Friday, 25 January 2008

Colour and Convergence


A group of small moths with similar brown and yellow colour pattern

Colour & Convergence

Here is an array of moths all collected at the same light sheet in the rainforest over a few months time. They all bear similar colour patterns but are from a number of families. We see the following families in the photo above: Pyralidae, Oecophoridae, Tineidae, Tortricidae, Arctiidae and Cosmopterigidae. Ted Edwards points out that other families with some species with similar yellow/brown colour patterns are: Xyloryctidae, Lacturidae, Noctuidae, Psychidae, Heliodinidae, Lecithoceridae, Gelechiidae, Hypertrophidae and Adelidae. He further notes that one theme is present in these moths is that they are all small. No similar colour patterns have been found in moths of the families noted that have large species such as the Noctuidae (cutworms), Pyralidae or Arctiidae.

This yellow/brown motif is clearly a form of convergence. Convergence occurs when unrelated organisms independently acquire similar characteristics. This suggests that there must be some advantage to looking like this. But what is it? It is obviously a form of disruptive coloration. Simple disruptive coloration is defined as a visual disruption forming a pattern that does not coincide with the contour and outline of the individual. But the patterns of these different moths are slightly different one to another. Could the brown and yellow look like a sun spot on a leaf? Or could it serve to camouflage the moth on a tree trunk or a piece of bark by disrupting the wing shape? I can’t answer these questions because as often as I have seen these moths at the light sheet, I’ve not seen a one of them during the day in their natural habitat. Perhaps, an Honors or a Masters project is beckoning…..

1 comment:

Janet Grevillea said...

I am interested in the tiny yellow and brown moths. Recently there was one sitting very still on a Spotted Gum at our place. Its colours did not blend in with the bark, but it was difficult to see because it was so small and still. As far as I can tell from various guides it was a Manulea dorsalis.