Friday, 19 July 2013

Jumping beans in Slow motion

Between 2010 and 2012 I worked at the Rowland institute at Harvard university. Most of my time was spent researching the muscular dynamics of frog muscle, by building robotic frogs, but every now and then we liked to goof off scientifically. That chance came the one day when the head of my workgroup, Chris Richards, brought in a mexican jumping bean. Being from Australia, I had not seen one of these before, and that is sad. Cause they are friken awesome! The bean itself is the seed of a shrub, the genus Sebastiania. Inside this bean is growing the larve of a little brown moth (Cydia deshaisiana). The moth makes a hollow inside the bean, as it eats the bean from within. But what makes it amazing is that it is able to thermoregulate by moving the bean from hotter places (such as in the sun) to cooler shadier places. It does this by 'jumping' - hence the name. The actual mechanism of how this tiny moth can get the whole bean to jump is unknown, and would probably require some xray cinematography, which sadly we didn't have at the institute. What we do have though, is the next best thing, very sensitive force plates and high speed cameras.
Having several dead lines to attend to, i decided the best use of my day, would be to ignore them all and play with the little bean. I set to work on it, and this is what i got out.

First i was interested in the amount of ground force the little bean is capable of producing. I used a honeywell force cell to measure it, jumping up from a smooth plastic surface. The force plot is show below.

Here the x-axis shows time in ms and the y-axis shows vertical force (in newtons). Peak force was about 0.14N. The body weight of the bean (both worm and seed) was 0.134g therefore, this bean was jumping with a force over 100 times its body weight!!

The second thing i noticed in my force traces is there was a smaller first peak, followed by the major peak, about 500 ms later. This was present in almost all of the force traces i got.
I decided to use the photron high speed camera (photron FASTCAM SA3 model 60K-M2) to take a look at what was going on and this is what i found. The film is taken at 1500 fps, and is slowed down 60 times.

The first peak on the force trace does appear obvious in the movies as a little shuffle backwards, before the main jump. My guess is that the bean is shifting its position inside the shell in preparation for the jump (possibly storing energy) then shifting weight quickly causing the bean to jump up.

Can the water dragon (Intellagama lesueurii) run on water?

Can the water dragon (Intellagama lesueurii) run on water? 

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, for example a short one here. 

Its pretty amazing. Looking at this video alone shows as two important aspects of its locomotion, 1) it is able to lift the whole body out of the water, and 2) it is able to do so for quite long stretches (around 10-15m). This ability has been documented quite well by a series of papers by the group at Harvard University, particularly Tonia HsiehThey have done some great work, including describing how smaller lizards are better able to support body weight than larger lizards , modelling 3D forces and recording 3D kinematics of the lizards stride. Below is a gif showing some of the detailed kinematics of the lizard stride which i stole 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 kinematics change when running on water, such that the limb moves behind the hip, rather than being both infront and behind the hip.   

"whereas the hindlimb kinematics of other lizards on land are typically symmetrical (i.e. limb excursions anterior to the hip are of similar magnitude to the limb excursions aft of the hip), basilisks running through water exhibit much greater excursions aft than they do anterior to the hip. "

This seems to be 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 also run on water? 
I was led to believe it may be able to from two dominate and convincing lines of logic. 1) they are water dragons! - it might behoove them to be able to do so and 2) 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 their 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 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 am unsure what to make of this all. If does look like they are capable of some run/swim locomotion, but it certainly falls short of the amazing prowess of the basilisk. These juveniles tend to avoid the sinusoidal swimming pattern, with tucked in arms, as seen in adults. Though the top view does appear to show that this is still employed, in conjunction with the feet, suggesting that this is indeed a uniquely adapted form of locomotion. 

Here are some lesser impressive ones. 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 is as far as i have 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 retarded 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!