Who doesn’t love wearing a little bling every once in a while? Mouse lemurs. That’s who. This week, Bobby, trusty Duke Lemur Center veterinarian, along with the help of Erin, research manager extraordinaire, outfitted ten tiny mouse lemurs with ten tiny temperature-sensitive collars. And I mean tiny. These collars, weighing about as much as a paperclip and boasting a circumference maybe a tad bit bigger than the width of your thumb, are the pride and joy of a side project that I’m conducting at the Duke Lemur Center.
This side project, which I like to think of as the “less-than-sub-par-dissertation-research-should-my-work-on-hibernation-genomics-fail-in-epic-fashion” is a fun little project I conjured up last year, mainly so I can work with adorable captive mouse lemurs. Also, so I stop panicking about how risky my actual dissertation work is.
I call it the diet supplementation study. Here’s why: If you’ve been following along, you know that I study hibernation physiology in dwarf lemurs. And you might also know that they can hibernate for up to 7 months out of the year. Mouse lemurs, in the same family as dwarf lemurs, also quasi-hibernate. It’s a phenomenon called daily torpor. Outwardly, it looks the same as hibernation, although it is expressed on a much smaller scale. Metabolic rate and body temperature are depressed, as in hibernation, but usually for less than 24 hours at a time. So, species like ground squirrels, black bears, and my dwarf lemurs, would be called classical “hibernators. Makes sense, right? Mouse lemurs, on the other hand, are colloquially known by those of us in the hibernation field, as “torpidators” (Hey, we watch dormant animals for a living! You need to stimulate brain matter somehow. Give us, poor researchers, a break!).
Daily torpor, at least in mouse lemurs, is a really flexible response. There have been numerous studies on mouse lemur torpor patterns in the western region of Madagascar, offering loads of insight about metabolic rate during torpor, how low body temperature can go, and the fact that females vs. males are more likely to use torpor (e.g. some males don’t at all, staying active the entire winter). And here’s where the “flexibility” part comes in. We also know that torpor episodes vary in intensity, duration, and frequency between populations of the little guys, within populations (with some individuals in the group showing different usage of torpor), and even within individuals (i.e. they can change their torpor usage from year to year, and even month to month. So, for example, maybe one animal used torpor throughout the whole winter in 2012, but only went into torpor during two days in 2013). Weird! So this got me thinking: What factors are influencing these mysterious patterns? I’ve already ruined the punch-line. Diet. Of course, this is all conjecture on my part, but what if foods the animals were eating prior to torpor season are shaping torpor usage during the winter? It’s pretty well-established, and seems intuitive (at least to me), that the amount of fat that is stored will affect how long an animal can hibernate (or torpidate, if you will…and I, of course, will). If an animal runs out of fat stores in the middle of winter, they’re pretty much up the creek without a paddle. Hibernators/torpidators are not known for being particularly good paddlers. So we know that getting really, really chubby matters, but imagine for a moment that not only the quantity of fat stored is important, but also (wait for it…) the quality!
Using captive mouse lemur at Duke Lemur Center, I can actually test this crazy, speculative theory! This is science at it’s finest, folks! Beautifully designed studies in the lab that can begin to answer the questions I am after, by controlling everything but the variables I want to test. The guts of my experiment rely upon two different diets, which I’ve modified with some help from those who’ve done similar studies in the past (I’m standing…well, wobbling really, on the shoulders of giants. They’re very tall!). These two diets are identical, with the notable exception of the type of fat that they contain.
The ten mouse lemurs in my study are split into two groups. Each group will be fed one of the two diets for two months before they start to ‘torpidate’, at which point they get fitted with their fancy new necklaces. These necklaces allow me to collect body temperature data at hourly intervals throughout the torpor period. I can then determine if one type of diet was correlated with lower body temperatures or longer torpor episodes. In other words: Does diet, indeed, matter?
Sounds really simple, right? It turns out, it’s not. Stay tuned for the messy details!
It’s a jungle out there!