Purty Molluscs

[um...]

To make a short story long...

I got my hair cut today, which is something I loathe even more than having my teeth cleaned. (While the results are wonderful in both cases, there's just something awfully disturbing about trying to sit still while sharp/pointy objects are being applied to bits of my head.) As I was waiting for my turn in the chair, I was trying to think of interesting things not to talk to the hairdresser about. (Where did all the barbers go?) While I was staring vacantly at a picture of some lovely model with some lovely haircut vacantly staring back at me, I hit upon chromatophores as a suitable topic to concentrate on while I was being tormented for the next 20 minutes. It was the model's makeup. It occurred to me that chromatophores would be an absolute godsend to most of the women I know. Think of the time, money, and frustration (mostly incurred by male companions) that could have been saved, if only the vagaries of evolutionary pressure had so allowed. (BTW, what's the deal with eyeshadow? ) So here's what's been bothering me:

How did cephalopod chromatophores evolve? Are there any good theories or studies that indicate how this might have happened?

I'm having a hard time convincing myself of a plausible way around that "irreducible complexity" bunk.

 

[um...]

I think I'll use this topic to bookmark some pages I find interesting. This is an article on ceph chromatophore systems by Andrew Packard:

Not for giant axons only

This page links to the following, which has some kinda nifty little movies:

Andrew's Squid Experiments from a Physical Point of View

Here's a story that almost makes me not regret majoring in applied math:

Mathematics reveals the cuttlefish's wink

Wish I had a bunch ('cuddle'? ) of S. officinalis to play with.

 

[Jean]

Think of the time, money, and frustration (mostly incurred by male companions) that could have been saved, if only the vagaries of evolutionary pressure had so allowed. (BTW, what's the deal with eyeshadow? )

I actually think it was a con job by the male of the species! If you look at most other species it's the MALE who gets all gussied up to attract a mate, somewhere along the line we got conned into putting that gunk on our skin for you fellas to admire(?)

BTW yes I DO have some eyeshadow & if you give me a year or so I may even remember where I put it...........don't wear it much (ever!) course that may be why I'm footloose & fancy free at the moment, that and the fact I have no life (the thesis thingy!) and often smell of eau d' squid!

J

 

[um...]

I actually think it was a con job by the male of the species! If you look at most other species it's the MALE who gets all gussied up to attract a mate, somewhere along the line we got conned into putting that gunk on our skin for you fellas to admire(?)

Such is the price of enforcing monogamy (which I happen to prefer, since the alternative seems like too much damned work ). Shall I launch into my rant about De Beers? :x


Mmmmm, eau d'squid...

 

[Jean]

Shall I launch into my rant about De Beers?
:x

If you like, personally, I prefer saphires!


J

 

[um...]

Shall I launch into my rant about De Beers? :x

If you like, personally, I prefer saphires!

Shall I launch into my rant about saphires?

 

[Jean]

Shall I launch into my rant about saphires?

Sure, but I'll ignore you!!!!! (Anyhow I buy my own saphires! )

J

 

[um...]

Shall I launch into my rant about De Beers? :x

If you like, personally, I prefer saphires!

All this talk of sparkly things reminds me of something...

I think my question should be expanded to encompass the evolution of cephalopod body patterning from a holistic point of view. (Does anyone even care? I'm going to turn this thread into a blog, eventually.) Doesn't the efficacy of chromatophores in crypsis/communication depend on the distribution of reflecting cells, iridophores, and leucophores? Does it make sense to inquire about the evolution of chromatophores in isolation?

I'm assuming that the whole papillation(?) issue can be studied separately from colouration. Does that make sense?

Enough questions. I'm going to ... :sleeping: now.

Avast! There be new smilies in the hold: I'll be raisin' a cup 'o me finest grog ta salute the beauties (sorry, Phil) that painted these! Arrrrr!

 

[um...]

BTW; thanks, Jean, for being the only person to reply to this thread. As for you hundred (or so) others...

:P

 

[tonmo]

Well I think these are good questions... in fact I promoted them in the newsletter last week!

Tough ones though... evolution of chromatophores... Have you seen this one?

