I have been wondering what genetically causes frogs to lack melanin as well of the roles of chromatophores in their colouration. Its the role of chromatophores and other pigment cells which I am unsure of. What are the specific roles of xanthophores and erythrophores in amphibian colouration?
xanthophores contain mostly yellow pigment. I searched for erythrophores, they are primarily found in fishes which gives red color as name suggests. The next type of pigment cells in amphibians is called iridophores which contain reflective iridescent pigments.
http://www.devbio.biology.gatech.edu/?page_id=530
At the molecular level, genetically induced abnormal coloring in amphibians can easily come about by any mechanism that interrupts the steps necessary to generate a pigment. Essentially, any mutation that interferes with synthesis of the pigment can result in a phenotypic expression lacking that pigment. In the case of leucistic amphibs (pale, lacking melanin) there are six steps involved synthesis of melanin, starting with Tyrosine. A simple point-source mutation affecting any of the enzymes involved in melanin synthesis would be sufficient to produce these pale forms. I witnessed an event in Western Toads in a large pond in which about 1% of the thousands of tadpoles appeared white from a distance. On close inspection, they were shiny beige or pale gold and thus not albino. Interestingly, these pale individuals also failed to metamorphose but stalled at early limb-bud stage. Turns out that thyroxine synthesis and melanin synthesis both start with Tyrosine. Dosing these leucistic tadpoles with a little T-4 resulted in immediate progression towards metamorphosis although none successfully completed metamorphosis.
I have also seen frogs lacking red or yellow coloring, and have been able to demonstrate that this defect is a genetic recessive trait that recurs in a single population of frogs at a fairly constant rate of between 1 and 2% of the population but occurs in about 25% of the offspring of crosses between two normal-colored carrier parents, and in 100% of offspring of a cross between two of mis-colored frogs. .
this may interest you
TATTERSALL, GLENN J. ; ETEROVICK, P. C. ; de Andrade, D. O. V. . Tribute to R. G. Boutilier: Skin colour and body temperature changes in basking Bokermannohyla alvarengai (Bokermann 1956).. Journal of Experimental Biology , v. 209, p. 1185-1196, 2006.
Color in amphibians is relatively strait forward. They have three types of chromatophores. Iridophores are structural chromatophores that reflect light back in the blue spectrum. That light can pass back through xanthophores, which tend to be red, orange, or yellow pigments. When you pass blueish light through a yellowish pigment, you get green...which is why it is a common amphibian color. The third chromatophore is melanin, which can squeeze up between other cells and chromatophores. Melanin is brown/black, so can block the reflectance of blueish light, or obscure xanthophores. Depending on the structures present in different locations on a animal or among species, you can get dramatic color patterns from these three basic chromatophores. Further, any genetic mutation that results in the absence of one type of chromatophore or the overproduction of a chromatophore can can create bizarre looking individuals. We routinely encounter blue Green Frog (Lithobates climatus). These individuals presumably lack xanthophores, so we see reflected blue light rather than green.
Hello, this is a article with general information, it could be interesting for you:
Morrison and J. Hero. 2003. Geographic variation in life-history Characteristics of amphibians: a review. Journal of Animal Ecology 72, 270-279.
Dear Steven
An interesting question, though simple in words but very deep to ponder upon. I am doing study on the very same aspect here in tropical India. For this we have to consider three aspects.
1 Frogs that live on ground tend to be drab , olive, brown or mosaic of these.
2 Frogs in bushes are brightly coloured; green, yellow or shades of brown to reddish tone.
3 Frogs of stream are brown, green or dark shade of these colours.
I have found that colour of frog skin is not a determinant character to conclude a species as frogs tend to change shades, stripes, spots and even dermal ornamentation upto some extent !
At the moment I cannot say in motion of xanthophores or any other pigment but I ve shared my results with you.
Hope, this has some direct or indirect relation.
Thanks.
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