Photo by Bryan Roeder of a hibernating ground squirrel courtesy of Dr. Sandra Martin.
I sent these great comments and questions about a recent blog on Dr. Sandra Martin's work with hibernating ground squirrels to the expert for her response:
Halie J: I really found this article interesting. Knowing that animals gain muscle mass while they hibernate is fascinating and I'd like to know more about how that happens. I'm not sure it's a good thing they are losing body mass though because isn't it healthier to have more body mass then muscle mass? If fasting increases the antioxidant levels in the body how come it's not healthy to fast for weight loss and is that why you have to fast for a prolonged period of time before a blood test? If you could please get back to me I'd appreciate it.
Kayla G: I think that your post really came to my attention since I'm not familiar with animal hibernation or fasting. It was really interesting to read! Animals amaze me how they can actually go that long with no food or exorcise. What makes the ground squirrels muscle volume increase while it is sleeping? I was wondering since the elephant seals reason has to do with antioxidants.
Here are the responses from Dr. Martin:
We think hibernating ground squirrels are really interesting too! They do lots of things that are unusual or even unhealthy for humans. For example, these animals eat to get fat in late summer and fall, but then suddenly stop eating and begin hibernating. They literally fast all winter, living off of that stored fat. This is a great survival strategy for these animals because their food is not readily available during winter. So, Haley, in the case of hibernating ground squirrels, body mass loss is normal and healthy, and most of the loss is from fat that was deliberately stored for this purpose. We've done blood tests on some squirrels during this long period without food and know that they are in a stable state for long term fasting. Remember that these squirrels fast for ~6 months, so that's not really comparable to our overnight fast for a blood test.
Kayla: Pteryxx is absolutely right, we've discovered something really interesting about these squirrels; they gain muscle mass while they are still hibernating and fasting. Now we are trying to figure out exactly how they do this.
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The original summary post claimed that they gained "muscle volume." Are these data based on measurements of (fresh) muscle volues, fresh weights, or dry weights?
If dry mass increases (i.e. it's not simnply a hydration effect), then where are the new amino acids coming from?
Hi Sven - thanks for the inquiry. We have a few types of data supporting this claim. The original finding was indeed a gain in muscle volume, measured by a series of MRI scans taken of a few animals over an entire year. We've now been able to confirm this with wet weights for 5 different muscles, collected from a number of animals across the winter hibernation season. In other experiments, we could not detect a change in protein concentration of homogenized muscle samples through winter and into spring, so we think this is more than simply that muscles are losing water in winter and gaining it back in spring.
So, you are correct, our next step is to sort out the 'hows' of what appears to be new muscle protein synthesis in these animals towards the end of the hibernation season. We have several experiments underway, please stay tuned for those results!
Allyson - the person doing the experiments