certainly be studied and they are doubtless illuminating. But grand theories would be treated with the skepticism they have justly earned.
See also: What the fossils told us in their own words
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