blue Pelophylax near Toulouse

[Pierre-Yves Vaucher]

I have a lot of Rostand and M Physalix I think in the bibliothèque of my father... I will see and say you.
Thanks Sandra for your work.

[Mario Schweiger]

Not one of the papers searched for, but relavant to this topic:
Significance of recessive and dominant mutations in adaptive processes of the genus Rana in the modern biosphere.- PDF-3915 in DB

Mario

[Gabriel Martínez]

Very strange frog! Black eyes are for me a typical sign of devil possesion. Like the Jeroen female toad

[Berislav Horvatic]

The blue coloration is caused by reflection/scattering of light with short wavelengths from guanine platelets in the iridophore layer of the chromatophore unit in the frog's dermis when xantophores are missing.

For those who (like me) find this wording a bit too demanding, here's a nice paper "for pedestrians"
that clarifies the ABC's: http://jcb.rupress.org/content/38/1/67

Joseph T. Bagnara, John D. Taylor, and Mac E. Hadley
THE DERMAL CHROMATOPHORE UNIT

Abstract
Rapid color changes of amphibians are mediated by three types of dermal chromatophores, xanthophores, iridophores, and melanophores, which comprise a morphologically and physiologically distinct structure, the dermal chromatophore unit. Xanthophores, the outermost element, are located immediately below the basal lamella. Iridophores, containing light-reflecting organelles, are found just beneath the xanthophores. Under each iridophore is found a melanophore from which processes extend upward around the iridophore. Finger-like structures project from these processes and occupy fixed spaces between the xanthophores and iridophores. When a frog darkens, melanosomes move upward from the body of the melanophore to fill the fingers which then obscure the overlying iridophore. Rapid blanching is accomplished by the evacuation of melanosomes from these fingers. Pale coloration ranging from tan to green is provided by the overlying xanthophores and iridophores. Details of chromatophore structure are presented, and the nature of the intimate contact between the chromatophore types is discussed.

(There is a nice picture in the paper which makes all that perfectly clear.)

[Sandra Panienka]

Very strange frog! Black eyes are for me a typical sign of devil possesion. Like the Jeroen female toad

Well, in terms of "Supernatural" the frogs would be possessed by demons (this would be similar to the devil but more subordinate), and if you like to give it sort of an x-filish undertone, it would be black oil (extraterrestrial of course).

@Berislav and Mario: Both great papers.

I think I learned how to make blue and green frogs in the past. I wanna make a brown frog now. So, I assume I just add a bit more of the red component when the frog already appears to be green. I need more carotinoids then ... do brown frogs have erythrophores next to the xantophores then ... but how do I get this really nice light brown that some of the R. arvalis have after the breeding season ... Do I change the reflected light from blue to white in the iridophores and reduce the melanin, too? Can R. arvalis actually reduce yellow and red pigments to appear blue during breeding season? I want more papers!

[Berislav Horvatic]

Can R. arvalis actually reduce yellow and red pigments to appear blue during breeding season?

Ah, what a pity, that's just what I wanted to ask YOU, in the hope to finally find out...
In vain have I searched for anything published on the precise physiological mechanism
that makes R. arvalis males blue. I asked prof. Zoran Tadić, who lectures on animal
physiology here in Zagreb, and he also knew nothing, either on this particular mechanism
or whether there is something written about it...

[Sandra Panienka]

I'm sorry Berislav, that I can't provide a satisfactory answer to that question. I've been looking for an answer to the R. arvails question for quite a while now. It doesn't seem that anyone ever had the guts to get skin samples from blue R. arvalis and to give it a try and publish it. I actually discussed the whole thing with a person I do field work for, he's really educated but didn't have an answer to that blue R. arvalis question, either. I think the answer lies within the hormonal control of the chromatophores, and I am quite convinced that the iridophores do reflect the blue light. I just don't know how good R. arvalis is in reducing the yellow and red components. I've seen pics with blue arvalis that still had some yellowish spots on their flanks, which looked kind of interesting. That's why I would really love to see a paper about it.

[Michal Szkudlarek]

It is just a illusion, like blue color of the sky or white color of arctic bear's fur. Blue color among R. arvalis males in mating season is characterized by structural origin. It is said that this color is caused by lymphatic gathering. Curio- after catching blue male, this color disappear, but returns after releasing him to water.

[Sandra Panienka]

Well, the blue color of the sky is caused by scattering of the sunlight by atmospheric atoms and molecules in the atmopshere, so it is not an illusion, there's physics behind that. I assume that polar bear fur just reflects all light and therefore appears to be white.
I read the stuff with the lymphatic fluids, but I doubt it, because I'd assume that R. dalmatina and R. temporaria would look blue, too, as they also seem to be quite chubby in early spring due to fluid enrichment. Unfortunately, I've never handled R. arvalis when blue, but I'd assume that color change during capturing is due to a change in mood.

[Michal Szkudlarek]

Big apologies, mistaken the illusion of color with green in frogs.