Last week’s Friday Cephalopod actually has an interesting story behind it. It was taken from a paper that describes the evolutionary radiation of deep-sea cephalopods.
First, a little background in geological history. Antarctica is a special case, in which a major shift in its climate occurred in the last 50 million years. If you look at a map, you’ll notice that Antarctica comes very close to the southern tip of South America; 50 million years ago, they were fully connected, and they only separated relatively recently due to continental drift.
When they were connected, South America acted as a barrier to ocean currents, shunting warmer water south to moderate Antarctica’s temperature. The Antarctic waters at that time were a cool but pleasant 20°C. The two continents split apart about 34 million years ago, allowing rings of circumferential currents to surround Antarctica, isolating it from the warmer waters of the north and plunging it into a deep freeze; within a few tens of millions of years, the water temperatures dropped to about -1°C, the current temperature. It had almost certainly reached close to these frigid temperatures about 15 million years ago, when there was a strong expansion of the Antarctic ice sheet and the development of cold, deep currents emanting from the waters around the continent.
This kind of change in the environment imposes new stresses on the organisms living in it; there were also radical changes in the fauna of the Antarctic ocean concurrent with these temperature shifts. Sean Carroll describes these effects in his book, The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution(amzn/b&n/abe/pwll) (which I recommend highly), in which he discusses the evolution of notothenioid fish, the icefishes. These animals survived the gradual cooling by the evolution of antifreeze proteins, modifications to their cytoskeleton that made them more stable in the cold, and reduction of, and in some cases complete loss of, red blood cells to reduce blood viscosity. It’s a very cool story in which geological events are neatly correlated with molecular changes, as Carroll diagrammed below.
Not just teleost fish had to adapt, obviously — the invertebrates of the region faced the same stresses. The current work did not address the physiology of Antarctic cephalopods (I hope someone does, though!), but looked instead at the relationships between Antarctic octopus species and deep sea octopus species. They noticed a similar interesting correlation: the lineages diverged approximately 33 million years ago, and there was a subsequent radiation of new forms into deep ocean waters about 15 million years ago. The cladogram below illustrates the pattern — the cephalopods endemic to the Antarctic are in blue, while deep sea octopuses, which are found far, far north of the Antarctic, are in red. They’re related!
(Click for larger image)
Phylogenetic relationships of Southern Ocean endemic and deep-sea octopuses. Bayesian phylogenetic tree based on the results of the relaxed
phylogenetic analysis utilizing the seven genes: rhodopsin, pax-6, octopine dehydrogenase (ODH), 12S rDNA, 16S rDNA, cytochrome oxidase subunit
I (COI) and cytochrome oxidase subunit III (COIII) of 12 Antarctic octopus species, seven deep-sea octopus species and 15 outgroup taxa. The
topology is that from the posterior sample which has the maximum sum of posterior probabilities on its internal nodes. Each node in the tree is
labelled with its posterior probability, * indicates a posterior probability of 1.0. The divergence times correspond to the mean posterior estimate of
their age in millions of years. The genera Adelieledone (dark blue), Pareledone (blue), and Megaleledone (light blue) are endemic to Antarctic waters.
The deep-sea genera, Graneledone (red), Velodona (yellow), and Thaumeledone (orange) are a monophyletic group and are nested within the Antarctic
clade. The deep-sea clade was estimated to have originated around 33 millions years ago (Ma; 95% HPD interval 5-64 Ma). The three deep-sea
genera were estimated to have diverged from one another around 15 Ma (95% HPD interval 1-36 Ma). Depth ranges were taken from the literature
as follows except for P. turqueti and A. polymorpha (Allcock, unpublished data): A. piatkowski (Allcock et al., 2003a), Pareledone spp. except
P. turqueti (Allcock, 2005), M. setebos (Allcock et al., 2003b), G. antarctica (Voss, 1988; Vecchione et al., 2005), G. verrucosa (Allcock et al.,
2003c), G. boreopaciï¬ca and V. togata (Voss, 1988), T. peninsulae (Allcock et al., 2004; Strugnell et al., 2008), other Thaumeledone spp. (Allcock
et al., 2004).
The map below gives the geographic perspective — these species are dispersed over a large part of the world’s oceans, from an origin in the Antarctic.
Distribution of deep-sea octopus species showing the southern focus of their distribution. Includes all species of Graneledone (red),
Thaumeledone (orange), and Velodona (yellow) according to most recent taxonomic revisions of each group. Blue line is schematic pathway of the
Antarctic Bottom Water ï¬ows of the thermohaline circulation from Rahmstorf, 2006 (18) re-projected using the Lambert Azimuthal Equal Area
projection.
It’s developing into a powerful evolutionary story. Geographic isolation and environmental change lead to adaptation of local species, and the adaptations to these special conditions, cold and darkness, open up new niches in the deep sea for these animals. Their distribution is further abetted by currents that formed 15 million years ago, when cold Antarctic surface waters sank and flowed north in the deep ocean, carrying pre-adapted cephalopods with it.
