COLOR MUTANTS IN ZEBRA FINCHES, Poephila guttata [From: Friends 'N Feathers, M.A.C.B.S.(Mid-America Cage Bird Society), Des Moines, Iowa , Oct 1992]
I have been testing all the color mutants of this finch species that I could get my hands on. My tests are not nearly complete. The number of offspring is low for any one kind of test., and the critical matings are not all made. But since I am going to Brazil for a year, I thought it would be good to summarize what I think I have leaned. My results do not always fit the conclusions found in the books on finches.
One should always start with the wild type. In this species wild type is mostly dark and lighter gray (or bluish according to some). Any mutant in analysis should be compared with this wild type= normal= standard type. Two basic pigments are involved in the feather color; eumelanin, the black or brown color, and phaeomelanin, the red or yellow color. (Adult beaks probably have a different pigment, a type of xanthophyll or carotenoid, although juveniles probably have eumelanin in their beaks.) Wild type color of zebra finches is sex-influenced. Females and males have the tail "barred" (secondary coverts) and an "eye drop" black line vertical from the eye down and slightly curving back to the "chin". A whitish line is in front of it. But only males have the "rusty-red cheek patch, and horizontal "scaling" (black and light lines) on the throat with a heavy black band at the bottom, as well as a chestnut flank with white dots within the chestnut (rusty-red).
One mutant is pied (or piebald) which gives white patches variable in amount and position. It is very easy to miss noticing the variant with white only underneath (ventral), replacing a creamy tan. If the bird is white underneath instead of cream tan, it is probably the result of the pied gene. One variant of pied has a few white flight feathers and a white tail feather or so, often accompanied by small white patches on the head. More often larger white patches are seen. These types are heterozygotes = one dose of the codominant white mutant gene. Two doses are homozygotes, and are entirely white in adult plumage. The juvenile plumage of the double dose pied may show smoky gray especially on the head.
None of the fanciers nor the books I saw told me anything about other kinds of white. So I was surprised to get out of pastel family and related families, a recessive white, that I doubt is the pied type. This is likely to be lost before I can test it properly, since very few are taking enough of my stocks to hold over for my return in a year.
The pastel mutant subdues (dilutes?) the wild type "gray" and whitens the rusty cheek patch on males. It is supposed to be a dominant, but may have dosage effects of the mutant gene. More work is necessary.
The penguin mutant, a recessive, blocks pigment on the extended ventral aspect (underside) like a penguin. So the males have no throat scaling, no chestnut flanks, and no rusty cheek patches. (Even the females have whitish cheek patches?) the heterozygotes may show some small effect, especially in the throat scaling of the male. More work needed!
The light back mutant most notably blocks the "barring" on the tail coverts, so that this species indentification mark is absent. It is a sex-linked recessive. Thus, in a cross with normal (= wild type) females the daughters will be light back (criss-cross inheritance), and all the sons will be normal. But the sons will carry light back (heterozygous) and in a cross to wild type, half their daughters will show light back (hemizygous = one dose only for females in any sex-linked character in birds) and half the daughters will be normal.
Three other sex-linked recessive mutants are known in Zebra finches: brown (= fawn), chestnut flanked, and silver. A probable non- sex-linked mimic of brown (autosomal) may occur as a dominant, but I know little about it. Sex-linked brown is an even, smooth medium brown color in contrast to the wild type dark "gray". The chestnut flanked mutant blocks the black-gray (eumelanin) pigment, except for the eye stripe ("eye drop") and throat scaling, which are much reduced in intensity. So it is often called chestnut-flanked white. Silver is a "diluted" gray with uneven amounts of pigment in the wing feather especially, so that the edges give a mottled effect to the bird (an edge lacing around any one feather).
Interactions of these mutants are interesting in effects. Brown with silver shows a beautiful silver effect with brown edges on the feathers. Chestnut flanked with extra brown or silver reduces the eye stripe to a thinner fainter line. Silver may give a fainter line than brown (more work needed!) Both brown and silver together on chestnut flanked, perhaps, yields no "eye drop". At least, I have had such birds without any "eye drop" that had no other color mutants known. So it is likely, but not proven.
I have tested the brown (b), chestnut flanked (c), and silver (s) sex-linked mutants for allelism, and feel reasonably sure that they are not alleles, but are at different (3) spots on the sex chromosome. I even have presumptive linkage data about how far apart they are. The diagram of order and distance are:
- ----b----9----c---------------27---------------s---- -
This is based on very few offspring, but means that c and s are likely three times as far apart as b and c. So these three should give less than independent assortment.
I needed to "farm out" such matings to have other people help. I did not have many volunteers (hardly any since they were "afraid" of misconstruing scientific work?). So I ended up with 27 mating cages. I could not take enough records or watch their needs well enough, because I was often just feeding, watering, and cleaning. Also no one test got enough effort.
I obtained the penguin, light back, pastel and Florida Fancy from Garrie Landry in Louisiana. He kindly donated them to me for the most part, but part was in trade. "Florida Fancy" is a bright white finch with rusty cheek patches and chestnut flanks, but no throat scaling. So I wanted to find out what mutants it had. I found the brown-silver combination right away, but some birds were diluted (lightened) or whitened a bit. Later I found the absence of throat scaling. So now I have some brown-silver males without throat scaling--beautiful birds. I really expected it to include chestnut flanked which it resembles a lot, but did not find it. While tests are tentative and incomplete, I feel that the Florida Fancy has 4 mutants for color: brown, silver, throat-scaleless, and "dilution".
From Landry I also got yellow bill (recessive) and crested (dominant). I have still to test whether or not crested in Zebra finches is as in canaries--a codominant lethal! ....W. J. Miller, Ames, Iowa; firstname.lastname@example.org