Science Exchange Stories: Marcus Welker PhD at Dartmouth

Marcus Welker collecting samples.
Marcus Welker collecting samples.

Marcus Welker is a 4th year PhD student at Dartmouth College studying salmon migration in the Northeast United States and southern Quebec, Canada. His hypotheses and methods are both surprising and fascinating – check out our interview below!

Q: What do you research?

A:  I study salmon – in particular, I’m interested in how they migrate.  Salmon are born in rivers, go out to the ocean or large lakes, and find their way back to the rivers where they were born. This has been known for 100’s of years, but in the last 50-60 years, people have tried to understand how they do it – what sensory mechanisms do they use and what is it about the environment that signals them home? – to improve hatchery practices habitat restoration and fisheries.

We believe that by smelling amino acids when they are in the river as juveniles they make this really powerful memory of the smell of the river (imprinting). Then they go to the ocean or lake and do their adult thing, get huge, and come back to their river of origin (homing), because they remember the smell of the amino acids and can discriminate their birth river from other rivers.

Q: How are you testing this hypothesis?

A: One set of studies I’m doing is going out to the salmons’ environment and measuring these amino acids. For the other study, I’m simulating the imprinting and homing process in a hatchery by dosing the water with amino acids while the fish are juveniles, rearing them to adulthood in the hatchery, and then testing their behavioral preferences as adults. For both studies, it is crucial to know the amino acid signature of the water.

In the case of our simulated imprinting and homing experiment, we expect that juveniles exposed to amino acids will exhibit a preference for the amino acids that they were exposed to as adults, whereas unexposed fish will not exhibit a preference.

Q: How will you test the behavior of the fish as adults?

A: In collaboration with the United States Fish and Wildlife Service, we built a big two-choice fish maze. By manipulating the water chemistry in the different branches of the maze, we can test the preference of the fish for different amino acids. The behavior of the fish in the maze is monitored using an underwater video camera and a telemetry system.

To test out the maze before the imprinted fish reached maturity, we ran an experiment with adult salmon returning to the outlet ditch of a hatchery on shores of Lake Champlain. The goal was to filter the amino acids in one branch of the maze, while leaving the other unfiltered. Water samples from both branches of the maze were analyzed at the University of Nebraska Medical Center’s Protein Structure Core Facility through Science Exchange. Samples from the simulated imprinting and homing experiment were also analyzed.

Q: What went into your decision to use Science Exchange?

A: I needed to produce some data that I was unable to do given the constraints of my laboratory and of those around me. This provided a tool to produce data rapidly and at a crucial period of my PhD.

Q: What was it like convincing your advisors that you needed to contract out some of your work?

A: I have a great committee, however they were concerned about me contracting all of my work. They saw a great benefit to contracting a small subsample of my work, but were concerned that it was important to me as a PhD student to go through these challenging processes myself.

Therefore, at that critical period of my PhD, I needed analysis done efficiently, in order to better frame my future research and defend my research to my committee; contracting the work out was the best option. I believe the combo of both personal lab work and contracted research creates a powerful tool for graduate students.

Q: Do you have any advice for other graduate students that are in a similar situation?

A: I think the trick is to find the balance. In my case, I’m a young PhD student, and I’m deploying methods for the first time. It’s very particular for every person and experience.

I think that in many cases PhD students are being asked to do some type of road map and planning. That’s often a time when you need some data, and it’s a unique time to use a service like Science Exchange to get the data you need to satisfy your committee. Later on you can figure out how to produce your own data. Either contracting out or using your own lab, it’s something that you can decide.


Tess Mayall


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