Strugnell, JM, Rogers AD, Prodo PA, Collins MA, Allcock AL (2008) The thermohaline expressway: the Southern Ocean as a centre of origin for deep-sea octopuses. Cladistics 24:1-8
If such a big environmental change has to occur for drive one instance of cephalopod speciation (I’m not saying that is must), then I wonder if the previous and following speciation events were all allopatric.
I have recently changed my mind about the feasibility of sympatric speciation; now I think that it is perhaps the main mode of speciation. Are the ranges of the deep sea octopuses overlapping at all?
Just wait till they take to the land…
Radiation! Well, I wouldn’t put it past them.
Glen D
http://tinyurl.com/2kxyc7
So how long until the secret base in Lake Vostok from which the ice cephalopod empire is ruling the frigid waters gets found?
‘to’, even. Damn, I’m too vain
forto let that stand.My speciation theory professor just told me that “Sympatric speciation is like the measles. Most people catch it at some point, but they all get over it”.
This research is cool.
Well, actually, I’d imagine it’s freezing!
What would it take for a freshwater cephalopod to evolve? Could we engineer one with genes from freshwater snails?
Whenever I see PZ’s bookstore superscripts (amzn/b&n/abe/pwll) my wallet cries out in anticipatory pain. Good thing I have a nerdy niece who likes getting books for Festivus.
I would have thought the cephalopods have had ample opportunities to invade freshwater habitats, all those large estuaries. I can think of at least two reasons. Firstly due to a difference in nutrient levels there is more biodiversity in the oceans so therefore more food opportunity. Secondly many cephalopods have essentially planktonic young, not good for river living, though not insurmountable. The fish have done this one, salmonids and eels for eg, but cephalopods are not distance migrators which would make it hard for mature animals to move upstream. I do wonder though, not being up with nautiloid fossils whether any of them might have been freshwater adapted.
Great stuff! Keep it coming.
They only radiated out in three directions?
Didn’t anybody tell them about the importance of maintaining fractal consistency?
After all that wading through quackery and denialism recently it’s certainly refreshing to see a post about such a really cool (no pun intended) topic here! Thanks a lot from quack-infested Germany!
If the fish lost their red blood cells, then do they just have hemoglobin circulating in solution in their plasma?
-jcr
No, no hemoglobin either, and not even myoglobin. They survive on just the oxygen dissolved in plasma (it helps a little bit that oxygen dissolves more readily at low temperatures).
Would I be correct in guessing that a no-hemoglobin circulatory system would be substantially less efficient, and limit the size these fish could grow to?
-jcr
Yes, and the temperature is limiting, too. Put these fish in warmer water, and they basically suffocate.
Very interesting. One other thing I’ve wondered about Antarctica is what happened to its terrestrial species. Did they die out suddenly due to the loss of plants that make up the bottom of the food chain, or did they evolve into the seals, penguins, etc. that are there today? Did they escape to South America as Antarctica cooled down?
-jcr
I think I saw a movie once about the irradiation of deep sea octopuses. They grew to monstrous size and started attacking . . .
What’s that?
Oh. Never mind.
Wonderful. An evolutionary explanation that integrates evidence from geology, oceanography, climatology, physiology, genetics and biogeography. Is anyone looking for similar radiations in other taxonomic groups?
I mean specifically radiations with a similar geographical pattern to the octopuses, centred on the Antarctic and going down into deep waters.
Also known as ‘a comfortably warm 20°C’, I think you’ll find.
(Hello Houston, we’ve gone past Mars…)
That movie was on SciFi yesterday afternoon, nestled between all the Z-Grade Killer Croc flicks. That’s not to imply that Octopus 2: Electric Boogaloo was any better than Z-Grade, though…
Thanks for this helpful new angle on cephalopod evolution. For those of us familiar with Carroll’s telling of the icefish stroy, the tie-in between the two and Antarctic geology was a bonus.
I knew it!
Radioactive octopi from Antarctica.
And they all laughed at me;P
This book Pz recommends, “The Making of the Fittest” is great, I read it just recently. A good companion book is “Endless Forms Most Beautiful” by Sean B. Carroll. The two texts dovetail in an interesting and enlightening way.
Did he mention that that had originally been said by Theodosius Dobzhansky?
For unknown reasons, there are no freshwater cephalopods and never have been.
Air of 20 °C is comfortably warm. Water of 20 °C is quite chilly.
No. Glaciers advance way too fast for that. The penguins are much older than the ice cap, and seals are not southern mammals, they are closely related to weasels, badgers, martens, otters and the like and come from the northern hemisphere.
Many must have done so before the landbridge ripped apart, but remember that first the landbridge broke and then western Antarctica froze over…
Wow, that’s cool. Looking at the circumpolar current diagram, I couldn’t help but be reminded of the ring speciation of arctic herring gulls described by Dawkins in The Ancestor’s Tale, and wonder if something similar has been observed in species around Antarctica during the violent speciation induced by the climate shift.
