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Sunday, February 25, 2024

WHY DO GREEN-BLUE-PURPLE GUPPIES SUDDENLY APPEAR IN DEDICATED STRUCTURAL COLOR BREEDINGS?

Have you ever wondered why Green-Blue-Purple Guppies suddenly occur in your dedicated breedings for a single color?  It’s all in the genotype…

Green Delta (pb/pb) and (Mgmg), expressing VEG modified to blue.

© Alan

© Alan S. Bias
Permission granted for nonprofit reproduction or duplication of photos and text with proper credit for learning purposes only.
February 25, 2024

International Fancy Guppy Association (IFGA) Green-Blue-Purple delta form a “continuum” of interrelated structural color expression.  Other than Y-linked orange peduncle ornaments, each lack sex-linked xantho-erythrophore (yellow-orange-red) color pigments in their body and finnage.

Structural color derives from a thin basal layer of violet-blue iridophores and melanophores residing in close proximity forming chromatophore units.  Actual expression is influenced several factors, including the ratio between violet and blue iridophores.  Further influenced by diversity in angles of crystalline platelets, which act as mirrors, residing under the violet-blue iridophore layer.  In conjunction producing variations in perceived color, i.e. green or blue-green or blue or blue-purple or purple depending upon angle of ambient light source.

(A) Heterozgyous Pbpb modified Dendritic melanophore-iridophore chromatophore units. (photo), and (B) Non-Purple Body (pbpb) Dendritic melanophore-iridophore chromatophore units.  (100X non-dissect, reflected lighting).

The primary genes at play include, but not limited to:  Purple Body (Pb), Metal Gold (Mg), and Vienna Emerald Green (VEG).  Each of which are conserved across multiple teleost species.

I.  Purple Body is a confirmed autosomal incompletely dominant gene that expresses in ratios of (1:2:1) in genotypes (pbpb : Pbpb : PbPb).  Which equates to (non-Purple Body : heterozygous Purple Body : homozygous Purple Body).  What this means is in perfect ratios, if all offspring survive to maturity, 1 out of 4 will be pbpb, 2 out of 4 will be heterozygous Pbpb, and 1 out of 4 will be homozygous PbPb.


Purple Delta (Pb/-) modified ornaments, expressing VEG, reduced xanthophores and increased violet-blue iridophores.

Pb has visible effect in heterozygous expression and amplified effect in homozygous expression. In heterozygous condition formation and migration of xanthophores which result in yellow color are inhibited. In homozygous condition formation and migration of xantho-erythrophores which result in yellow-orange-red color are inhibited.

Pb is often present in both Green and Blue.  Pb is always found in all-purple fish, but is not by itself sufficient to produce the all-purple phenotype in heterozygous Pbpb expression or homozygous PbPb expression.  While Violet is a true wavelength color, Purple is a composite produced by combining blue and red wavelength colors. Further removal of xantho-erythrophores, in conjunction with both increased populations and/or the visibility of modified melanophores and naturally occurring violet-blue iridophores, is required for production of the all-purple phenotype.

II. Metal Gold appears to be an autosomal incompletely dominant gene which would express in ratios of (1:2:1) in genotypes (mgmg : Mgmg : MgMg).  Which equates to (non-Metal Gold : heterozygous Metal Gold : homozygous Metal Gold).  What this means is in perfect ratios, if all offspring survive to maturity, 1 out of 4 will be mgmg, 2 out of 4 will be heterozygous Mgmg, and 1 out of 4 will be homozygous MgMg.

Mg has visible effect in heterozygous expression and amplified effect in homozygous expression. Though harder to quantify, in heterozygous condition formation and migration of xanthophores which result in yellow-gold color are often limited to specific regions of the body, such as the central caudal base, the dorsal and specific regions of the body.  In homozygous condition the entire body appears to be additionally covered by a yellow-gold cast.  As seen in Apple Green phenotypes.

IFGA Apple Green delta (MgMg), photo courtesy of Bryan Chin.

Mg is present in both Green and to a lesser degree in Blue. However, Mg is absent or masked in Purple. Mg expression is greatest in pbpb, i.e. non-Purple Body, reduced in Pbpb, i.e. heterozygous Purple Body and non-expressed or masked in PbPb, i.e. homozygous Purple Body.

III. Vienna Emerald Green is reportedly passed by Y-link mode of inheritance, though I have seen several instances of potential X-link in breeding tests.  VEG is most visible as a central green spot at the peduncle-caudal base, though should be considered a full body modifier that exerts influence body wide.


Vienna Emerald Green (VEG) Peduncle Spot.

VEG expression is greatest in pbpb, i.e. non-Purple Body, reduced in Pbpb, i.e. heterozygous Purple Body and non-expressed or masked in PbPb, i.e. homozygous Purple Body.  VEG expression is easily modified from green to blue.

Solid structural colored fish did not just occur in a single event or in rapid fashion to suggest they result from a single dominant gene.  Rather, the result was a long cumulative breeding process in which color pigment genes were removed and visible Variegation (Var) in the dorsal and trailing edge of caudals persisted for many generations.  Suggesting “solid” is an actual phenotype in which Var is still present and masked.  Being comprised of multiple small mutations in co-expression.

Such a hypothesis is supported by anecdotal evidence.  Primarily in the form of visible results from outcross breedings of Green-Blue-Purple to unrelated fish outside of this color spectrum.  Resulting F1 offspring always express Var to different degrees in body and finnage.  Further support is garnered by another simple observation that is indicative of the continued presence of Var in solid colored fish.  That being, solid colored Green-Blue-Purple fish always express a “black trailing edge” in the caudal and dorsal comprised of motile melanophores.  Which is suggestive of chromatophores needed to produce Var pattern being disrupted in co-expression and further repulsed to exterior edges of finnage.  Together, each supports solid colored Green-Blue-Purple fish being a true phenotype comprised of multiple gene expressions accrued over time.  


(A) Green Delta expressing Pb modified ornaments (Pb/pb) and (Mgmg). (B) Green Delta (pb/pb) and (Mgmg), photos courtesy of Bryan Chin. Note the deepening of the orange body spots.  Both males are expressing VEG.

(A) Blue Delta expressing Pb modified ornaments (Pb/pb) and (Mgmg). (B) Blue Delta (pb/pb), photos courtesy of Bryan Chin. Note the deepening of the orange body spot to pinkish-purple with Pb through xanthophore removal (arrows).  Both males are expressing VEG.

(A) Purple Delta (Pb/pb) males. Results of a homozygous Green (pb/pb) male x homozygous Purple (Pb/Pb) female breeding. (B) Homozygous Purple (Pb/Pb) male x homozygous Green (pb/pb) female breeding. This type male will express as either blue or purple depending upon the angle of light. Note partial modification of orange ornaments to pinkish-purple and increased violet iridophores (red circles).  Both males are expressing VEG.


In summary, zygosity dependent, the presence or absence, and concentration of Purple Body, xanthophores, and erythrophores is the primary distinction in spectrum between IFGA Green-Blue-Purple structural colored phenotypes.  


References:

Bias A. S., Squire R. D., 2017 The cellular expression and genetics of an established polymorphism in Poecilia reticulata; “Purple Body (Pb)” is an autosomal dominant gene. Poec Res 7(1):1-32.

http://www.pr.bioflux.com.ro/home/volume-7-1-2017/

Bias A. S., Squire R. D., 2017 The phenotypic expression of Purple Body (Pb) in domestic guppy strains of Poecilia reticulata. Poec Res 7(1):125-146.

http://www.pr.bioflux.com.ro/home/volume-7-1-2017/


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