No, don’t be ridiculous
Seems unlikely, doesn’t it? On the departing trolley the jellies enticingly wobble, cheese has been massacred, wine glasses (all six of them) drained, so it’s time to release a very gentle burp, loosen the braces an inch and re-engage one’s startling attractive neighbour as to the finer points of cooking seppie – only a certain sort of ink will do – and the vexed question of whether to go for a decent white Loire, look to the Burgundies and settle on a cracking Meursault, or intriguing thought maybe a Jurançon? So unless one suffers from a serious eating disorder or are cultivating a colony of tape-worms, the combination of the laden table and convivial companions is a bench-mark of human enjoyment. Come to think about it, wasn’t there that chap on the eastern fringes of the Roman Empire who was very keen to ensure there was enough wine to go round and kept on talking about banquets beyond our wildest dreams? Feeling peckish?
Yes, of course
If the principle of dinner revolves around the fact that whatever is on the plate doesn’t have a say in the matter, then in the wider world large, slow-moving animals with acres of exposed flesh would seem exceptionally vulnerable. Think of that marine creature the sea-hare (Aplysia) that although a close relative of the garden snail does not even have a shell. Everybody wants a bit: crustaceans, fish, even sea-anemones. But look what happens if interference progresses from an experimental nibble to some decidedly rough handling, say by a spiny lobster. Suddenly the sea-hare releases a purplish cloud and the would-be attacker is in trouble.
Ingeniously the sea-hare possesses two sets of glands and these respectively release ink and a separate opaline secretion that on contact with sea-water immediately becomes extremely sticky. Either working together or independently these products provide an impressive battery of defences. The billowing cloud can act as a smoke-screen, while the ink itself tastes disgusting. Watch the opaline secretions swing into action as they clog the receptor structures that the lobster uses to detect potential dinner. But there is more. The opaline secretions are laden with free amino acids that are an important cue for food. The lobster is completely fooled and starts to try and feed on the swirling cloud as the sea-hare slips away. It is deceit at its best and goes by the name of phagomimicry: you feed and feed yet remain hungry.
It all depends on the question
Sea-hares aren’t the only animals to use ink. Artists such as Samuel Palmer and David Friedrich Caspar turned to sepia ink to capture slumberous landscapes, while cooks extol the delights of seppie. Cuttlefish are the ingredient and along with their relatives the squid they produce ink. In common with the sea-hare they employ two secretory glands, albeit of completely separate origin. Forming a deceptive cloud is one result, but by being unpalatable it also provides a chemical deterrent. That the ink appears not to be phagomimetic is less surprising. This is because by the time the attacker has investigated the cloud hanging in the water the potential victim has jet-propelled its way over the horizon. And perhaps not entirely unrelated is a link to rocket fuel. Most propellants depend on mixing two chemicals, say kerosene and liquid oxygen, to provide an extremely energetic reaction.
The bombardier beetle has achieved something remarkably similar by the expedient of having two glands that by combining a mixture of hydroquinones and enzymes (oxidases) produces rapid pulses of a scaldingly hot blast that is skilfully aimed to deter any would-be assailant. Which brings us full circle to the sea-hares. The bombardier beetle relies on a very rapid combination of the two mixtures, but in effect this is what also happens in the sea-hare when the ink and opaline secretions mix but now in slow motion. The basics, however, are much the same because with the sea-hare they involve an oxidase (known as escapin) in the ink that reacts with amino acids (mostly lysine) in the opaline secretion. One product is the highly reactive hydrogen peroxide (H2O2) that is another arrow in the quiver of the sea-hare’s armoury.
Be it sea-hare or beetle their attackers leave hungry. Deceit, however, comes in all sorts of shape and form and none more so than the sexual arena. As this is biology we won’t consider starlets but cockroaches: Not only do the females lactate, but at the start of the whole business boy has to persuade girl – who admittedly is leaking pheromones all over the place – that it is very much in her interests to proceed. The lure comes in the form of secretions provided by the male that true to form the female avidly laps up. The overall nutrient value is negligible but cunningly not only does the exudate contain pheromones but like the opaline secretions of sea-hares is very rich in cheap amino acids that persuade the female that she is at the equivalent of a candle-lit dinner. Insects like crickets have also learnt to dole out cheap goodies to the females in the form of nuptial gifts and such phagostimulants support the so-called Candymaker Hypothesis. I thought that would interest you: by the way are you free for dinner?
Text copyright © 2015 Simon Conway Morris. All rights reserved.
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