By Vladimir Brezina
This week’s Photo Challenge has got me thinking about the color Purple.
The most vivid purple that I’ve ever seen was not the purple of flowers, nor of sunsets. Rather, I see it in my lab. One of the experimental animals we work with is a large marine slug from California, Aplysia californica, popularly known as the sea hare. When disturbed, the sea hare releases a cloud of ink that has the most intense, rich purple color.
Those of a classical bent will recall Tyrian Purple, also known as Royal or Imperial Purple, a dye greatly prized in antiquity, which was made from a similar ink produced by several Mediterranean snail species:
Tyrian Purple was expensive: the 4th-century-BC historian Theopompus reported, “Purple for dyes fetched its weight in silver at Colophon” in Asia Minor. The expense meant that purple-dyed textiles became status symbols, and early sumptuary laws restricted their uses. The production of Tyrian purple was tightly controlled in Byzantium and was subsidized by the imperial court, which restricted its use for the colouring of imperial silks…
Interestingly, the purple color of the sea hare’s ink, as well as the purple tinge of its skin, actually derives from its preferred diet of red seaweed. If sea hares in the lab are fed green seaweed, their skin eventually turns green. I wonder if they then release green ink?
What is the biological function of the ink? We all know about squid, which release a dense cloud of ink (black in that case) into which they quickly vanish when danger threatens. But sea hares, despite their name, are sluggish. Their ink cloud is sparse to begin with, and when it disperses, the sea hare is still there.
It turns out, however, that the ink, together with other secretions that are released at the same time, provides a chemical, rather than a visual, defense. A 2005 paper by Kicklighter et al. analyzed the chemical composition of the secretions and their effect on attacking predators such as spiny lobsters. The secretions contain a complex mix of chemicals that elicit multiple, conflicting behaviors in the lobster. Indeed, while some of the chemicals are aversive, as one might expect, others actually stimulate lobster feeding behavior and mimic a food source. The result is that the lobster is not just coated with sticky goo and repelled, but, if it persists, it is diverted to attack a phantom food stimulus—the inky cloud—while the real food item slips, slowly, away:
.
In multiple such sea hare–lobster pairings, Kicklighter et al. found that, if the sea hare was allowed to release its defensive secretions, it escaped from the lobster 60% of the time. But if it had had its secretory glands removed, it escaped only 19% of the time—most of the time, without its chemical defenses, it was eaten.
Reference:
Kicklighter CE, Shabani S, Johnson PM, Derby CD. Sea hares use novel antipredatory chemical defenses. Current Biology 15:549-554, 2005.
Vladimir Brezina (RIP) 
Johna Till Johnson
Wind Against Current 
wow, that is fascinating, thanks vlad … and i love the top photo as well as the video!
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Not my photo, unfortunately—I stole it from Wikipedia. Although we see Aplysia ink in the lab, it takes some preparation to set up a nice photo like that, and I just haven’t got round to it…
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I’m sure you win the prize for the most unusual presentation of the color purple. And to think that I just put a purple clematis on my blog – how lame compared to yours :)
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Don’t sell your flowers short! You can take the most beautiful photo of the most ordinary things…
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This is truly interesting! I’m educated, Thank you so much!
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Entertainment and education, the best of both worlds ;-)
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Gorgeous purple and very interesting post. Wow.
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:-)
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Amazing. Thank you.
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Glad you liked it!
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So incredibly interesting and the photo is amazing!! :D
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Thank you so much! :-)
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Amazing – there’s just so much in nature we aren’t aware of!
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… but we are working to become aware of it!
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Interesting post !!
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Thank you!
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:)
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Great post! So interesting…I would have guessed they use ink like the squid. Thanks for the education!
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It could be, conversely, that squid actually use their ink like the sea hares do—squid ink, too, may have chemical defensive properties. Chances are that nobody has looked at that with squid…
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fascinating. great post, thanks for sharing. :)
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You are most welcome!
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I learned so much here. Perfect rendition of the theme
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It really is the most beautiful, intense purple color… I can definitely understand why Tyrian purple was so valued!
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Love it!
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Good! Thank you!
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Oh wow, that’s so cool.
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I think so too…
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ooo!!!, purple science, i love it, MJ
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Thanks, MJ!
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Fascinating …. nature’s psychedelic lure. A wonderful post, and i learned a new word – phagomimicry.
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You never know when that word might come in handy… ;-)
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Wonderful video and photo for the theme. I never heard of sea hares before.
