At first, I was a bit disappointed in this result, but then I realized it's actually rather interesting in a negative sense. Investigators tested the effects of squid ink on other squid; the entirely reasonable idea being that it could contain an alarm pheromone that would have the function of alerting neighboring squid in the school of trouble. It works — adding ink to a tank of Caribbean reef squid sends them scurrying away.
However, when they removed the pigments from the ink and added that, the squid couldn't care less. That says there is no chemical signal, only a visual signal.
That makes sense, I suppose — oceans are big and would dilute any chemical signal fairly rapidly, so pheromones would only work well over a fairly short range (although some fish certainly do have extremely sensitive olfactory senses, so it could be done). Still, Aplysia eject some potent chemical signals with their secretions, which work when directly squirted into the face of a predator, so there was a chance the cephalopods might have evolved something similar.
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Is all squid ink the same across species? Is it possible that certain inks may have chemical warnings?
But what about cigars?
Synthetic, non-melanin ink, to see whether it triggers the same response?
Test squid ink in total darkness - even if it's something specific to the squid ink, it's not necessarily visually mediated?
Either that, or the pigment is the chemical signal. Did they do a control using a different pigment?
En parte es razonable, cualquier feromona se diluye rápidamente en el océano, en cambio una ráfaga de tinta negra es una buena alarma visual siempre que la profundidad no sea muy elevada y todavía llegue la luz. Los cefalópodos, si no me equivoco, la utilizan para huir cuando se sienten atacados, la Aplysia necesita algo más que un chorro de tinta para aullentar a sus agresores.
I didn't know Aplysia had a secretory defense. We had to remove their respiratory ganglion in my neuroscience lab a few weeks ago. I thought the unfortunate smell was simply the mixture of dead snail and disinfectant, but if there is also a chemical squirt of unpleasantness mixed in, that would help explain things...
It makes sense that squid would use visual rather than olfactory alarm signals since they're very visual creatures, judging by the size of their eyes and the fact that their fellow coleoids octopi and cuttlefish use visual signals on their skin to communicate.
Neat. Of course, if someone threw a bucket of piss in my face, I think I'd be pretty alarmed too.
Well, squid are diverse and many, right? I'm not sure I would want to extrapolate a result from one species to all without some further checking. (Or do we already now that most squid ink is the same, with only a few notable exceptions, as you note.)
s1do @#5 : Translated via hyperwords
Squid might not respond to any pheromones in the water, but do their predators?
Plus squid being active animals, any predator is generally going to have to be pretty fast to catch one. Visual cues travel faster than olfactory ones, and by the time the pheromone triggers the escape reflex it might be too late. IIRC some squid have bioluminescent ink, so that solves the problem when living at depth.
It would be interesting to see what response other Aplysia have to their "inking" signal. Does it trigger an escape response?
Not sure I agree with you here:
That says there is no chemical signal, only a visual signal.
That makes sense, I suppose -- oceans are big and would dilute any chemical signal fairly rapidly,
For one, many species can detect chemical cues over astonishing distances in the ocean, sharks famously for example. For another, roughyl half the hours of the day, and all the time below a certain depth the visibility is severely limited due to a lack of sunlight.
Add to that conditions that can reduce visibility to near nothing, and you have a signal that often goes undetected by eyesight alone.
Sound is really the best alarm signal u/w, perhaps there is also a sound, such as beak clicking or a specific type of muscle contraction that makes a sound that squid and detect that goes along with the inking, and the visual cue is only one small part.
On the other hand, as cool as they are, squids are mostly food for others, so perhaps being slaughtered by the dozens is part of the overall {cough} plan...
@ Dave Godfrey
IIRC some squid have bioluminescent ink, so that solves the problem when living at depth.
Interesting, but that still doesn't help much when visibility is limited by silt or just a massive school. If inking also serves as a warning, I think there must be more to the story than just what is looks like.
Come now, you could as easily say "The atmosphere is big and would dilute any chemical signal fairly rapidly", but we both know scent signals are not uncommon in terrestrial animals. Using a liquid diluant instead of a gas doesn't change that. Also, it seems that squid ink has a gloppy, mucos-like consistency that prevents diffusion in water, which would also tend to retard diffusion of any associated chemical signals.
