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I've been a Canberran since moving here from Adelaide on the first day of 1980. I now live in suburban Duffy with my partner Louise Maher, ABC 666 radio and on-line journalist. Among my early memories is following Sleepy Lizards (Shinglebacks) around the paddocks north of Adelaide, guarded by the faithful bull terrier. I have always been passionate about the natural world, trying to understand how it works, how the nature of Australia came to be, and sharing those understandings. My especial passions are birds, orchids and mammals. For much of my life I have been a full-time naturalist, running bush tours, writing books etc, doing consultancies, presenting a regular radio slot on local ABC, chairing a government environment advisory committee and running adult education classes. Recently I have eased back somewhat, but am still writing, teaching, doing some radio work and running overseas tours - as part of my fascination with our Gondwanan origins I've been running tours to South America for the past decade. I was awarded the Australian Plants Society Award in 2001 and the Australian Natural History Medallion in 2006, both for services to education and conservation.

Wednesday, 10 April 2013

The Blues: nature's trompe d'oeil #2

As promised in the last posting, I'm going to continue talking about beautifully blue animals and, as in our exploration of blue feathers, virtually none of the sky-coloured feet, beaks, skins, and insect parts that follow have any blue chemicals to thank for their hues. All are due to scattering of light by fine particles suspended in liquids, or by carefully ordered layers of collagen fibres, or thin layers of scales precisely spaced, or parallel ridges that reflect and emphasise blue light. The physics of most of it is beyond me I'm afraid - fortunately this is not a physics blog! However if you're mathematically minded, this might be of interest.

Bearing the general principles in mind, here is a tour of some of nature's blue bits.
Poison Dart Frog, family Dendrobatidae, Ecuador.
(Don't try this at home, or anywhere else, incidentally! Local people seem to acquire an immunity to these stunning but potentially deadly little frogs. I've heard of visitors getting very sick from handling one.)
Frog skin colours are very complex, with often three layers of different cells in the skin. In the case of blues, iridophores sit above melanin-filled melanophores; the iridophores reflect blue light back, like iridescent feathers that we discussed last time.
Reptile scales can be similarly constructed, to produce blues that can often be switched on and off by contracting the melanin cells below the light-scattering layers, especially in the case of displaying males.
Male Gippsland Water Dragon Itellagama (Physignathus) lesueurii, National Botanic Gardens, Canberra.
Unidentified skink, Cooktown, north Queensland. Any assistance gratefully received!
Male agamid, Queen Elizabeth National Park, Uganda.
Blue skin in mammals and birds is caused by arrays of collagen fibres, again above a melanin layer. I don't have pics of blue mammal parts (the best known of which are probably Mandrill faces and backsides, and the scrotums of Vervet Monkeys; oh well, I don't want to alarm your family filters anyway).
Southern Cassowary Casuarius casuarius, Wallaman Falls north Queensland.
(Taken through a car window!)
Blue-faced Honeyeater Entomyzon cyanotis, Griffith, New South Wales.
Blue feet are very popular in one bird made famous by wildlife documentaries. Here it's just the skin again.
Blue-footed Booby Sula nebouxii, Puerto Ayora, Galapagos.
The bluer the feet, the more attractive the owner to the only one who matters.
A bird's beak is covered with a thin layer of keratin rather than collagen; I can't find much about the role of keratin in producing blue beaks, but I see no reason why it wouldn't be a similar story to the collagen structures in skin.
Andean Ruddy Duck Oxyura jamaicensis, El Calafate, Argentina.

White Tern Gygis alba, Lord Howe Island.
Dusky Woodswallow Artamus cyanopterus, Canberra.

And of course there are numerous invertebrate examples.
Leaf Beetle, Chrysomelidae, possibly a cryptocephaline (the cylindrical leaf beetles) Whyalla, South Australia.
I have no idea about this beautiful chewer in particular, but in some blue beetles at least layers of disc-shaped scales in the cuticles are responsible.
(My thanks to Susan for helping with the family.)
In grasshoppers, the mechanism is apparently again a suspension of granules in the cuticle, above a dark background; I assume that this is how it works in this wonderful beast, but I don't know that it's been investigated.
Painted Locust Schistocerca melanocera Sierra Negro volcano, Galapagos.
Like so many other Galapagos residents, they are found nowhere else.
In dragonflies, the system is similar, with Tyndall scattering of light from particles suspended in a waxy layer above a dark cuticle layer.
Tropical Rockmaster Diphlebia euphoeoides, north Queensland.
Black-headed Skimmer Crocothemis nigrifrons, Canberra.
And of course numerous butterflies and moths flaunt blues, with a variety of variations on the themes described above, involving precisely spaced layers of scales. Some members of Papilio and Graphium swallowtails actually do have some rare blue pigments, but even these are emphasised by scale orientation.
Shining Oak Blue Arhopala micale, Cairns, north Queensland.
Satin-Green Forester (Pollanisus viridipulverulenta, Yeldulknie Conservation Park, South Australia.
Its iridescence makes it flash from green to blue, depending on the angle. Don't sniff too deeply - its family, Zygaenidae, specialises in releasing cyanic acid in self-defence!
(My thanks to Susan for putting me on the right track to identifying this one by recognising the family.)
Urania Moth, Manu National Park, Peru
Euchromia creusa, north Queensland. Here the blue is not (mostly) in the wings, but in body scales.
Presumably the principle is the same however.
Finally, to a couple of animals which probably do have pigments - many marine animals do, including crustaceans, and I see no reason why these crabs would not.
Sally Lightfoot Crab Grapsus grapsus, Galapagos.
Soldier Crabs Mictyris longicarpus, Cullendulla Creek Nature Reserve, New South Wales
Well I'm about blued out for now, but I've enjoyed the journey; I'd love to hear if you have too, or if you have any comment to make. We're still to talk blue in plants, but we might have a break from blue before we tackle that one.

EITHER WAY, BACK SUNDAY





4 comments:

Susan said...

Your beetle looks like a leaf beetle Chrysomelidae, the South Australian moth like a burnet Zygaenidae (although I don't know if this family occurs in Australia). The technical term for the waxy coating on odonts, as I am sure you know, is pruinescence (as in the powdery waxy coating, or 'bloom', on plums).

Ian Fraser said...

Thanks Susan; I've followed up both those suggestions, found good corroborating evidence and updated the post accordingly (with appropriate acknowledgement, of course!). I panic about beetles; I really should have recognised a chrysomelid.

Swan Pond said...

Great post. Those blue feet are amazing. The Argentine duck looks a lot like the Aussie Blue Billed Duck don't you think? Am looking forward to when you'll have time to cover pink!

Ian Fraser said...

Hello Swan Pond, and thank you for taking the trouble to comment. I should have said, but the Andean Ruddy Duck is very closely related to our Blue-billed - same genus. Thanks for pointing that out. Yes, the BFB's feet truly are amazing; you must visit them some day. And I'll get to pink, I promise!