Colin Donihue

As I’ve mentioned before, one of my primary research interests is how these lizards change in different contexts. So far I’ve measured a whole lot of morphological traits like limb length and head width on lizards from islands all over the cyclades. I’ve also measured a whole-organism performance trait, namely bite force, which relies on many of these head-related morphological traits working together in concert to see if that varied from one island to the next. Head measurements have differed significantly, as have bite force measurements. Now I want to determine whether the differing limb lengths also result in differences in performance, specifically sprint speed.

There are many ways in the literature to measure lizard sprint speed. The most common is to use a racetrack or small treadmill, set a lizard down and record how fast it runs across the surface. This works well, to a point, but I’ve never been entirely satisfied with papers discussing the implications of a lizard that runs 4% faster than another over a thick rubber mat. I wanted to test sprint speed in a more realistic context. My first thought was to build a fenced course out in the field, but I soon realized that wasn’t going to be feasible, so I set out to replicate field conditions in the lab.

The two populations I most wanted to test were both from Naxos. One lives in a highly developed valley full of rock walls and terraces and spends almost all of its time on and near the stones. The other lives in an area without any significant human land use – no grazing and certainly no walls, and so spends its time running across loose sand from bush to bush. These two substrates formed the basis of my question – because the lizards in the two areas have different limb lengths, does that mean they have different sprinting capacity over the substrate they’re most used to traversing?

So, I built a 3 meter long plastic-lined chute in the lab. I covered the bottom with sand, set up my video camera, and started recording lizards from both populations running across it. Things got really interesting when, after I absconded with about 15 large stones from an old rock pile, I built a mini rock wall in the chute. I then re-ran all of the lizards across the stones to see if some managed better than others. I now have a few hours of video to go through, frame by frame to calculate the sprint speeds of each individual, but fingers crossed something interesting comes of it! Here are a few pictures of the set up.