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"Rapid evolution not only occurs, but runs across the food web in ways we are only now starting to understand," says David Post. (Credit: David Allen/Flickr)

evolution

Dams sparked quick evolution in competing fish

When Colonial era settlers dammed Connecticut waterways, they triggered sudden and parallel evolutionary changes in the alewife and bluegill fish competing for food.

Earlier studies documented the decrease in size and changes in gill structure of members of the alewife species cut off from access to the sea in newly dammed lakes.

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From Bride Lake in Connecticut, an alewife with access to the sea grows larger than adult alewife from landlocked Rogers Lake, which was dammed by Colonial settlers. Evolution has not only reshaped the alewife, but also bluegills, who compete with the fish for food. (Credit: Post lab/Yale)
From Bride Lake in Connecticut, an alewife with access to the sea grows larger than adult alewife from landlocked Rogers Lake, which was dammed by Colonial settlers. Evolution has not only reshaped the alewife, but also bluegills, who compete with the fish for food. (Credit: Post lab/Yale)

The new study, published online in the Proceedings of the Royal Society B, found similar changes in feeding habits of the bluegill, which also showed greater ability to feed on smaller zooplankton found in landlocked lakes the species shared with the alewife.

“Rapid evolution not only occurs, but runs across the food web in ways we are only now starting to understand,” says David Post, professor of ecology and evolutionary biology at Yale University and senior author the paper.

Alewife changes

In its natural state, the small herring-like alewife swarms into Connecticut lakes, devours insects and all large zooplankton growing unmolested for most of the year, and then heads back out to sea, where itself becomes the main course of many of the ocean’s fishes.

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However, the alewife underwent fundamental changes when lakes were dammed in Connecticut 300 years ago. The landlocked alewife became smaller, eliminated all large zooplankton in the lakes, and underwent changes in its gill structure that enabled it to eat the smaller zooplankton that grew there.

Magnus Huss, a postdoctoral fellow in Post’s lab, now at the Swedish University of Agricultural Sciences, wanted to see if the strong effects of landlocked alewives on the zooplankton community would lead to similar changes in bluegills.

Post, Huss, and coauthors found that bluegills in lakes with ocean access did not feed well on small zooplankton, but bluegills living in lakes isolated from the ocean with the landlocked alewives did just fine on a diet of smaller fare.

Post says these studies show that conservation efforts must take into account the entire food network when dealing with environmental changes such as dam construction or the introduction of new species into environments.

“Any time we have invasive species evolving rapidly, we can expect to see changes in competitors as well,” Post says.

Source: Yale University

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