an Update to the article:

Different Strokes for Different Birds

The Nature of the Opaline Locus

by Terry Martin BVSc of Brisbane, Australia

Since my original article on the opaline locus, I have been fortunate in being able to collect further information on the Opaline Turquoisine Parrot, as well as some new information about possible new opaline alleles in other species. The following is therefore an update on my current level of understanding for the opaline locus.

In my original article I listed several identification features for opaline alleles. Point 2 was the change of down colour to white. I must now clarify and define this change more precisely (an oversight in my original essay).

Point 2: Melanin is removed from the down feathers, no change is made to the psittacin content of the down.

This is the correct interpretation of what happens. When I first wrote my original article I was only really considering the main species I kept personally, which have only melanin present in the down. But further investigation has made me realise that I initially had overlooked the effect in species with psittacin in the down. Cockatiels have only psittacin in their down, no melanins, therefore this effect of the opaline allele can not be judged in this species. White down is only produced in Cockatiels by mutations that alter psittacin pigments. And I have become aware that some species, such as the Peachface Lovebird, have both psittacin and melanin in their down. In the wildtype it appears as a dark yellow colour. In this case, loss of melanin produces a brighter yellow down. Loss of psittacin produces a grey down colour and loss of both is needed to result in white down.

I also wish to clarify that the underwing stripe in the Australian species is enhanced and become visible on the upper surfaces of the flight feathers as well as the bottom surface and the underwing coverts also carry retained white wing stripes.

In both my original article and this update, I use the term ‘enhancement of psittacin pigments’. I should make it clear what I mean by this terminology. In opaline mutations we see differing changes to the psittacin pigments deposited. In some species greater quantities of psittacin are deposited. In others one psittacin pigment may replace another. I view the process that is occurring in the following way:

“Yellow psittacin is the base psittacin pigment, with oranges, reds and pinks created through metabolic changes to the pigment. They are refined (secondary) psittacins, produced from the base yellow pigment.”

Enhancement therefore may imply increased deposition of base yellow pigment (if this is possible) or increases in secondary psittacin pigments. Secondary psittacin will only be produced and enhanced if it is naturally in the phenotype, in which case it will be enhanced in preference to the base yellow psittacin.

Turquoisine Parrots

I have recently had the opportunity to observe a few Opaline Turquoisine Parrots and I can confirm that they exhibit all the important features for opaline alleles. There is reduced distribution of melanin pigments, with the loss originating in the middle of feathers, leaving a crescent of melanin at the top of the feather. Psittacin pigments are enhanced, with red being selectively increased and spread to new areas of the plumage. The wing stripe is retained and enhanced in both cocks and hens. And the birds have loss of melanin from the down. Most importantly the mutation is inherited in a sex-linked manner.

Opaline alleles in non-Australian species

Approximately four months ago, a discussion group for Psittacine genetics was started on the Internet (see Other Sites index). The topics covered have been broad and numerous in nature, but out of the discussions four possible new opaline alleles in non Australian species of parrots have been identified.

Peachface Lovebird

In the Peachface Lovebird there is a new mutation called Roseheaded in the USA (See Royal Rose Aviaries and associated Article). It exhibits most of the features of opaline alleles in other species. There is reduced distribution of melanin pigments on the back of the head and in the tail. When combined with the partial blue (parblue) alleles, the crescent of retained melanin in feathers is evident. Psittacin pigment is increased in its distribution and enhanced. The rose of the face spreads over the back of the head, red is increased in the tail and yellow is spread through the rump causing a colour change from blue to green.

The inheritance of the mutation is sex-linked. As mentioned earlier, wildtype Peachface Lovebirds have both psittacin and melanin present in their down. The colour is a dark yellow. Roseheaded specimens have a much brighter yellow down, because melanin is lost from it — the typical opaline effect.

The one feature lacking is the presence of a white underwing stripe.

Conures

It has also come to my attention that there exists a mutation that occurs in two separate species of Conures that fits many of the classification points for opaline alleles. It is called Yellow-sided and occurs in Green-cheeked and Black-capped Conures.

In the Green-cheeked Conure, this mutation has the following effects. It removes melanin pigments from the front (throat, chest and belly) of the bird. And it enhances the psittacin pigments through the same area with increase distribution of red pigments. This distribution of red psittacin is highly variable and subject to selection pressure in the same way as psittacin is on opaline alleles in other species. Melanin is lost from the down feathers and the mutation is inherited in a sex-linked manner. One experienced breeder in the USA, Sandi Brennan, describes the melanin loss from body feathers as creating a scalloping effect; strongly reminiscent of the effect I described for Bourkes, Redrumps and Turquoisine Parrots.

I believe the appearance of the mutation in the Black-capped Conure is similar, but have not yet seen a photograph, nor had a detailed description.

Plumhead Parrot

There is also a mutation being established in Europe for the Plumhead Parrot that has the photographic appearance of an opaline allele. It is believed to be sex-linked in inheritance form, but I know little else at present. It does not show wing stripes in the photographs.

Four possible Opalines

We now have four possible new opaline mutations, yet all these new alleles lack one of our identifying markers, the retention and enhancement of white underwing stripes. I can think of two possible explanations for this situation. Firstly, it is possible (and highly likely) that the white underwing stripe was a feature evolved by parrots in Australia and no rudimentary genes for it exist in other species evolving elsewhere. Therefore once again we see a different group of features for the opaline locus in a different group of species, reflecting the differing genomes created through evolution. The second alternative is that this new group represents a mutation at a new sex-linked locus; previously unidentified.

I believe the latter is unlikely, as there still are no examples of two different sexlinked distribution mutations in any species known. (As discussed in my original article, studying recombinant frequencies could give conclusive proof on this issue.) This leads me to believe that it is most likely all these mutations represent alleles of the one locus in different species of parrots. Once again highlighting that the opaline locus truly does fit the title of my previous article:

Different Strokes for Different Birds - part 1

Copyright: Terry Martin, October 1999

If you’d like to discuss this article or any other issue with Terry
he may be contacted at:

sbankvet@bigpond.com

Other articles by Terry Martin:

The nature of the Opaline locus

The Pied (or Olive-Pied) Redrump Parrot

Defining and classifying Fallow colour morphs

Applying a scientific base to our understanding of Parrot colour morphs

Back to Clive’s original Opaline article

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