The marbled – greywing mystery
Written by Dirk Van den Abeele, translated by Evy Dens
MUTAVI, Research & Advice group
I don’t think that there is one mutation in Agapornis roseicollis that has had so much name changes than marbled.
The first marbled A. roseicollis was most likely born in America. We can deduce this from the original name of the mutant. In the early stages, one spoke of the “American golden cherry”, which was a deformation of the American cherryhead or simply the American yellow or American yellow pastel. When the first marbled appeared in the aqua and turquoise series, names such as silver, silver cherry etc surfaced. Overall there was enough variation.
While in Belgium the name American golden cherry was customary for this mutation, in the Netherlands the name ‘pastelgezoomd’ was quite quickly introduced. The Dutch name for this mutation was based on his bleached ‘pastel’ body color and the edges on the coverts. This name covered the overall color, but at that time it didn’t take into account that the name pastel already existed for a mutation located on the a-locus (pastel mutant in Agapornis personatus and Agapornis fischeri) and this could cause confusion.
When they started in early 2000 with the composition of the international terms, one has used in the (wrong) English translation of this Dutch name with the approved term: edged dilute. It was a wrong translation because instead of edged pastel they used edged dilute. This is because at that time ‘dilute’ was misused in many countries for what we now know as pastel. Hence probably this mistranslation.
Anyway, we have to admit that the use of both the name ‘edged dilute’ or ‘pastelgezoomd’ (edged pastel)’ can cause a lot of confusion. Dilute and edged are indeed totally different mutations and one can thus confuse this term with a mutation combination of edged and dilute. Despite our attempts to resolve this name confusion, most authorities did not respond. Fortunately this name was used with A. roseicollis without many problems. But when it became clear that this autosomal recessive mutation can also be found in Bourke’s parakeets [Neophema bourkii], cockatiels [Nymphicus hollandicus], parrotlets [Forpus], rosellas [Platycercus eximius], and possible also in a few other species, there was more reaction. Here the use of the term ‘edged dilute’ was not so obvious and caused necessary confusion regarding the name.
Therefore, the term ‘edged dilute’ was discussed in recent years on an international level with different organizations and breeders. Everybody had to admit that the name ‘edged dilute’ may cause a lot of confusion and a solution needed to be found. Until 2009 I tried through different ways to find a proper solution for this matter. There were several options issued by us, but there was no term which everyone was happy with. There was plenty of discussion, but no real solution. There was always someone who had problems with one or another solution but no one came back with a more suitable solution. Finally I put the ball in the other camp and asked the breeders of Neophema species to provide a solution themselves. As long as we had no conclusive international solution, we continued using the international term ‘edged dilute’ and in the Dutch translation ‘pastelgezoomd’ in lovebirds.
In June 2010 this all became accelerated. One morning I got a phone call from Australia with the question if I could provide a solution, because since we asked them to find a solution themselves the discussion was at a standstill. A
Then I called Terry Martin in Australia. Terry is one of the people who, as a vet and bird lover, has been working for years on an international nomenclature. Suddenly everything moved up a gear and it was then decided to use ‘marbled’ as the international term for this mutation. Marbled means literally marbled and refers to the patchy pattern in marble. This term was already used in scientific literature to describe a similar mutation in quails [Coturnix coturnix] which is why this was also suggested in 2009 by Pedro Prieto from Venezuela. Terry Martin discovered by accident that this term was also introduced by Dr. D’Angiera from Brazilië in the 1980s for this mutation. So marbled proved to be an acceptable and supportable solution. As genetic symbol “mb” was chosen.
Since we had with the Dutch term ‘pastelgezoomd’ giving the same problem as edged dilute (again, pastel and edged are separate and different mutations) we also switched here immediately to the international term marbled.
The marbled mutation
Marbled is an autosomal recessive eumelanin mutation which until now is only found in Agapornis roseicollis. In this mutation the bird gets the typical ‘edging’ on the coverts.
The edging occurs because in the coverts the eumelanin reductions concentrates mainly in the core. In an ideal standard bird the eumelanin in the core of the feather is reduced by about sixty percent. That gives light green coverts with a pale yellow inside (core). Because the outer edge of the feather contains more eumelanin this edge is darker. This creates that edged effect in the feathers. The same happens in the primaries. The reduction of eumelanin in the rest of the plumage is evenly distributed, about fifty percent, and is proportional to a pastel bird. Therefore, the edging is only on the coverts and primaries. The rump of this bird is also bleached. Legs and nails are light gray.
So far the standard requirements.
The problem is that not every marbled has the same amount of eumelanin reduction in the feathers. With some, the edged pattern clearly visible, while others have just a limited reduction which makes the overall image paler. This is one of the reasons why these birds or not as popular with the breeders that only breed for shows and exhibitions.
We also see that there are still a few other differences. For example, some marble birds have obvious dark red eyes at birth, while others seem to have black eyes. In other words, there is a lot of variation in the phenotype of this mutation. This leads people to often suggest that there might be different marbled alleles active. In Brazil for example they breed for already a few decades A. roseicollis which are indicated as greywing or “ grijsvleugel” in Dutch. These phenotypes were first imported from America and according to some enthusiasts they distinguish themselves from the original marbled by a clear grey seam on the wings. Others are talking about more uniform and lighter colored birds who they categorize as “greywing”.
So these ‘greywings’ are not new and test mating’s have confirmed that this is the normal variant of the marbled or an allele of marbled, because with combination of these ‘greywings’ with a normal marbled they get different intermediate forms in the offspring.
In theory it would be perfectly possible that the ‘greywing’ really exist, because we have indeed a number of different forms, but I myself do not think that this is the case.
We need to realize that, how much we would like to, we cannot place nature in strictly distinguishable boxes. Certain mutants happen to have a natural variation in their phenotype. We can see this in for example pied birds, but also in dominant edged birds. With this dominant inheriting equivalent of the marbled, we also have birds with a clear edge pattern, while there are birds that have virtually no reduction of the eumelanin. One cannot forget that Mother Nature with this loss of function mutation (loss of eumelanin) will try to make as much as eumelanin as possible. This eumelanin is after all a necessary protection. This can make for quite some phenotypes.
Another argument is that it is a public secret that the best signed and accentuated marbles are mostly males which are also split for SL ino. This might also indicate polygeny of the marble gene?
A last, but not least argument why I think that there is just one allele, is the fact that in every species where the mutation occurs, we see in the first generations these different variations already. Let us take the example of the marbled mutant with Forpus, where we have also several reduction levels and the phenotype is sometimes indicated as edged dilute, pastel or dilute. So the odds are very small, if nonexistent, that in every species, immediately all existing alleles of that locus were mutated. So I think that’s why we should follow the idea that marbled is a mutation with a lot of natural variation and abandon the idea of separate alleles.
Obviously, I can be wrong and I fear that we will only be sure when we can research it at a DNA level. For now this is just a dream. But for all the previous reasons, I prefer to keep it as a very variable mutant and not different alleles. And maybe just to add, if time proves that there is in fact two different alleles (which I doubt), then we need to replace the name greywing. The term greywing is already used for an allele of the dilute locus, a mutation which occurs in budgerigars. But as already said, for the time being, but there are lots of indications that greywing as a separate mutation does not exist.
Dirk Van den Abeele
MUTAVI, Research & Advice Group