Post #12 Seattle

Summer of 2015

My name is Adam King and I am a Science teacher at Eatonville Middle School. You may remember my story from last year when I helped map the magma chamber of Mt. St. Helens. This year I had the opportunity to work with a scientist at the Fred Hutchinson Cancer Research Institute in Seattle. This opportunity was provided by the SEP program at the Hutch which is overseen by Nancy Hutchinson. My scientist’s name is Sophie Archambeault and she works at the Peichel Lab. Now, the Hutch is mostly about cancer and diseases, and most of the scientists there are doing work in those fields, but some labs are set aside for basic Science. The Peichel Lab studies Sticklebacks, a fish.

Fishermen have probably used this fish, strung up on hooks, to go after cutthroat trout or maybe salmon. The fishermen probably don’t know that this fish, the Three Spine Stickleback, is becoming very important in the world of Science.

The Stickleback is a native fish and can be found in Puget Sound, the ocean, the rivers, and many lakes. When you walk in the shallows and see a fish dart away, chances are good that you just saw a Stickleback. Sticklebacks are found in North America, Europe, and Asia. It was thought for the longest time that there were dozens of closely related Stickleback species. That is, until scientists checked the DNA.

The DNA told a different story. All these fish were one species, and yet they lived in different locales and in salt, fresh, and brackish water. They even looked different. What was going on?

Have you noticed the short, rolling hills that look like large waves on the ocean just outside McKenna? Do you have a yard chock full of rounded rocks? Both effects were made by the mighty glaciers of the last Ice Age, and Yelm is about their most southern stop. When the glaciers retreated, lakes and streams formed in the gouged out pits made by the advancing ice. Marine (fish that live in salt water) Sticklebacks, which can tolerate fresh water, moved upstream into this virgin habitat. As the glacier retreat continued, the land uplifted, sort of like when you take your hand off a foam mattress. This uplift often cut off the new lakes and Sticklebacks were trapped. Sticklebacks evolved, changed their bodies, to adapt to their new situation. So how did they change?

Marine Sticklebacks are heavily covered in bony plates along their sides while small lake Sticklebacks have lost most of these bony plates. David Kingsley, an evolutionary biologist at Stanford University, looked for where this trait was controlled in the DNA. He found it - chromosome #4, in the Eda gene in 2005. Humans and Sticklebacks both have the Eda gene. If something goes wrong with the Eda gene in humans during embryonic development they develop ectodermal dysplasia. It is a rare disorder where you have no teeth, no hair, and can’t sweat. It was one of the first disorders described - it was even mentioned by Charles Darwin. While this is obviously bad in humans, non-expression of this gene in Sticklebacks has been selected for in small lakes. Why?

Lake Washington is a large lake separating Seattle and Bellevue. Evolution is happening with the Sticklebacks there within our lifetime. Sticklebacks are categorized as complete, partial, or low based upon the number of plates that are each fish has. For example, a complete Stickleback will generally have 32 or so plates. A low plated Stickleback will have around seven plates. You can think of these plates like armor found on knight. The plates protect the fish. Jun Kitano, a former researcher at the Peichel lab, collected data: a small survey of Sticklebacks in Lake Washington in 1957 found no complete fish, but that rose in in ‘68-69 to 6%, rose again by 1976 to 40.2%, and rose again to 49% in 2005! This is amazing! A period of intense natural selection was going on from the late ‘60s to the early ‘70s. Kitano proposes that the cause was a change in water clarity and cutthroat predation. Sewage used to be dumped directly into Lake Washington. This caused eutrophication, a fancy word which means that you didn’t want to swim in Lake Washington and you could only see one to two meters down. Sewage treatment plants were built in the sixties and the sewage dump stopped by 1968. By 1976, water clarity had improved to where you could see six to seven meters down. The improved water clarity means that cutthroat trout could more easily find their prey. So, completely plated Sticklebacks were more likely to survive (they weren’t eaten) and their percentage of the population soared. Evolution on a short time scale. Sophie, the scientist I worked with, had another question to ask.

There are a cluster of traits that go with the Eda gene. Not only does the number of plates change, but so does the size of the fish, how they school, and neuromast configuration (neuromasts are like motion sensors on the sides of fish). So are all of these traits linked, or is there just one spot on the DNA (the fancy word is pleiotropy) that is controlling these traits? Sophie and Hilary had collected 188 Lake Washington Sticklebacks. Fins were snipped so DNA could be collected. This is where I entered the picture. My task was to determine the phenotype, or physical type, of all these fish. This job was not high-tech. I used a jeweler’s loupe, which is a magnify glass, to count the plates on each fish. This count told you if the fish was complete, partial, or low plated. Sophie then walked me through my next task which was to do a PCR, a way to examine a specific piece of DNA of each fish. This part was high-tech and a little nerve wracking because I didn’t want to ruin all of Sophie’s hard work. Happily, everything worked well. I then entered the phenotype (plates) and genotype (DNA) information into a spreadsheet so we could see the results.

One finding from examining the spreadsheet numbers was that the percentage of complete plated Sticklebacks is now up to 56% in Lake Washington. A second finding was that the traits (plates, schooling, neuromast) most closely associate with a piece of DNA called Stn382. Let me use this analogy. Finding the single gene, or genes, that control these these traits is like finding a needle in a field of haystacks. So these findings narrow the search down to two haystacks instead of field of haystacks. The progress is slow, but happen.

So what happens next? In Science, it seems that whenever a question is answered, it leads to several more questions. Sophie already has tanks with baby Sticklebacks hybrids to carry on with her current quest. I plan to, along with my 7th grade students, to ask the question, “Why do Sticklebacks lose their plates in small freshwater lakes?” Jun Kitano has provided compelling data for the proposal that cutthroat predation causes selection for plated Sticklebacks, but what about the opposite? I have set up two tanks in my classroom which will be stocked with Sticklebacks and have several experiments planned. It should be fun, and will no doubt lead to further questions.