L'hiver (Winter)
Winter is approaching here in the Ariège. If you look outside in the afternoons, however, you’d likely not notice if it wasn’t for the bare deciduous trees. The past couple weeks have been remarkably clear and sunny, making it pleasant enough to eat lunch out on a patio or take a jog in just shorts and a t-shirt (both of which I have been fortunate enough to do this past week). Having moved here from the Midwestern U.S., this doesn’t seem so bad for late November! What’s been most intriguing to me is the daily flux in temperature – each morning frost covers the slate roofs and the car windshield while I bundle up in my winter parka and knit cap, but by mid-day I can sit outside and read (which I’ve also been fortunate enough to do this week). While I am more than happy to enjoy this lovely weather as an endotherm, my thoughts of course turn to the question of, “How does this weather affect the lizards?”
Last week, Mahaut and I went to one of our study sites, the stone bridge over the Lez River in Aubert. I was hoping that, if the conditions were right, we might spot a lizard or two out basking. Much to my surprise, we found dozens just in one small section of the wall!
Now I know this won’t be a particularly surprising find to others who have spent more time here than I have, but I was quite shocked to see so many lizards out active and basking when just a few hours earlier frost covered the ground. Growing up in the snow-covered terrain of Western New York, I have generally perceived of the change of seasons and hibernation as a kind of on-off switch: the critters I loved were active in the summer and inactive in the winter, with very little in-between time. My field work in Colorado and Iowa these past years challenged this notion a bit, with observations that garter snakes would emerge from their hibernacula as early as mid-March on warm days, but then go back down when things cooled. This up-and-down could last for several months until temperatures became suitably and consistently warm enough for dispersal in late April or May. Despite this, I still generally thought of overwintering as a binary operation.
At the Society of Integrative and Comparative Biology meeting last January in New Orleans, however, I saw a great talk by Peter Zani from the University of Wisconsin-Stevens Point titled, “Daily emergence in crevice-dwelling lizards during winter is related to temperature, not light.” The study found that side-blotched lizards (Uta stansburiana) rely on temperature, rather than light, to determine if they should come out and bask while overwintering in rocky crevices. He described field observations and some very cool lab experiments that he’d employed to study overwintering physiology and behavior. These lizards from populations in eastern Oregon are active more or less all winter – if I recall, he claimed that he’d seen them out basking every month of the year except January (though the reason was most likely that he wasn’t there at the right time, not that they weren’t basking). This was a real epiphany for me, on par with the first time I was told that birds are actually dinosaurs. OK, maybe it wasn’t quite that mind-blowing, but nonetheless was an important shift for someone who thought previously of overwintering in reptiles and amphibians as a discrete state change where animals essential remained “off” until spring.
The past couple years, I’ve given a fair bit of thought to behaviour and energetics of overwintering in reptiles and amphibians (which I’ll write more about in a future post). And I’m excited to know that I’ll be working with some lizards for whom winter conditions, and their capacity to respond, are undoubtedly quite important to their survival and reproduction. And yet we know very little about this! With these questions in mind, we’ve kept the animals from our recent experiment and are currently hibernating them at 8 ºC in the labs at the CNRS in Moulis and Pic du Midi. I hope to begin next week measuring heart rates and metabolic rates to test for the effects of low-oxygen environments on lizard physiology during this state of low energy-demand. Look for some updates (hopefully interesting ones!) soon.
Last week, Mahaut and I went to one of our study sites, the stone bridge over the Lez River in Aubert. I was hoping that, if the conditions were right, we might spot a lizard or two out basking. Much to my surprise, we found dozens just in one small section of the wall!
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| At the bottom right is the spot on the wall, adjacent to the bridge, where we saw many lizards basking last week. |
Now I know this won’t be a particularly surprising find to others who have spent more time here than I have, but I was quite shocked to see so many lizards out active and basking when just a few hours earlier frost covered the ground. Growing up in the snow-covered terrain of Western New York, I have generally perceived of the change of seasons and hibernation as a kind of on-off switch: the critters I loved were active in the summer and inactive in the winter, with very little in-between time. My field work in Colorado and Iowa these past years challenged this notion a bit, with observations that garter snakes would emerge from their hibernacula as early as mid-March on warm days, but then go back down when things cooled. This up-and-down could last for several months until temperatures became suitably and consistently warm enough for dispersal in late April or May. Despite this, I still generally thought of overwintering as a binary operation.
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| A Western Terrestrial Garter Snake (Thamnophis elegans) slithering over a snowpatch in March. The snake was basking just outside its hibernation burrow in a city park in Denver, CO, USA. |
At the Society of Integrative and Comparative Biology meeting last January in New Orleans, however, I saw a great talk by Peter Zani from the University of Wisconsin-Stevens Point titled, “Daily emergence in crevice-dwelling lizards during winter is related to temperature, not light.” The study found that side-blotched lizards (Uta stansburiana) rely on temperature, rather than light, to determine if they should come out and bask while overwintering in rocky crevices. He described field observations and some very cool lab experiments that he’d employed to study overwintering physiology and behavior. These lizards from populations in eastern Oregon are active more or less all winter – if I recall, he claimed that he’d seen them out basking every month of the year except January (though the reason was most likely that he wasn’t there at the right time, not that they weren’t basking). This was a real epiphany for me, on par with the first time I was told that birds are actually dinosaurs. OK, maybe it wasn’t quite that mind-blowing, but nonetheless was an important shift for someone who thought previously of overwintering in reptiles and amphibians as a discrete state change where animals essential remained “off” until spring.
The past couple years, I’ve given a fair bit of thought to behaviour and energetics of overwintering in reptiles and amphibians (which I’ll write more about in a future post). And I’m excited to know that I’ll be working with some lizards for whom winter conditions, and their capacity to respond, are undoubtedly quite important to their survival and reproduction. And yet we know very little about this! With these questions in mind, we’ve kept the animals from our recent experiment and are currently hibernating them at 8 ºC in the labs at the CNRS in Moulis and Pic du Midi. I hope to begin next week measuring heart rates and metabolic rates to test for the effects of low-oxygen environments on lizard physiology during this state of low energy-demand. Look for some updates (hopefully interesting ones!) soon.
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