A redesign of the original asymmetry contraption has finally reached (hopefully) it's perfected state. With a black felt backing I was able to take several test pictures in the '99 Garden South with the assistance of Dr. Andrew McCall.
With a contraption built to take accurate pictures of flowering Echinacea heads, I assumed that fluctuating asymmetry (FA) measurements were just around the corner. Boy howdy was I wrong. It turns out, as Stuart has informed me, there are many ways in which to measure FA, each as viable as the next. The most apparent idea, though potentially most flawed, was to simply measure the length of each ray floret and compare that to its complementary floret directly across the disk. Measuring 2 pairs of florets per head seemed simple enough, though it was soon found that there are many problems with such a simple procedure. For example, this idea doesn't take into account any herbivory/senescence that has occurred, though most methods don't. Also, any difference in widths between the florets was ignored. This plan obviously had to go. The quick fix solution to this was to measure the width of each floret as well, and compare these numbers separately. This again causes problems, since it doesn't take into account the varying shapes of individual florets, but rather the similarity of a total area. The florets can have a similar area and yet certainly be very much asymmetric.
The ultimate solution to these problems is to measure asymmetry with an all encompassing measurement rather than one that attempts to isolate single florets. Stuart suggested creating 2 circles of best fit; one around the ray florets and one of the disk itself (either the outer edge or the flowering anthers, both may present their own difficulties). These circles would each have its own center point, the disk circle would represent the "true" center of the head, while the ray center point would be altered by any asymmetry of the florets. The ray floret center point would be calculated based on the area of color, therefore taking into account the area of the floret without making any assumptions as to the shapes of individual florets. The difference between these two points would give a numeric value of asymmetry. It seems to be the best solution so far, but I'm open to any other suggestions. This plan, like the rest, definitely has its own problems.
In non-Echinacea related news, the chiggers continue to molest my legs, but have also (oh, so fortunately) moved onto the rest of my body. I now have a collection of bites that range from that spot between my shoulder blades that I can never reach, to inside my belly button, to the tops of my feet. Sure glad those suckers are small enough so I can't see them sneak into all of my clothing, yet large enough to cause so much damage. I'll keep you posted on how my itching develops.
Dear flogophiles:
I'm trying to devise ways of measuring FA (see previous post) on our plants. Ideally, we would want measurements on several different organs or parts because if, for example, inbred plants are more developmentally unstable, it would be more convincing if they were more asymmetric in both leaves and inflorescences.
Colin is designing (and hopefully testing) the picture-taking rig for flowering heads. But, I think that it can also be used to take pics of leaves. The trick is getting the leaf to lie flat on the backing of the rig. I was thinking of buying a hand-held scanner to scan leaves in the field, but that takes 4-8 seconds per leaf, and it seems easier and quicker to just snap a picture. Also, I am not sure where measurement error would come from if you scanned the actual leaf.
My biggest concern is getting the inflorescence to lie flat on the rig backing. It is important to get the ray florets nice and flat against the backing or else you could be mis-measuring things pretty easily. I almost think it may be easier to actual measure the ray florets using calipers in the field -- it would certainly be more accurate but would also take a bit longer, and you couldn't really measure ALL the ray florets per head -- it would take WAY too long.
If the rig doesn't work, we could have three people go out with calipers, one after another, measuring the same heads and leaves per plant. You could only measure perhaps 4 ray florets per head, but this is probably OK. This could probably be done in one day! If we could get a pendragon form for this measurement, it would be great, too. So, then you would have the measurements, as well as error that could be assigned to individual observers.
One more thing: We can measure asymmetry in the actual inflorescence by measuring the length of the ray florets, but we could also measure asymmetry WITHIN each ray floret, by measuring the L-R sides. This is what has to be done for the leaves becuase they are naturally asymmetric about the stem of the plant anyway due to differences in leaf age.
OK, my thoughts for now. Things are very exciting here, I hope to get my batteries in the next 2 days so that we can get the cameras up and running by Sunday. Science is happening!
Andy McCall