Field of Science

Amphibian Skin

ResearchBlogging.orgI decided to take a break from bacteria today and decided it might be fun to just choose something totally random to write about. Taking a daring leap into the unknown I decided not only to try and find out somthing about multicellular creatures, but about those multicellular creatures about which I know the least: amphibians.
The above picture of an axelotl may have had something to do with my decision. Note the similarity to a pokemon that has accidently wandered into Star Wars.

There are three main orders of amphibians; salamanders and newts, toads and frogs, and caecilians; the blind legless ones that live at the bottom of caves. They are cold blooded and, unlike many other multicellulared animals, they don't regard the outside environment as completely seperated from the inner. They can exchange both water and oxygen through their skin, in fact some salamanders exchange all of their oxygen in this way, and thus don't have any gils or lungs at all.

Skin is therefore a very exceptional organ in salamanders, as it is used for fluid balance, respiration and the transport of essential ions, as well as the more traditional uses of protection and sensing. Possibly because of this, it has it's own protection system against infection. Amphibians have both an adaptive and innate immune system, but in addition to this they have granular glands under the dermis layer of the skin that release antimicrobial peptides in response to stress. Peptide release is stimulated by the adrenergic receptors, so any circumstance of shock of pressure results in an extra layer of protective peptides over the skin surface. They are quite potent as well, providing potential protection from bacteria, fungi, protazoa and even viruses.

As cold-blooded creatures have a slower reacting immune system, this quick, automatic and generic response to stressful conditions provides important protection for the skin, which is vital for maintaining internal homeostasis. And as well as peptide-releasng glands, they also have pigment granules under the skin, which give them bright colours and mean they can change between colours depending on environmental conditions or what they want to communicate.
Amphibians have such beautiful colours...why do they always make dinosaurs blotchy khaki!

There is however a downside to using your skin to take things up from the environment. Water isn't the only thing that gets through permeable skin, chemicals dissolved in the water can as well, which can be fatal if the chemical in question is a herbicide such as atrazine or glyphosate. Chemical contamination may be one reason (and there are, no doubt, many others) for the dramatic decline in the number of amphibians over recent years. Apparently conservationists are majorly concerned about this.

And they don't seem to get as much press as endangered mammals either. Which is a pity because that axelotl does look quite sweet. And amphibians are the only living proof we have left to remind us that the dinosaurs could have had bright-coloured polkadots:
Imagine those colours....on a velociraptor!
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Rollins-Smith, L. (2005). Antimicrobial Peptide Defenses in Amphibian Skin Integrative and Comparative Biology, 45 (1), 137-142 DOI: 10.1093/icb/45.1.137

Quaranta A, Bellantuono V, Cassano G, & Lippe C (2009). Why amphibians are more sensitive than mammals to xenobiotics. PloS one, 4 (11) PMID: 19888346

4 comments:

Toby said...

Thank you for another entertaining and informative post.

And a yellow and black velociraptor would be awesome.

Captain Skellett said...

I agree with Toby. Polka dotted dinosaurs FTW!

takluyver said...

Is there potential for using this incredible antimicrobial peptide in medicine? Is much known about how they are effective against such diverse pathogens (and how they overcome the problem of resistant pathogens)?

Sadly, it seems that the chytridiomycosis, the disease now taking its toll on many amphibian species, is resistant.

Lab Rat said...

Pharmaceutical companies have been screening anphibian antimicrobial peptides for new drugs, I'm not sure how successful these have been, given the general failure of screening programs for drugs in general.

As for the mechanisms of action, I honestly don't know. I'll try and look it up at some point, but I'm a bit crazily busy atm.