The Parblue Puzzle

Part 1 — The Background

A number of parrot species have mutant colour varieties in which yellow ground colour pigmentation has been completely suppressed so that those areas of feather which are green in the normal, or wild-type bird, are seen as blue; and any areas which were yellow become pure white. In addition, other varieties have arisen, sometimes in the same species, in which yellow pigmentation is merely reduced to a greater or lesser extent resulting in varieties variously referred to as Marine, Turquoise, Seagreen, Aqua, etc. These various colour forms have frequently been a source of confusion to many breeders. Only fairly recently has a greater understanding of the mechanisms involved become apparent.

Where yellow pigmentation is completely eliminated the variety is correctly called the Blue. The most commonly bred Blues are those of the Budgerigar and the Black Masked Lovebird, although others are gaining in popularity as they become more accessible. Amongst these the Blue Ringneck is a bird of exquisite beauty where space and noise present no problems, whilst those in more restrictive surroundings may aspire to the blue form of the Splendid Parakeet; the White Breasted Blue.

Sources of confusion

In those cases where yellow is reduced, but not completely eliminated, the variety may be technically described as Parblue (part-blue). However, because breeders are rarely of a technical nature, the names which have become popularised for the Parblue varieties of many species invariably reflect either the visual appearance taken on by that particular species or, with varying degrees of wish fulfilment and ignorance, a romanticized name which includes the magic word, Blue. So the breeder of Splendids, in calling his bird the Seagreen, graphically describes its appearance whereas the other who calls his Peach Faced Lovebird a Whitefaced Blue should, to take a charitable view, have taken his rose-tinted spectacles off.

Besides having an illogical and confusing set of names the Parblue varieties also cause difficulty because it it is frequently difficult to sort out the true nature of their inheritance. In part this is due to wide variations in the amount of yellow, and hence different hues of blue-green or green-blue, expressed by different individuals even though they may have the same basic genetic constitution. This is probably most evident in strains of exhibition Budgerigars which have been selectively bred for many different attributes, over many generations, and as a result carry a heavy burden of mutant genes; made evident by wide variations in size, colour, and feather texture.

Nevertheless, Budgerigar breeders have always included amongst their number those few with a real interest in genetics, knowledgeable enough to carry out investigations and interpret the results. Perhaps even more importantly, they have been willing to air their views and argue their case in the avian press. Consequently, although there are more Parblue varieties in the Budgerigar than in any other species, as well as a true Blue, the genetics have been sorted out and a coherent theory developed. (It should be noted that the information contained in Genetics for Budgerigar Breeders on this subject is very much out of date.)

Despite that example, the situation is less clear-cut with many other species. In general, specialist breeders of many of these species seem reluctant to commit themselves to print with detailed information. And, on the face of it no one would be better qualified to provide answers than the originator or developer of a new colour variety or the first few breeders to acquire stock. Unfortunately, information seldom seems to come from any of these sources. This may simply be due to doubts about their own expertise in this area. On the other hand it may be that, for what we may call commercial reasons, they wish to keep to themselves whatever knowledge they have gained. The consequence is that once the initial founding stock is paired to other (possibly similar) varieties from different sources, the genetics may become much more difficult to unravel. Though there are a few honorable exceptions, this does mean that there are large gaps in the information available and few definite statements can be made.

One such notable exception to this generality is George Smith who, writing in the April 1992 issue of the Parrot Society magazine, described his experiences with what he calls the Turquoise variety of the Ringneck parakeet. Parallels were drawn between this Parblue Ringneck and the similar colour forms which appear in the Alexandrine, Peach Faced Lovebird, Redrump, Blue Fronted Amazon and, in particular, the Budgerigar.

It might also have been topical to mention what are, at the present time, possibly the most widely bred Parblue varieties amongst the Parrot Society membership; the Seagreen and Pastel Blue varieties of the Splendid Parakeet. It was the questions raised in my mind by this article which prompted me to collect my thoughts on this subject together and present them for others to consider.

