Cold Adaption

Well, at least they’re not “baffled”: Octopus Cold Adaptation Surprises Scientists.

That's what Octopus vulgaris looks like, if you didn't know

How so? It seems that octopuses (or however you’re supposed to pluralise it) do not adapt for the cold – when it comes to nerve signal transmission, that is – via genetic modification as you might guess. Instead, the actions of an enzyme modifies the transcribed code to produce slightly different proteins: these modifications compensate for the effects of the changed environment on how the protein operates. Not expected, then, but not unimaginable.

But that wont stop Brian Thomas:

Two biologists from Puerto Rico who studied the cephalopods hypothesized “on the basis of conventional natural selection” that the proteins involved in transmitting nerve impulses evolved because the cold water “selected” individual octopuses with cold-adapted mutations. But the research pair, publishing in Science, did not find the anticipated mutations in the animals’ genes.

Something like that, anyway. So, their hypothesis was wrong: you don’t need natural selection here, at least not directly. For those interested, the study abstract is here, and the ScienceNews article is here.

The scientists compared the genes of an Antarctic octopus with those of a warm-water species. Study co-author Joshua Rosenthal told Science News, “It was a real disappointment at first….We thought there was going to be a difference in their genes, but they were basically identical. It was puzzling.”

Of course, given that the the two species – the common octopus, Octopus vulgaris, and another octopus of the genus Pareledone – are not overly related, being from different subfamilies, there will be other differences in their genes. It’s just that in the specific case of the gene responsible for the protein we’re looking at, there are only four.

However, the researchers went on to discover that an enzyme in octopus nerve cells alters the RNA transcript of a critical gene. The gene is transcribed, but before engaging the cellular protein production facilities, a special enzyme edits the transcript by changing specific chemicals. The resulting protein, which forms a channel through which potassium ions travel to reset the neuron after each impulse, performs its action at the perfect temperature-adjusted speed.

From my (rather limited) experience, “perfect temperature-adjusted” is probably oxymoronic. But generally speaking Mr Thomas seems to be correct thus far. Skipping ahead:

[T]he specific edits change just those points along the protein that affect speed, thereby adjusting the speed of the whole neuron. Without this or some similar adjustment, “Antarctic [protein] channels would open about 14 times slower and close about 60 times slower than would tropical channels.”

But could the octopuses even survive in cold waters if they had to move their tentacles 60 times slower?

According to standard notions of how species change and adapt, natural selection should have somehow fixed the precisely appropriate mutations into the cold-adapted octopus population. This would have taken eons and would have required more eons in order to change it back to a warm-water version.

‘Aeons’ seems to have gotten rather devalued lately. In geology, “eons” are about half a billion years: I don’t think that’s a dependable claim for Mr Thomas to make. What he’s alluding to, with his obscure “would have required more eons in order to change it back” comment, is a mention in the news article of how difficult it was for evolution to go backwards, whatever ‘backwards’ is supposed to mean in the context of evolution. Certainly, organisms that used this mechanism of temperature adaptation would have an advantage in a rapidly and repeatedly changing environment.

But with RNA editing, the octopuses can rapidly diversify and fill watery environments of various temperatures. University of Rochester molecular biologist Yi-Tao Yu, who was not involved in the study, told Science News, “If you just modify the mRNA it’s very economical and convenient.”

Curiously, the article went on to say:

Rosenthal and Garrett also examined another polar species from the frosty northern waters off Svalbard, Norway, another tropical species and some in-between species. The researchers found evidence that the same kind of RNA editing happens in those octopuses as well.

The various species that the researchers examined come from very different branches on the octopus family tree, says cephalopod expert Louise Allcock of the National University of Ireland, Galway. This suggests that the RNA-editing trick, or the ability to turn it on when needed, evolved multiple times.

This suggests to me that I’m missing something (not being able to read past the abstract, and probably not being able to decipher the paper anyway). How much do they know about this ‘trick’? Can they say that, or could it be common to all octopuses? Mr Thomas doesn’t seem to be interested:

Leave it to the Creator to have equipped His marine creatures with the appropriate biological mechanisms to enable them to instantly obey His mandate: “Be fruitful, and multiply, and fill the waters in the seas.” The Lord deserves credit for this “very economical and convenient” octopus attribute, which follows from a benevolent and forward-thinking Creator.

Yeah, yeah. Bible reference is Genesis 1:22 if you’re wondering. Interestingly, while this could potentially be used to support the ‘change in behaviour, and not genetics’ idea of the previous article, Brian instead goes the “foward-thinking” route. Another little oddity…


9 thoughts on “Cold Adaption

  1. “Others have shown that the RNA structures that drive editing evolve and generate species-specific patterns, suggesting a plausible mechanism for adaptation”

    From the study.

  2. “Not expected, then, but not unimaginable.” Evolution can not expect, but it is imaginable, that that is designed.


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