Shells are often seen as a major contribution to the success of molluscs. Why, then, have many molluscs lost or reduced their shells?

Talks about how the shedding of shells led to the evolution of chromatophores.

That's from Andrew Gray, not to be confused with Andrew Packard from one of your excellent links up there...

Does it make sense to inquire about the evolution of chromatophores in isolation?

I would think so!

 

[um...]

Great link, Tony! That subject could use its own thread...

Loss of the shell, not to mention coevolution with fish, is clearly going to be important in the evolution of body patterning. So we're looking at something like 350 million years (Phil?) of evolution, which is a heck of a lot of generations for animals with such short lifespans. Plenty of opportunity for all sorts of crazy adaptations. Hmmm....

What I've been looking for, most recently, is some kind of investigation into how chromatophores develop in embryonic cephalopods (feeling out the "Evo-devo" angle). Such information is proving very hard for me to find. Any marine biologists out there care to suggest a better method of searching than Google?

 

[Jean]

Interesting the comment that deep sea cephs could get there because they had no shell, Packard (1972) went with the opposite, because the cephs went deep they lost their shells due to increased hydrostatic pressure and then some of the shell-less beasties recolonised the shallow water! I think this is one of those chicken & egg questions! Another one is did the chromatophores develop before the good eyesight or did the eyesight develop because the cephs needed to be able to see the patterns in their school mates It's interesting that Nautilus with relatively poor eyesight has no chromatophores!

J


Reference: Packard, A. 1972 Cephalopods and fish: The limits of convergence Biological Reviews vol 47, p. 241-307

 

[Steve O'Shea]

.... well, they haven't exactly 'lost' their shell, it's just been internalised in most cephs.

Cirrate (finned) octopods still retain a shell (internalised, variably U-, V-, W- or saddle-shaped); Vampyroteuthis has that bizarre shield-shaped vestige; squid still retain the gladius in most (although things like Sepioloidea completely lack a gladius/pen/shell); many benthic octopodids (Octopus and kin) still retain a shell vestige, in the form of dorsal stylets embedded in musculature inside the mantle, in some the stylets are calcareous; Spirula still has a calcareous shell .... and of course there's Nautilus. In non-nautiloids, as a rule the shell has been reduced and internalised, with secondary development in the likes of Argonauta.

... but evolution of chromatophores ..... hmmmm.

 

[um...]

Interesting the comment that deep sea cephs could get there because they had no shell, Packard (1972) went with the opposite, because the cephs went deep they lost their shells due to increased hydrostatic pressure and then some of the shell-less beasties recolonised the shallow water! I think this is one of those chicken & egg questions!

I'm sure I don't really know what I'm talking about, but Packard's scenario seems less likely to me. Perhaps I'll change my mind when I actually read what he has to say.

Another one is did the chromatophores develop before the good eyesight or did the eyesight develop because the cephs needed to be able to see the patterns in their school mates It's interesting that Nautilus with relatively poor eyesight has no chromatophores!

Interesting. Narrow-minded fella that I am, I had assumed body patterning evolved primarily for the purpose of crypsis, with communication being an exaptive(?) development. Now I'm thinking that it might make a lot more sense if it were the other way 'round. It seems to me that crypsis would require a much more complete system to be effective, whereas even primitive stages in the evolution of body patterning could be useful for display/communication.

 

[Bald Evil]

I was wondering if there are any known cephalopods with chromatophores that emit light frequencies outside the visual spectrum. It may be fanciful, but the notion of deep sea cephalopods using short wavelength light emitted from chromatophores as a type of active or passive lidar is appealing to me. I suppose the biggest problem would be the difficulties light has in traveling through water, but if a cephalopod's eyes were adapted to compensate for the diffusion and refraction of deep water, it would make for a very effective detection system. I guess I'm supposing that some cephalopods could evolve (or could have evolved) to use their eyes and chromatophores the way bats use their ears and echolocating sonar. Nature has come up with stranger ideas!

I know this isn't really about how chromatophores evolved, but the 'why' of evolution often answers the question of 'how'.