After a short three-month hiatus, the Loyalsock trout crew is loading the trucks and preparing to hit the streams for “spring” sampling. The term spring is really being thrown around loosely here…there is snow on the ground, it was 13°F this morning, and trees and flowers still appear dead (some may call this death-stage dormancy, and while science would call them right, I say you can’t trust a plant until it comes back green).
The goal of this sampling is easy- go out, find fish, collect gill samples, and ship gills to West Virginia so they can analyze for gene expression. If all goes as planned, at the end of next week we will have collected gill samples every 1-3 months for a full year. It will also up our total sample size to near 600.
That’s a lot of vials of fish gills. More vials of fish gills than most other studies. And, our gills are collected on wild trout in natural systems. My background on gene expression studies is severely lacking, but I’ve learned that we are sailing in largely uncharted waters with this study. Specifically, our sample sizes are large, we are not working in a controlled laboratory environment, and we have multiple samples on the same individual fish over time.
That’s not to discount the significance of any other study- all of this stuff is pretty cutting edge, and valuable data is being gathered from everyone working in this field. In fact, lab studies have a lot of advantages that wild streams don’t. I have to wait for stream temperature to rise and, because Loyalsock is two hours away, hope I pick a critical time for collecting tissue samples. But, with the flip of a switch, we can change temperature in artificial stream labs and immediately expose fish to temperatures that we are interested in measuring heat shock expression in (recall: heat shock proteins are produced in response to heat stress to prevent cell death).
But, streams don’t really work like labs. Stream temperatures rise and fall much faster than we can readily mimic in a laboratory environment. And, gene expression is highly sensitive to this variation. This leaves us at a bit of a catch-22. We can control temperature in labs but, because tight control leaves little variation, the data may not reflect patterns of gene expression in wild trout populations. Streams, on the other hand, have all the variability we need, but we don’t know what aspect of the variation actually matters to trout. Simply put, we don’t actually know what triggers heat shock protein expression. Yes, it’s heat. But is it average stream temperature over the last three days? Week? Month? Or is it difference in maximum and minimum stream temperature? Or, time at a certain temperature? Even if we did know what aspect of variation triggered protein expression, it would be really hard to find the sampling window of most interest without camping streamside and recording temperature every 30 minutes.
We’ve hit this wall with our data so far. Some of our lowest heat shock protein expression is from July, when water temperature were near their highest. No, this doesn’t mean our data are wrong. It likely means that conditions between May-July triggered heat shock protein expression, and once the proteins were floating around in the fish’s’ system, they stopped expressing the gene. So, we missed the critical window.
And, that’s okay. It’s still providing us great information into how trout are responding, molecularly, to stream temperatures. It also gives us a better idea of when we should sample if we want to catch peak gene expression. Like, maybe March. No, stream temperature are not high in March, but they will be starting to rise from winter lows. And, we know expression in May is not high. So, could it be this increase in temperature in March that triggers expression? Maybe. And we’ll soon know