The adjacent aquarium experiments were nice--there definitely seems to be a visual component, but I'm not convinced that's all there is. I'd like to see the experiment performed on a species of squid that did not typically live in well-lit environments. Also, the melanin was removed by centrifugation, which would also remove any chemical signal associated with a high sedimentation coefficient component--I'd like to see what would happen if they just bleached out the melanin with potassium permangenate.
I see that at least #1, #3 and #4 have made the point that I wanted to make - viz. that (on the bare account you've given) the researchers don't appear to have checked whether (at least one of the ingredients of) the ink doubles up as a chemical signal. They would need to try a similar colour ink (and then different colours) made of completely different ingredients. One thing we know for certain about the way evolution works is by re-using one thing as another thing until optimisations of their specialised uses diverge.
Drew,
That's not terribly useful for exploiting an alarm pheromone, however. "There's a predator somewhere in these five cubic miles of ocean, or at least there was within the last four hours! Be afraid!" Even if squid could sense the concentration gradient and thus get a bearing on the attack location, it would tell them little about the present danger; their predators are too numerous and too fast.
Reef squid shoals get attacked roughly seven times a day by predatory fish, according to one source, and their primary defense is sprinting away en masse. They need an instant signal that can be well-localized in space and tine.
Reef squid live in shallow and very clear water, though. And they're visual predators who hunt largely after dark, so evidently visibility isn't too bad for them at night.
Depends on the terrain. In open water, sound's ability to go around obstacles may not be that valuable, and it's also harder to localize than a visual signal. Also, squid seem to have fairly rudimentary hearing but really excellent eyesight, and their inking behavior is already selected for maximum visual effect.
There's a predator somewhere in these five cubic miles of ocean, or at least there was within the last four hours! Be afraid!"
not at all. think about alarm signals in mammals that use sound.
there are indeed "general" alarm sounds of just that type:
"predator in general vicinity, keep a lookout".
that said, IIRC, inking is primarily used in response to direct attack (at least this is so in octopus, I have not looked at squid directly), so it seems to me it would be less likely that it would also serve as a "general warning".
if squid ink at the slightest hint of danger (which would be news to me), then the idea of a general warning is plausible.
Moreover, have they looked at inking under different circumstances? there could be different signals (visual and chemical) under different threats. Again, this would be comparable to other animals that have specific auditory signals for different predators, etc.
Reef squid live in shallow and very clear water, though
if they live in the tropics, that's mostly correct. Not so in temperate waters. Especially in upwelling areas where they often congregate to feed.
visibility can often be limited to less than 10 feet (from personal experience diving temperate reefs for about 25 years).
which makes me wonder, of course, if there would be observable differences in inking behavior between temperate and tropical squid.
Dammit Capital Dan! Your bucket full of piss comment made me damn near choke to death on my coffee.
Out of my depth here, but doesn't it seem like directionality might play a big role? Smells are not very directional, and so (if I'm not mistaken) aquatic things that need to navigate based on scents actually have to sample some region and pick up a gradient in the smell do determine directionality.
That doesn't work very well for a quick response in fleeing from danger in a particular direction. Vision is a quick response with directionality.
Ichthyic,
But those alarms have very good temporal resolution--even if they don't indicate exactly where the predator is, you know it's around right now. Long-distance chemical cues, not so much.
And actually, squid may already have such an alarm, but in a visual mode--the paling display when threats approach. That's sometimes mirrored throughout a shoal, I believe.
These are Caribbean reef squid; it's very rare for them to move north of Florida's southern tip.
Anton Mates:
My shark example was only to refute the idea that chemicals dilute too fast in the ocean to be of much use.
And even in the Caribbean, a place I have had the pleasure of diving many times, visibility can still be an issue, sometimes dropping to 10 feet. For an alarm indication, sound is the best medium. A visual cue like an ink cloud would only warn those individuals who are close enough to have already seen the predator in the first place.
And what would differentiate an ink cloud from alot of blood? Below 30 feet or so blood would look the same as ink colorwise.
Just a few thoughts.
I lived in Sicily for about a year. And at a restaurant was served pasta with a sauce made with squid ink. It certainly had a distinctive and not altogether pleasant taste. I could easily imagine that taste being noticeable in the water - though to what distance, I don't know.
