Comments on: A Genetic Gastric Bypass

By: neil

neil — Tue, 27 May 2008 20:51:43 +0000

Interesting stuff. So the platypus was unable to produce the enzyme that was used to digest in the stomach, the stomach becomes useless and redundant, so they eventually evolve to survive without a stomach at all? My question is how do they digest there food properly without a stomach? do they have “psuedostomach” at the start of the small intestine?

By: slang

slang — Sat, 17 May 2008 23:31:09 +0000

*slaps mr. Benson*

It would be interesting to see if any of the stomach functions have been replaced by other (intestinal?) functions. Perhaps someone can earn a phd on that

By: Michael Gray

Michael Gray — Sat, 17 May 2008 16:18:51 +0000

Thanks, Arturo! Another mystery solved.

That’s what I get for skimming the paper…

By: Arturo De Lozanne

Arturo De Lozanne — Sat, 17 May 2008 13:50:42 +0000

The paper is freely available, nicely written and answers some of the questions above.
It seems that stomach reduction occurred in the ancestor of both platypus and equidna.

Michael: The authors found that gastric intrinsic factor is primarily expressed in the pancreas. They also comment that it is also expressed in the pancreas in dogs. Thus, it seems likely that GIF is functional and can work at the pH found in the duodenum.

Eva: They also talk about possible scenarios for the loss of the stomach. One I found interesting is that stomach reduction may have been selected as a defense against parasites, some of which need the acidic pH for infection.

The mechanisms of gene loss are varied, implying that they occurred secondarily to stomach loss. Again, the paper describes several examples clearly and with nice diagrams.

Thanks for another interesting post Karl!

By: Mary

Mary — Fri, 16 May 2008 21:45:17 +0000

This is most curious and a bit startling – how did the platypus community react to news of their loss? In all seriousness – does this development (undevelopment) aid them in any way? I guess they don’t have to stay out of the pool for two hours after eating, my colleague says.

By: TomJoe

TomJoe — Fri, 16 May 2008 20:27:09 +0000

An even closer look revealed that these genes were not absent altogether, just disabled. These are termed pseudogenes.

By: Michael Gray

Michael Gray — Fri, 16 May 2008 17:53:28 +0000

That’s wild.

I wonder how they absorb vitamin B12. In humans, gastric intrinsic factor depends on stomach pH to bind B12 properly (which is why people taking antacids have to watch out for B12 deficiency).

A quick BLAST brings up what looks like a pretty good intrinsic factor homolog in the platypus genome, but I’m not used to sequence-gazing in eukaryotes, so I don’t know if it’s likely to be functional or not. If so, it must work at whatever pH the platypus gut is at. That could be useful…

Very cool result. Thanks for the link!

By: Jason

Jason — Fri, 16 May 2008 14:49:32 +0000

Oh come on now. We all know that loss of information is not evolution. Right guys?

Oh, right.

By: Eva

Eva — Fri, 16 May 2008 02:04:13 +0000

Do they not have a stomach because they’re missing the (functional) genes, or did the genes become irrelevant (and finally mutated to the point of not functioning) because they didn’t have a stomach anyway?
Did all the genes mutate somewhat simultaneously, or was there one that started the whole cascade?

By: David B. Benson

David B. Benson — Fri, 16 May 2008 01:52:41 +0000

Carl — They couldn’t stomach the only foods they had to eat.

By: Left_Wing_Fox

Left_Wing_Fox — Fri, 16 May 2008 01:51:34 +0000

Oh, is that ever neat! Thanks for pointing that one out.

Any idea how common this genetic break is? If they’ve lost something as basic as a stomach, their diet must make that a selectively beneficial (or at the very least neutral). If that’s the case we would likely expect to see that same break in other species with similar diets.

Or is it at all possible that the genetic damage came first resulting in a beneficial dietary shift?