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Pondering on the glorious wonders of nature

by
01 October 2016, at 1:00am

Dr David Williams stops to consider the ways in which humans and other species see things and the wealth of information that is instantly available

SEASON OF MISTS AND MELLOW fruitfulness, close bosom friend of the maturing sun... well it will be autumn by the time you are reading this, but at the time of writing it’s still the middle of August – I’m ahead of myself for once! 

No mists at the moment for sure but the mellow fruitfulness is here a bit before time, I seem to think. My perambulations through the fields around our village are punctuated with ripe blackberries. All ready to be eaten by squirrels and birds to have their seeds spread near and far.

So if you wanted to be eaten by such foragers, wouldn’t you want to be a bit brighter? It turns out that these berries have a waxy sheen that reflects radiation in the ultraviolet spectrum. So for birds and rodents that are able to see in the ultraviolet, Rubus fruiticolor isn’t so much the blackberry as the bright berry!

We like to think that as humans we are at the top of the evolutionary tree, don’t we? With trichromatic vision, we see in red, blue and green while most mammals just see using two cones, dogs in mauve and yellow, quite whatever that looks like! But actually there is a huge world of colour out there that we are missing. 

The birds not only see blackberry berries as all reflective while their leaves are dull in UV, they also use those short wavelength rays in sex selection. To us the chaffinch looks as if he has a plain white patch on his cheek, but actually that’s a UV reflective area and the fitter the bird the brighter the reflection.

If you’re a rodent your wee is UV reflective. I’m not sure how that helps you as a mouse, but for a kestrel hovering overhead an ultraviolet wiggly line signals a track frequented by prey items.

You probably know that a simple yellow flower like a buttercup actually shows up with radial lines on its petals in ultraviolet light – as it would be seen by a bee which also has a brighter visual world than we do.

Butterflies use signals in the ultraviolet range for mate selection but also in determining what time of year to start their migration, at least in the case of Monarch butterflies in the States. Once they are on the move though, they use a feature of light completely invisible to us – it’s polarisation.

Monarchs y from their summer breeding grounds in northern North America to overwinter in Mexico and navigate back and forth using the polarisation vector of the sunlight to show the way.

Bees, crickets and ants also use the sky’s polarisation compass for navigation too. And once you start investigating, there are insects that use polarised light for mate choice as well. I guess once you have evolved a photoreceptor that can detect the polarisation of a light wave, you might as well employ it in as many ways as possible!

Insects do have to communicate with lesser vertebrate beings too, of course, not using ultraviolet or polarisation but the simple colour spectrum we vertebrates have to use. So today I noticed the amount of ragwort all beautiful shining yellow around the edge of the fields I walk through, with a closer look revealing the black and orange caterpillars of the gloriously red-hued cinnabar moth.

Truth be told I’ve seen the plant every time I’ve walked that way, but today noticing it led to a few questions. First of all, why is the ragwort poisonous? Yes I know – it’s got pyrollizidine alkyloids in it, we all learnt that at vet school.

But what is their purpose? Presumably to stop animals – horses and cows for sure but also insects – from eating the plant. But if that’s the case, then why is the cinnabar moth caterpillar so attracted to the plant, indeed making Jacobaea vulgaris the ragwort its preferred food source?

It’s only when it’s dried in hay that ragwort loses its nasty taste, but obviously cinnabar moth caterpillars have got over the nasty taste and also the toxic nature of those alkaloids. Indeed, ruminants aren’t affected either, not because their livers are resistant to the toxins but because rumen bacteria detoxify them.

Apologies if you all know that, but having done ophthalmology for the past quarter of a century I have forgotten most of the detail of ruminant physiology and toxin biochemistry I was taught then, if ever I knew it in the first place. And one might ask whether we really need to know that in the first place!

Easy access

It’s all there at the click of a button or the scan of a mouse, isn’t it? Rather different from the 1980s when if it wasn’t in the textbook the only way of searching the literature was to work one’s way through the foolscap green volumes of Index Veterinarius for each year. These listed each paper published in the key veterinary journals that year. You knew you had completed your literature search when all the papers referenced in each article were already in your list.

It might take weeks to complete a full literature review. And now a few minutes online will give you a pile of papers to read. But maybe that’s the problem. If it takes hours and hours over days and weeks to piece together the information one needs, then each paper is read and pondered over before the next can be searched out from the dusty library shelves and perused or maybe photocopied for future reference.

Now there is so much information out there, available at the mere touch of a button, click of a mouse, that to my mind one soon feels overburdened by it.

Thank goodness for Wikipedia! Or Wickedpedia as I’ve heard some academics call it. Far too easy for students to get an overview with who knows how many errors in it?!

On the other hand, if I produce a book with an error in it – you’ll find a grave omission of avian inherited glaucoma in my book Ophthalmology of Exotic Pets for example – the only chance I have to correct that is at the next edition, if I get round to producing one. But in Wikipedia a reader can immediately note the omission and it can be corrected.

So I must admit that the online encyclopaedia is my first port of call if I have a question about ragwort toxicity, blackberry antioxidants or butter y migration. And there, you thought that all you’ve just read was stored away in my head did you? Dream on!