OK - This is a good time to ask you marine and aquatic biologists about a couple of things I always suspected were myths.
First, the shark thing. I've heard, sometimes on quality programs like Nature, that sharks can smell blood up to several miles away and will sometimes appear on site from those distances after blood is poured into the water. It's always seems to me that ions or suspended particles dispersing in a large body of water would seldom disperse through dilution or Brownian movement at more than a few dozen feet per minute at best.
Second, fresh water fishermen in rivers and ponds swear by "solunar tables" that predict "the bite" as a function of tidal forces (not tidal depth). It seems to me that since a fish controls their bouyancy at almost always very close to neutral that at most the only effect a fish could experience from changing tidal forces would be that they might move up or down in the water column by a few centimeters over a six hour period - that's if they never adjusted their bladders which they have to do continuously anyway as they move around after food, etc. Would they say, "Gee six hours ago I was sitting here 450 cm above that rock. I haven't moved for six hours and now that rock is only 385 cm below me. It must be dinner time."?
So, how fast can any solute disperse through an infinitely large solvent - and, how can a fish in a water column have any ability to sense tidal forces at work on that body of water that it is suspended in?
What say you?
#22: And what would differentiate an ink cloud from alot of blood? Below 30 feet or so blood would look the same as ink colorwise.
Which strikes me as possibly exactly the point. IE, the instinct is to flee blood, and the ink looks/acts the way it does to mimic the appearance of blood, and trigger the fleeing in the same way, but before any squid's actually gotten chomped...
I could be way off, but it's the thought that just struck me.
These are Caribbean reef squid; it's very rare for them to move north of Florida's southern tip.
i was talking different species of schooling squid, like Loligio, for example, that live in temperate waters.
First, the shark thing. I've heard, sometimes on quality programs like Nature, that sharks can smell blood up to several miles away and will sometimes appear on site from those distances after blood is poured into the water. It's always seems to me that ions or suspended particles dispersing in a large body of water would seldom disperse through dilution or Brownian movement at more than a few dozen feet per minute at best.
that would be accurate if there were no currents in the water at all, but that's pretty rare out in the ocean.
In fact, it's differential currents that often allow sharks to track the source of a particular chemical quickly. general dispersion would not enable the sharks to home in nearly as quickly.
btw, most of the accounts of sharks homing in to blood are from boats trying to attract sharks by actually dumping chum/fish blood in the water, and typically they indeed either set up in a current, or actually move the boat while dumping, thus setting up what is known as a "scent channel".
I know, because that's what we used to do to attract sharks for tagging purposes.
Second, fresh water fishermen in rivers and ponds swear by "solunar tables" that predict "the bite" as a function of tidal forces (not tidal depth).
fish often migrate inshore with incoming tides to feed. The mechanism of tidal detection is not relative movement within the water column, but more likely either current shifts or actual detection of shifts in gravity as the moon passes overhead, or even slight differentials in pressure.
it kinda depends on the critter under discussion.
@ Jake #24
#22: And what would differentiate an ink cloud from alot of blood? Below 30 feet or so blood would look the same as ink colorwise.
Which strikes me as possibly exactly the point. IE, the instinct is to flee blood, and the ink looks/acts the way it does to mimic the appearance of blood, and trigger the fleeing in the same way, but before any squid's actually gotten chomped...
Not entirely true. Squids are ravenous predators, and may well be attracted to and excited by the presence of blood in the water.
Personally I think ink is strictly a predator avoidance tactic, and any secondary function like an alarm is coincidental. And to that end anything close enough to see the ink cloud is also close enough to see the predator. Kind of renders the visual alarm moot at that point...
Below 30 feet or so blood would look the same as ink colorwise.
actually, again, that depends on the critter and the exact depth.
cephalopods use hemocyanin instead of hemoglobin, so their blood is not red (it's pretty clear, or very light blue).
while red light filters out of the water column fairly early (yeah, around 30 feet give or take), other colors penetrate much farther (blue/green the farthest).
at 90 feet, red blood actually takes on a chartreuse color.
Personally I think ink is strictly a predator avoidance tactic, and any secondary function like an alarm is coincidental.
ditto. It would certainly be cool to show it being used as a social signal, but I don't think the evidence is strong enough yet to conclude that from this paper.