Human Actions Have Quick Impacts On Fish Species’ Evolution

By on February 24, 2016

Hagerty, Ryan, USFWS

A new study out of the University of British Columbia has found that human actions can have broad and quick effects on the evolution of fish species. The research followed along after crayfish were introduced into one of the province’s lakes to see what effects there were on fish living there.

The results of the work, carried out in Enos Lake, show that human actions can speed up the typically slow process of evolution for fish. That can actually results in negative impacts for the fish instead of positive evolutionary changes.

All it took was three years, scientists say, for two species of threespine sticklebacks living in Enos Lake to disappear after the crayfish incursion. The fish had previously existed in the lake for thousands of years.

During that time, the two species of sticklebacks had each carried out different but similar roles. One lived more toward the lake’s center and fed on zooplankton while the other lived more near to shore and depended on insects that spent their larval stages in the water.

But following the introduction of crayfish into Enos Lake by humans, the balance that the two species of sticklebacks enjoyed went away. The crayfish liked to feed on stickleback eggs, prompting populations of the fish that breed near crayfish-filled areas to move their breeding sites.

The result of this move was increased breeding between the two species of sticklebacks. And, eventually, scientists saw that both species of the fish had been lost, only to merge together to become one new species of threespine stickleback.

This new species doesn’t carry out all the ecological roles as the other two did. Instead of covering both the deeps and the shallows of Enos Lake, the new species only lives in more medium-depth areas and feed on larger insects.

This shift has caused changes to the lake’s food chain, notably that there are more insects emerging from the nearshore areas than there has even been before. With the new hybrid, researchers have also found that leaves that fall into the lake do not decompose as quickly as they once did.

The shift that researchers observed between the stickleback species is known as reverse speciation. When it occurs, scientists say, there are always impacts to the surrounding ecosystem because there are fewer ecological roles being filled than there were to begin with.

Reverse speciation, in many cases caused by human actions, is becoming an increasingly common problem, researchers say. And parts of Canada may be at greater risk than other regions around the world to feel its impacts because of the many younger species, in terms of evolutionary history, that can be found in the country.

Much of Canada’s biodiversity, particularly fish in lakes and rivers, are considered to be “young” species that formed in the last 12,000 years or so, scientists say. This type of evolution can occur with remarkable quickness and cause alterations to the ecology of surrounding ecosystems. And they hope that their findings will be useful in conservation efforts in the future.

Full results of the study are published online in the journal Current Biology.


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