Fluctuating Asymmetry?

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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.

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Why not measure the L-R width of the florets along the entire head? This would match the method I'd like to do with the leaves. Of course, you would still have the problem with florivores causing misshapen heads.

Andy McCall

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