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Rot

21 Mar

Rot

Timber from a beech tree infected fungus inspired my inlay of an albatross gliding over the vast southern oceans.

Many fungi cause marbling, mottling and discolouration in timber, and whilst this rot may detract from the structural value of the wood, the ‘spalting’, as the patterning is called is much sought after by wood turners and knife handle makers. This discolouration was probably produced by ‘white rot’, which is caused by a common polypore fungus called Trametes versicolor, the ‘turkey tail’ bracket fungus.

Trees, like humans, gain character (and a huge disease load) with age. Beech trees, in particular, are prone to fail suddenly – huge limbs dropping off in a storm, or entire trees keeling over – due to the insidious activity of the fungal hyphae literally eating the tree’s heart out.

Yet, in so doing, we are sometimes left with something which is ‘more’ than the unaffected original. It is as though the humble process of rotting has wrought a truly beautiful transformation.

The albatross is sometimes used metaphorically to mean a psychological burden or curse from Coleridge’s ‘Rhyme of the Ancient Mariner’. I have always thought of them as truly unburdened in their wandering, effortless and epic flights.

I doubt there are fungi in the sea (bacteria do the rotting there), here is an escape from rot.

Thigmotaxis

1 Jan

Centipedes, like many other small creatures exhibit a curious behaviour called thigmotaxis – they like to squash themselves into corners in order to maximise body contact with surfaces.

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This is a common brown centipede resting against the side of a plastic sandwich box.

The reason small soil dwelling creatures do this is because they are particularly vulnerable to changes in humidity, they dry out quickly, or become water logged. The behaviour is so overwhelming that it can mask other reactions to external stimuli such as vibration, chemicals, etc..

Years ago I spent long hours studying the behaviour of Lithobius forficatus L. (the common brown centipede) as a Ph.D. student in order to discover what the beautiful structures on its hind legs were for:

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This is a diagram of the underside of a male centipede. You can see that the fattest segments of the last four pairs of legs, closest to the body, are equipped with a row of interesting pores. These are the coxal pores. Under the pores lies a curious tissue, known as the coxal organ.

You can see the pores more clearly here:

Coxal pores dimensions

At very high magnification the organ looks like this:

LM coxal pores

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Under the electron microscope the cells look for all the world like ‘kidney’ or ‘malpighian tubule’ (insect kidney) cells. On this basis it was classified as a ‘typical transporting epithelium’, a not very helpful description as we had not a clue what might be transported.

The Behavioural experiments proved compelling and, using a circular choice chamber to get around the centipede’s natural tendency to flatten itself to a wall I was able to demonstrate that the coxal pores were responsible for releasing a sex hormone, or pheromone attractive to members of the opposite sex.

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I came to the conclusion that the main problem facing centipedes (and anyone living under ground) was not drying out, but becoming water logged. So the coxal organ is most probably very good at getting rid of excess water (centipedes living in xeric or dry habitats have very small coxal pores, or none at all), and in so doing chucking out a useful ‘come on’ signal to other centipedes of the same species. The pheromone chemistry is phenolic and related to the chemistry of centipede cuticle (hardly surprising given that the coxal organ is modified cuticular epithelium which normally secretes the centipedes exoskeleton).

Sticking closely to a surface is not my thing. I prefer to venture out and discover things anew. Multifunctionality is common amongst amongst biological systems – it is the stuff of evolution and natural selection: a hand becomes a wing (pterosaur, bird, bat); a wing becomes a diving tank (Great Diving Beetle’s plastron); a zoologist become a woodworker…… A close study of centipede backsides was instructive in beginning a small voyage of discovery for me, a gift by a true mentor J.Gordon Blower, the ecologist and millipede man who pointed them out to me whilst smoking a number 6 filter tipped in his nicotine stained lab way back in 1979.

JG Blower 1

I have always thought the phrase ‘there is no need to re-invent the wheel’ the dullest of aphorisms. Re-invention is human, discovery and rediscovery a divine gift. Get out there and look at something very small, or something very big, but please do go and look, because your discoveries will be unique.

PMH Littlewood. Fine structure and function of the coxal glands of lithobiomorph centipedes: Lithobius forficatus and L. crassipes (Chilopoda, Lithobiidae) 1983. J. Morphology  Vol 177

PMH Littlewood. The chemosensory behaviour of Lithobius forficatus. 1. Evidence for a pheromone released by the coxal organs (Myriapoda: Chilopoda).Journal of Zoology Vol 211 January 1987

PMH Littlewood and JG Blower. The chemosensory behaviour of Lithobius forficatus. 1. Evidence for a pheromone released by the coxal organs (Myriapoda: Chilopoda).Journal of Zoology, Vol 211, 1987

PMH Littlewood.The water relations of Lithobius forficatus and the role of the coxal organs (Myriapoda: Chilopoda).J.Zoology, Vol  223, 1991

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Speedster

31 Mar

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We found this little beauty on the wall of a converted 13th century chapel in a tiny fortified village called Cotagnano in Northern Italy on holiday one year. It is the centipede Scutigera coleoptrata – a most impressive arthropod which has been around, unchanged, since before the evolution of insects. Each of its fifteen pairs of legs is slightly longer than the set in front, this is because of the way it runs. It is the fastest arthropod on land. I have seen a captive one catch three blue bottles and subdue them with its poison claws in the blink of an eye, holding each paralysed prey item, conveyor belt like, beneath its body ready for a blue bottle buffet.

Sprinters have to adopt a particular ‘gait’ in order to propel themselves quickly across the ground. They aim to have their propelling foot in contact with the ground for the shortest time, the return phase being much longer than the propulsion phase. Think of a galloping horse – the legs appear to remain airborne for longer than they are in contact with the turf during a gallop. The very opposite is true in a tug of war, or scrum, where the propelling foot stays on the ground the maximum length of time and the return step is very quick – this gait provides maximum traction.

Scutigera runs so quickly that each hind leg over reaches the legs in front – hence the raked appearance of the appendages along the body. Unlike any other centipede, Scutigera also possesses compound eyes and is, therefore, very sensitive to movement in its visual field. It has a respiratory pigment and unusual dorsal spiracles leading to trachea or breathing tubes – feeding a relatively high metabolic rate. This centipede is the arthropod equivalent of a Cheetah.

Humans have for centuries tried to emulate Nature in the search for engineering perfection, speed and power. We can only admire this centipede’s level of pure biological sophistication it seems to me. It is astonishing to imagine how, in the space of a few million years of evolution, Natural Selection, working on the unlikely substrate of the segmented body of a marine invertebrate could have produced this miniature speedster.