Iridescence

Last Thursday I had the pleasure to host Dr. Heather Whitney of the University of Bristol for a seminar titled: ‘Slip, grip and invisible iridescence: insect interactions at the plant surface.’ It probably requires an explanation why an evolutionary microbiologist came to invite a plant biologist (neither working on plant-bacterium interactions). I have published some posts a while back on rock pooling (e.g. here) as I am originally a marine biologist and Cornwall has rekindled that flame. A while back I even started a blog devoted to rock pooling and keeping local animals and seaweeds in the aquarium (to the detriment of this blog…): An Bollenessor, which means ‘The Rock Pool Hunter’ in Cornish. One local organism that has particularly gripped me is the Bushy Rainbow Wrack Cystoseira tamariscifolia, which is bright blue, purple or green when viewed under specific angles. I found out that this process is termed iridescence, where color is produced not by ‘dyes’ but purely by the physical structure of materials (as do the ridges on a cd for example). First a picture of the Rainbow Wrack in the aquarium and then one in a rock pool at Castle Beach, Falmouth:

IMG_1966IMG_3293Quite stunning as you can see! Some googling brought me to Heather’s research page and I sent her an email to ask her if she knew about these beautifully iridescent seaweeds. Although she was aware of iridescence occurring in some seaweeds, she did not know about such a striking example, especially not in the UK. She therefore made the trip to Falmouth to have a look herself and also do some collecting to take a closer look at the microstructures using electron microscopy back in Bristol. In her seminar, Heather talked about the structural biology underlying iridescence in plants and its effects on biotic interactions using some very cool bee experiments. However, the adaptive value of iridescence, attraction, camouflage, photosynthesis or it simply being a byproduct of surface structure, remains largely unresolved. Hopefully, Heathers future work on the Rainbow Wrack will shed more light on this cool phenomenon!

Michiel

Iridescence occurs in plants (vascular plants, ferns, worts, seaweeds) and of course animals (e.g. peacocks and the morpho butterfly), but also in some bacteria: see here for a very nice blog post.

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