(Yes, I realize this particular example isn’t completely unambiguous, but the concept is so fascinating!)
Continental drift, yeah right, you wouldn’t be trying to placate the religious would you.After all the world was made ? years ago and then decided to drift? apart.Time to shake the dead wood out of geology, this isn’t our fathers world anymore. We are growing up and it’s time academia grew up too.
Damn, it’s been years since I saw one of those those T-shirts.
I was just about to link to Darren Naish’s rant on Tet Zoo…
Dawkins also wrote about salamander ring species around California’s Central Valley, which I have not seen argued against anywhere.
And the next thing they will try to shove down my thought is that sprites elves and halo’s originate in clouds.Come on. If you know anything about electricity and where it comes from,It is a one way path from core to core.You know we are still struggling from a dogmatic religious load of crap and academia is still contributing to this delusion.There is a reason why Samual Warren Carey and Nikola Tesla were censered, it did not fit in with the religion of the day.
Actually, in semiconductor theory class, we found that a model that includes both electrons and holes (the absence of an electron) moving in opposing directions fits the data best. Your mileage may vary.
Now I have an image of priests swinging incense canisters at their heads. Good thing it didn’t stop AC current from becoming the standard.
NPN-PNP, Gotcha I’m not talking about AC/DC power once it reaches earth…I’m talking about the source and the sink.
Assumtions made can be useful, However once more knowledge is gained, Academia is like an old man who would rather shout than use a phone.Very slow to adapt.
They *have* started taking over the land!
http://zapatopi.net/treeoctopus/
Sphere, do you have a real point? At the moment, you are sounding like you are on some hallucinogen. If you have a theory on something you wish to express, please cite the scientific literature instead of making vague remarks.
Sphere, if you want to discuss a theory, a better place would be this thread rather than this antarctic octopus thread.
Sorry for the off topic please continue.
They suffocate in warm water? It doesn’t sound hopeful for them if the waters around Antartica are warming up, then.
Regarding comment #11:
Strictly speaking they only radiated out in one direction: North.
But, then, South Polish jokes aren’t to everyone’s taste so I’ll stop now.
“Strictly speaking they only radiated out in one direction: North.
But, then, South Polish jokes aren’t to everyone’s taste so I’ll stop now. ”
That was a joke lol? A pun yes, but oh well. Iprefer Pum, but that is a referance not a single person will understand, so oh well.
Cool, no red blood cells! That is very intriguing and surprisingly original, unlike most other evolutionary redundancies (for example, the “lenses” in the back of predators’ eyes that increase their visibility. There are even a couple of poisenous birds- cool huh?
I am interested to know if there are any other perticularly bizarre evolutionary developments that have occured without my knowledge.
Well without intimate knowledge of your personal ignorance, it is hard. However, how about the tunicates (sea squirts) they are part plant. Seems they acquired the whole cellulose synthesis pathway from an algae. Their tunic, the leathery bag they sit inside is made of cellulose. Why innovate when you can get off the peg?
And I recently read of a sea squirt that is also part plant, only in this case it has modelling the latest in photosynthesis pathways. They just have to bask now. This is different from the symbiosis in cnidaria like corals, the sea slug has just taken the proteins and thrown the rest of the algae away. if that happened to a terrestrial slug you would have something like Day of the Triffids though.
Yeah – understanding what happened to most of the organisms in Antarctica helped me realize (while I was still religious) that the universe just doesn’t give a damn about life.
Anyway, very interesting.
Pretty much anything about antarctic fauna is gonna be interesting. The icefish, going back to something mentioned earlier, has the narrowest known temperature tolerance range of any known organism. A few degrees either way and it’s about as functional as Ray Comfort in a biology class.
Are these guys in a similar vein in terms of temperature tolerance? Anyone know?
As long as we’re on the subject of interesting adaptations, the parasitoid flies have some really cool examples of convergent evolution. They have these modfied abdominal segments they use to peirce the exoskeleton of their victims to inject their eggs (or larvae). They’ve evolved seperately 5 different times in the various parasitoid lineages. If I remember my reading correctly, the parasitoid flies also evolved from saprobes…apparently living in a toxic decomposing corpse is a pretty good pre-adaptation for living with a toxic immune system.
I’m just impressed by how far South SA actually goes …
“Tunicates (sea squirts)-they are part plant.”- Neat. “Feeeed me Semore!”
One thing i think would be a cool adaption was for some plants to shoot seedlings with fibrous material strung along behind them. In jungle environments, this would produce a lot more area that could be used by the plants to photosynthesize, as they grow along the strands and form sheets. Perhaps it’s just unfeasable for some reason.
more cool stuff:
http://en.wikipedia.org/wiki/Pitohui
http://en.wikipedia.org/wiki/Platypus
http://en.wikipedia.org/wiki/Echidna