Today's guest poster is Dr Christofer Clemente. After postdoctoral stints at Cambridge and Harvard, Chris obtained an ARC DECRA and joined the Wilson lab at UQ. You can keep up with Chris's adventures on his science blog, Biomechanics Downunder.
I have long been impressed with the ability of the South American Basilisk lizard to run on water. There are plenty of videos of it on youtube, that show 2 important aspects of its locomotion:
- it's able to lift the whole body out of the water, and
- it's able to do so for quite long distances (around 10-15m).
Some lizards' ability to run on water has been documented quite well by a series of papers by a group at Harvard University, particularly Tonia Hsieh. They've done some great work, including describing how smaller lizards are better able to support their body weight than are larger lizards, modelling 3D forces andrecording 3D kinematics of the lizards' stride. Below is a gif showing some of the detailed kinematics of the lizard stride from George Lauders lab webpage.
(NOTE: just click on the gifs if they are not running)
One other important point reported in these papers, based on the description given in Hsieh (2003), is it seems the lizards' kinematics change when running on water, such that the limb moves behind the hip, rather than being both in front and behind the hip.
This is shown quite well in the gif above. So given this information on how Basilisk runs on water, we can then ask the question, Can the water dragon (Intellagama lesueurii) also run on water?
I was led to believe it may be able to from two dominate and convincing lines of logic.
- they are water dragons! - it might behoove them to be able to do so and
- I heard reports of the juvenile lizard being observed doing so from a fellow researcher.
So I modified the lizard racetrack which I have here at the University of Queensland, by placing a short, water-filled aquarium across the water dragons' path which they must cross to get to the other side. Then I sat back and filmed them using the fastec high speed camera system. And this is a typical (read: absolutely best) result below
Well the first thing I noticed is that they are no basilisk lizards. The body is not held out of the water and progress is significantly slowed. The first step seems hardly effective at all, and the second step is much deeper, and seems like a breaking step, with the foot held flat. However, the following step seem to have some similarity to those of the basilisk. From steps 3 onwards, the foot does not appear to be pushed as far forward, and much of the stroke seems to be posterior of the hip, as in basilisk. Secondly the trapped air bubbles on the foot are interesting, and these are also observed for basilisk, where they are thought to be the result of tiny fringes along the toes of the south american lizard. Such fringes however, are not obvious in the water dragons. Below is a snapshot of the bubble being dragged down on the trailing edge of the foot.
So I'm unsure what to make of this all. It does look like they are capable of some run/swim locomotion, but it certainly falls short of the amazing prowess of the basilisk.
Here are some less impressive runs. Though notice that the right hind foot is actually brought out of the water - suggesting they could be using surface effects to give more downward force.
And this one below shows a similar stroke.
So that's as far as I've got. Let me know whether you think it is sufficiently interesting to warrant detailed kinematic analysis, or whether you think water dragons are just a little impaired when it comes to running on water.
Finally, I leave you with what happens after several trials and the dragons know the water is coming up. It led me to believe, that for water dragons, they sure do not like water!