The Lizard Log

The Langkilde Lab in Action

On Clines. And Victorian Men.

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I really love reading books about early ecologists–or naturalists, as they were often called in the late 19th century. They have eventful maritime adventures and discover a wide variety of new exotic species. These young naturalists are always depicted as noble and inquisitive and have a much better sense of morality than their overly eager captains who are usually related to them. Okay, perhaps I read about fictional naturalists* more than the actual naturalists who shaped the field of ecology…which is kind of a shame, as the real ones were just as interesting! Darwin, Wallace, Hooker (and so many more!) are all pretty rad. Some of the early ecological and biogeographic  principles these early naturalists cooked up are still being tested–and, more often than not, supported–today.

Alfred Russel Wallace (Left) and Joseph Hooker (Right) looking dashing in their Victorian way.

Alfred Russel Wallace (Left) and Joseph Hooker (Right) looking dashing in their Victorian way.

Take, for example, Bergmann’s rule, which describes the latitudinal cline we find with body size: in general, organisms of a particular type are larger at higher latitudes where it is colder and smaller at lower latitudes where it is warmer. Bergmann suggested this is because large animals have a larger surface-to-volume ratio and thus less relative surface area over which to lose heat. This trend is common in birds and mammals, though of course there are exceptions. There is a similar cline with limb length and latitude (Allen’s rule – animals have smaller limbs in colder climates, in theory for similar reasons).

If you’ve made it this far, you’re probably wondering what this has to do with our lizards. Well, it is thought that there is a latitudinal cline with an animal’s baseline level of stress hormones. Some of our research, however, doesn’t seem to support this cline. Lizards at sites with fire ants have higher baseline levels of stress  hormones…which means we actually see the opposite of what this cline would predict!  One of the goals of our first trip this year was to collect blood samples from lizards at additional sites across the south (with and without fire ants) to help us parse out what’s going on. Chris and one of our undergrads will also be collecting blood samples from lizards in Pennsylvania and New Jersey to give us a much broader range of latitudes from which to consider this cline.

That meant covering a lot of sites in short time. Whew! It didn’t help that some of our sites weren’t as active as usual. One of our Tennessee sites has seen so much rain lately that the usual lizard sites were covered in over a foot of water!

Edgar Evins under water

Edgar Evins under water.

Still, Sean, Chris, and I managed to collect blood samples from enough lizards to keep our sample sizes happy…and we even managed not to kill each other while hotel-hopping across the south for 10 days! Success!

We caught a nice lizard on a tree at St Francis National Forest (AR). This timber rattler was waiting at the base.

We caught a nice lizard on a tree at St Francis National Forest (AR). This timber rattler was waiting at the base of that tree.

 *For an interesting read, check out The Voyage of the Narwhal by Andrea Barrett. It has nothing to do with narwhals, but rather follows a young naturalist and his soon-to-be brother-in-law on a journey to the Arctic and back. It takes a weird turn about halfway through, but it’s still pretty interesting.


Author: Gail McCormick

Science writer at Penn State University; papercrafter, ecologist, theatre-lover.

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