Sunday, 8 November 2015

The Frog and Parrot, or Dendrobates tinctorius and Amazona spp.

Dendrobates tinctorius - a form from French Guiana
No, not the name of a pub but a note about Dendrobates tinctorius, the Dyeing Poison-dart Frog from the Guianas and northern Brazil. The species was named ‘tinctorius’ by Cuvier in 1797 because of its use by Amerindians to change the colour of feathers of birds they kept, a process known as tapirage in French Guiana.

If you Google the scientific name, you will find links to a number of American zoos (often the purveyors of howlers and multiple but lesser degrees of misinformation) which describe the process as a legend foisted on early Europeans travelling in South America. However, as far as I can see the process seems to have a perfectly respectable provenance. The history of its description and information on where the process had been recorded was provided by Alfred Métraux* in 1928.

Dendrobates tinctorius - a yellow-backed form
The great Alfred Russell Wallace wrote the following in his book, A Narrative of Travels on the Amazon and Rio Negro, which was an account of his journey made from 1848 to 1852 and published in London in 1853:

They were all completely furnished with their feather ornaments, and I now saw for the first time the head-dress, or acangatara, which they value highly.This consists of a coronet of red and yellow feathers disposed in regular rows, and firmly attached to a strong woven or plaited band. The feathers are entirely from the shoulders of the great red macaw, but they are not those that the bird naturally possesses, for these Indians have a curious art by which they change the coIours of the feathers of many birds.They pluck out those they wish to paint, and in the fresh wound inoculate with the milky secretion from the skin of a small frog or toad. When the feathers grow again they are of a brilliant yellow or orange colour, without any mixture of blue or green, as in the natural state of the bird ; and on the new plumage being again plucked out, it is said always to come of the same colour without any fresh operation. The feathers are renewed but slowly, and it requires a great number of them to make a coronet, so we see the reason why the owner esteems it so highly, and only in the greatest necessity will part with it.

Dendrobates tinctorius
Hans Gadow (1855-1928) also described the process in his Cambridge Natural History volume, Amphibia and Reptilia, published in 1901:

It owes its specific name to the peculiar use made by man of the strongly poisonous secretion of the tiny glands of the otherwise smooth skin. Other species are doubtless employed in the same way. The poison is mainly used for “dyeing” the green Amazon-parrots. This is done as follows:—The green and blue feathers on the head and neck, or other parts, according to the fancy of the operator, are plucked out, and these places are rubbed with the poison, often simply with the living frog, certainly not with its blood, as is sometimes asserted. This operation may be repeated when the new, young feathers begin to bud. The result is that these appear yellow instead of green, and since the Brazilians, and to a certain extent the Portuguese, are rather partial to these artificially-produced freaks or “contrafeitos” as they call them, the industry is kept up.

There is doubt over which animals were used to paint the skin of the; Métraux, in his historical survey notes earlier writings on fish being used; there is also reference to other substances.

Dendrobates tinctorius, a form originally described
as D. azureus
However, back to the frog. Dendrobates tinctorius is highly variable, both in coloration and in body posture. Research using mitochondrial DNA and morphological characters firmly places all the different forms in one species, including the famous Blue Poison-dart frog, originally named Dendrobates azureus. The photographs shown here are of different forms of Dendrobates tinctorius that I kept and bred in my office in the 1980s and early 1990s.

Tapirage does raise questions that I have never seen answered. If the process changes the colour of newly-grown feathers to yellow instead of green, what is happening? Green is partly a structural colour in parrots made up of blue-green light selectively reflected by unpigmented ‘spongy cells’ which then passes through a yellow (i.e. blue-absorbing) pigment to leave green. With yellow the only colour showing after tapirage, there must be an absence of, or derangement in the spongy cells responsible for the blue-green, structural, element.

I have not found any reference to the examination of tapiraged feathers in such a manner that would provide the necessary information. Since photographs of ‘feather art’ are shown in articles, I would be surprised if a museum somewhere in the world did not have examples of tapirage.

The second question is what rôle, if any, is played by the skin secretion of Dendrobates tinctorius in tapirage? If important in achieving the colour change, are the toxins, mainly in this species, the pumiliotoxins, derived from the invertebrate eaten by the frogs, the chemical agents responsible?

†Wollenberg K C, Vieth M, Noonan B P, Lötters S. 2006. Polymorphism versus species richness—Systematics of large Dendrobates from the Easter Guiana Shield (Amphibia: Dendrobatidae). Copeia 2003(4), 623-629

*Métraux A M. 1928. Une découverte biologique des Indiens de l’Amérique du Sud : la décoloration artificielle des plumes sur les oiseaux vivants , Journal de la Société des Américanistes 20 , 181-192. doi: 10.3406/jsa.1928.3646

‡Tinbergen J, Wilts B D, Stavenga D G. 2013. Spectral tuning of Amazon parrot feather coloration by psittacofulvin pigments and spongy structure. Journal of Experimental Biology 216, 4358-4364. doi: 10.1242/jeb.091561