Remarkable similarity

One striking thing the all-round aviculturalist soon learns is the remarkable similarity in many of the mutant colour forms which occur in the different bird species and genera. This is especially true of the parrots which, with a few exceptions, share the same basic colour make up. A number of readily identifiable colour forms (Cinnamon, Ino, Dilute, Grey, Dark, etc.) turn up with such regularity, and with the same patterns of inheritance, that it is hard to avoid the conclusion that there is some common connection.

Looking at the many varied and distinctive variations in the natural plumage of the parrots it is sometimes difficult to accept that they are built up from just three elements: First, a ground colour of yellow, often accompanied by orange and/or red; second, areas of feather with a peculiar internal structure (the cloudy layer), which produces blue colouration; and third, melanin pigmentation responsible for blacks and greys (sometimes browns), which may be further subdivided into foreground and background melanin.

All three of these elements are required to produce the green of the typical parrot. Where feathers contain a cloudy layer, in association with background melanin, blue is produced. And, if these feathers also contain yellow pigmentation, the blue is modified to green in a way familiar to anyone who has dabbled with paintbrush and paper.

Having accepted that all these parrots inherit very similar colour production mechanisms, it seems justifiable to conclude that these have descended almost unchanged from those so successfully developed millions of years ago in the ancestral parrot. And furthermore, in view of the regular occurrence of seemingly identical colour modifiers, that broadly similar sets of genes control the complex biochemical pathways which culminate in the production of the three colour elements.

In contrast, the patterns of colour distribution have diverged in spectacular fashion in response to environmental and other factors leading to dispersal and speciation. Here, it can be assumed, each species has developed a much more individual set of controlling genes. Despite this we have the example of the opaline gene, which alters colour distribution in the Budgerigar, also appearing in other Australian parakeets and pointing to the probability of a lingering special relationship between these compatriots. (See article The Opaline Factor in Australian Parakeets in these pages.)
 
Even where, in a species or genera, the means to produce a particular colour has been lost or disabled (for example blue in the cockatoos) we can suppose that the rest of the network of biochemical pathways remains unchanged. More controversially, there has been speculation that redundant remnants of a defective or disabled network might still remain; ready to be reactivated by reverse- or back-mutation. So. for instance, a few enthusiasts harbour hopes of producing a Cockatiel showing green and/or blue. (See article The Olive Cockatiel on these pages.) This seems unlikely however, since once these species had lost the ability to produce blue for whatever defect in that particular biochemical pathway, there would have been no further selective pressure to preserve its integrity and a consequent likelihood of further degeneration.

And yet different

Returning to the Parblue genes, it comes as something of a disappointment to find that, unlike most other mutant colour genes they do not appear to fit into the nice general pattern. True, all the Parblue genes appear to be part of a multiple-allelic series in which the blue gene (when it exists) is the most recessive and the normal green gene is dominant, but here the similarities end and each species offers its own variation upon this theme.

This paradox is brought into focus by George Smith‘s experiences with the Turquoise Ringneck parakeet. His breeding results lead him to assert that there are two forms of this variety, one which possesses two parblue alleles and another which has just one parblue allele in association with a blue allele. Of these, it is the single-factor Parblue which produces the least yellow and therefore appears more blue. The explanation offered is to suppose that each parblue gene allows the production of about 25% of the normal amount of yellow, resulting in the single-factor bird having a depth of yellow colouration about 25% of normal with the double-factor having about 50% of normal. That is, in the Ringneck the parblue gene can be thought of as being yellow producing.

Unfortunately , this is diametrically opposite to what we know to be true in the Budgerigar. Here a series of parblue genes, at least two and probably three, produce the Yellowface varieties. Each of these genes is more effective at reducing the production of yellow when present in double-factor form, leading to the conclusion that they are yellow reducing genes. In fact, the Mutant 1 parblue gene is so efficient in this respect that the double-factor Yellowface Mutant 1 has no yellow at all and is identical in appearance to its true Blue counterpart. Only its breeding potential serves to reveal its real identity.

In order to understand the action of the parblue genes, and highlight such differences between species, we do need to go into some basic genetics. This will form the subject of Part 2 of this article.

End of Part 1

Copyright: Clive Hesford, 1992 and 1998

Forward to Part 2

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