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They come from Southern California. Once upon a time I worked at UCLA and we used to go with a bucket to collect them from the rocky tide pools around Palos Verdes. The funny thing was, there were hundreds of people poking around these tide pools, including some people who said proudly “I’ve been coming to this spot for thirty years!”, and none of them were aware of the sea slugs, which were all around… The reaction was often “Ewww…” or “What’s that?!?” when we showed them the slugs in our bucket. The truth is, the slugs with their mottled reddish skin are so well camouflaged in the seaweed that it takes some training to spot them. Often the first sign of their presence is a reddish cloud spreading in your footsteps where you’ve trodden on one…
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This is quite interesting. What other colors do you have up your sleeve for us?
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You’ll see when the next color Challenge comes along… ;-)
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Pingback: Weekly photo challenege: “Purple” (The colour purple – A story ) « Just another wake-up call
Pingback: Weekly photo challenege: “Purple” (The colour purple – A story ) « Just another wake-up call
How fascinating, Vladimir – also this from the link you provided to Tyrian Purple – “Recent research in Organic electronics has shown that Tyrian Purple is an ambipolar organic semiconductor” – mind-boggling
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I think that’s a prime example of Wikipedia eccentricity there…
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Very interesting!!!
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Thank you!!
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Your post is so interesting.
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Thank you, Connie!
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Great entry, Vlad!
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Thanks, Cathy!
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What an amazing shot… enjoyed the write up on Tyrian purple too. ;-)
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You never know when information like that might come in handy… ;-)
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Reblogged this on Open Science's Blog.
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Thanks for reblogging!
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WOW! Thanks for sharing this very informative post, Vladimir! It’s very interesting! :)
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Thanks! :-)
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Excellent post! very informative and highly educational. I absolutely enjoyed reading it.
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Educational is always good…
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So nice to learn something..clearly many others feel the same way! Bravo!
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Thank you!! :-)
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It reminds me of the goals of testing BZ (“Buzz”) and other chemical warfare substances on US soldiers during the Vietnam War.
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An unfortunate association… what were the effects in that case?
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Unfortunate indeed. BZ was it’s NATO Pact code name. It was actually called QNB (short for 3-Quinuclidinyl benzilate). It’s creation is supposed to have started in the late 50’s but it was tested un US troops and unwitting civilians as a potential incapacitating agent like that of the slug.
A former US Army psychiatrist who seems to have been was part of the trials published a book on it. It is believed that most infor about the experiments is still classified but what has been released is a long list of signs and sympotoms like:
Restlessness
Dizziness or giddiness
Confusion
Erratic behavior
Stumbling or staggering
Drymouth (cottonmouth)
Excessively accelerated heart rate while subjects are at rest
Fever
Blurred vision
Hallucinations
Coma
Paranoia
Increased blood pressure
Stomach cramps
Vomiting
Euphoria,
Muscle tremor
Frustration
and more swinging from one effect to its polar opposite and back again. It was most unpleasant to say the least.
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Ah, QNB. It’s actually used fairly routinely in neuroscience, as a specific cholinergic antagonist, so I am somewhat familiar with it, although not with its overall medical effects.
Lots of plants and animals have these chemical defenses, which humans have then coopted…
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Wow! We have animals like that in my village! :)
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In Greece? Yes, they are found all round the world. In Greece, it wouldn’t be quite the same species, but a very similar one.
So you can try the experiments for yourself… ;-)
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Another interesting finding about the sea hare purple ink Bursatella leachii:
The Bursatella leachii purple fluid has an enzyme system capable of catalyzing the heparin. Heparin-like anticoagulant is known to occur in marine mollusks. Thus, it is not possible for the compound to act as an anticoagulant, since molluscs are devoid of coagulant system as is present in mammals. Several proteins such as protamines and histones can interfere with its anticoagulant activity. The purple fluid showed activity against the heparin like activity, but did not exhibit any haemolytic activity.
In addition, Bursatella leachii purple fluids contain promising anti-HIV protein called “Bursatellanin-P”(60 kDa).
CURRENT SCIENCE, 82, 3, 2002, 264-266.
Mar. Biotechnol. 4, 2002, 447-453.
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Interesting! Thanks for the links to your papers—I’ll take a look!
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Interesting cross pollinations between seashore life and science/medicine, especially when you factor in the horseshoe crab. I wonder why things living on the seashore should be so important? Interesting article and cool video. I don’t know about the technical terms, but the lobster sure looked stoned. I wonder if the lobster would learn to stay away from the sea hare or if it would keep going back for more like my cat did with catnip? That might help narrow down whether or not the effects of the ink cloud were pleasant or unpleasant. Or at least how stupid lobster are.
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Yes, I think the lobster was pretty much knocked out for a while. And they do learn, so this particular lobster probably would think twice before having a go at an Aplysia again… :-)
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Thanks for the follow up! Very interesting!
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