Use Clues From Rapid Evolution To Design Better Fish Gills

Why do you think giraffes have such long necks? It’s a question that has perplexed scientists for years. Do you think giraffes have long necks to reach food in high places? Maybe you are onto something! Or do you think that maybe their necks are the ultimate weapon for fighting? That is another theory.

What scientists now know is that the fossil record shows giraffes’ necks used to be much shorter, but over millions of years, things changed. Today, their necks are the record holders for the longest necks in the animal kingdom! So what’s going on here?

Tracing The Evolution Of Organisms

If you said evolution you were right! Evolution is the theory that all of the living things on Earth developed from earlier types of living things. Since humans were not around 3.5 billion years ago—when it is thought the first very simple life forms emerged on Earth—there are a lot of unknowns about what really happened. So scientists use fossil records to support their theories, like the giraffe and its amazing neck.

When people think about the evolution of organisms, they usually think about change that happens over extended periods of time. For example, it took about 20,000 years for a chihuahua to evolve from a wolf. But can organisms evolve more quickly? And what influence can people have on the evolution of organisms?

How Fish Moved To The Mountains

Recently, researchers at the University of Wyoming studied the rapid evolution of fish in alpine lakes. Scientists compared the physical differences between trout that had been stocked, or physically put into the lake by humans, and trout at a hatchery, where fish are raised in captivity from eggs to be released into lakes and streams.

Just to be clear here, the fish in these alpine lakes are not native, or naturally found there. Formed by glaciers in the mountains of western North America, alpine lakes had no fish until the 1900s. Humans, like pioneer Finis Mitchell, brought cutthroat, brook, and golden trout up to the lakes and released them so people could catch them for food and, eventually, sport.

In their usual habitats, these fish enjoy aquatic (water) insects, like stoneflies and mayflies, and terrestrial (land) insects, too, like ants, beetles, crickets, and grasshoppers, that come close to the water surface. But high in the cold mountains where the fish were moved, those insects weren’t as plentiful. Plus, the lakes are frozen for up to half the year, so there wasn’t much plant life either. What do you think there was for the trout to eat?

The Search For Food Forces Evolution

Imagine going to a new town, and they don’t have the restaurants you like. What would you do? The trout in the alpine lakes had a similar problem, but they couldn’t just order a takeout. These trout normally eat insects, but in their new home, there wasn’t much of their favorite food.

The trout adapted to consume zooplankton, or microscopic organisms found in the alpine lakes. All trout have gill rakers, bone, or cartilage in the esophagus that help fish eat. Fish use gill rakers to filter prey, such as plankton, from the water. Basically, they work like a sieve to catch tiny food. The more gill rakers they have, the easier and more efficient it is for them to eat. Different species of fish have different lengths, densities, and numbers of gill rakers.

When researchers compared the descendants of trout stocked in the lakes during the 1900s to fish that were presently living in hatcheries, they discovered that descendants of the earlier fish had more gill rakers. The alpine lake trout had adapted to better use the plankton as a food source. Usually, scientists expect evolution to occur over thousands or millions of years. But these fish had rapidly evolved in just over a century!

“I think something that’s interesting to just think about the big picture here is humans are impacting biodiversity at sort of an unprecedented rate.” – Will Walkey, a reporter at Wyoming Public Media in Laramie, Wyoming

The trout adapted to life in these alpine lakes because each generation developed more gill rakers, making it easier to feed on plankton.

• What other ways do you think the trout could have adapted?
• How do you think their presence in the lakes affected the original ecosystem?

Evolution is a natural process that happens to living organisms. However, scientists and engineers often use the shapes and forms that evolve in nature as models. Using those models, they can design new materials or structures to solve human problems. This approach is called biomimicry. Today, you will be an engineer using biomimicry to redesign gill rakers.

Your challenge is to design improved gill rakers that will strain pepper flakes out of water. The pepper flakes represent the zooplankton. Your engineered gill rakers must be made from only materials you can find in your home. Use your imagination to create a new way for the trout (gill rakers) to strain the zooplankton (the pepper) from the water to get as much pepper in their bellies as possible.

Below is a materials list with some ideas of things you can use, but get creative and see what you have available.

Materials:

• Pepper
• A bowl of water
• Materials from around your home such as:
  – Paper towel and/or toilet paper rolls
  – Paper plates
  – Paper/plastic cups
  – Scrap paper
  – Cardboard
  – Construction paper
  – Cotton balls
  – Scissors
  – Tape
  –  Glue
  – Markers/crayons/colored pencils
  – Pipe cleaners
  – Craft sticks
  – Rubber bands

Test out your engineering magic! Ask an adult to help you get some water in a big bowl. Sprinkle pepper on the top of the water. Use your new and improved gill rakers to collect as many flakes as possible. As you do, ask yourself:

• How much of the pepper did you get out of the bowl?
• Which arrangement of gill rakers trapped the most pepper? Why do you think this is?
• Which materials worked best as gill rakers? What qualities do those materials have that make them good gill rakers?

Engineers test their designs several times during the engineering process. If you have time, rethink some improvements for your gill rakers’ design and see if you can collect more pepper in a shorter amount of time.

How might this design be useful for solving other challenges? Can you imagine a way your biomimicry-inspired design could solve a problem for humans? Researchers are already using what they’ve learned about gill rakers to reduce clogging in filters and remove microplastics and oil from wastewater. What would you invent?

Interested in evolution? There is much more you can learn!

• Read about other organisms that have experienced rapid evolution such as green anole lizards, tawny owls, Polynesian field crickets, and bedbugs. They have all adapted at a rapid pace to changes in the environment.
• Read a book excerpt from the book, Explaining Life Through Evolution, by Prosanta Chakrabarty.
• Read any of these books on evolution that are written for students like you!
• Learn more about biomimicry with engineers studying gecko feet and cockroaches. Then try additional projects using biomimicry in engineering design.
• These trout are not the only animals that feed by filtering plankton through gill rakers. Discover how manta rays do it.

Next-Generation Science Standards

This resource works toward the following performance expectations:

• MS-LS4-1 Biological Evolution: Unity and Diversity – Analyze and interpret data for patterns in the fossil record that document the existence, diversity, extinction, and change of life forms throughout the history of life on Earth under the assumption that natural laws operate today as in the past.

Credits
Lesson by Svea Andersen
Copyediting by Erica Williams
Digital Production by Sandy Roberts