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Friday, March 31, 2017

Purple Body (Pb) study in Poecilia reticulata, an Autosomal Dominant Gene

© Alan S. Bias and Richard D. Squire
Permission granted for nonprofit reproduction or duplication of photos and text with proper credit for learning purposes only.

March 31, 2017

Homozygous Pb/Pb male

(A) Heterozygous male Pb/pb, (B) Non-Pb pb/pb male

The Purple Body gene is located on an autosome. Breeding tests, involving this modification of orange spotting, reveal this trait to have an incompletely dominant mode of inheritance. As such a formal name and nomenclature of Purple Body (Pb) has been suggested (Bias and Squire, 2017a). [Note: Hereafter Purple Gene, or Purple Body Gene used interchangeably in reference.]

Wild Poecilia reticulata, both in native populations and feral introductions, exist in a previously undocumented polymorphic state; Purple Body and non-Purple Body. In Domestic strains both polymorphisms persist as a direct result of intended breeder intervention and as an unintended result of outcrosses between fixed phenotypic strains. The co-existence of the two phenotypes suggests a selective advantage under predation (crypsis) and in sexual selection (conspicuous pattern) under diverse ambient lighting conditions.

A generally accepted definition of polymorphism states: “(1) Polymorphism is the occurrence together in the same habitat of two or more distinct forms of a species in such proportions that the rarest of them cannot be maintained by recurrent mutation. (2) If a genetically controlled form occurs in even a few percent of a population it must have been favored by selection. (3) Polymorphism may either be transient, in which a gene is in process of spreading through a population unopposed, or balanced, in which it is maintained at a fixed level by a balance of selective agencies. (4) Owing to the recurrent nature of mutation, transient polymorphism is generally due to changes in the environment, which make the effects of a previously disadvantageous gene beneficial (Ford 1945).”

The violet-blue chromatophore unit and removal of xanthophores by Pb modification is required to produce an all-purple phenotype. The Purple gene has the ability to modify extent genome-wide chromatophore populations in heterozygous and homozygous condition, with increased visibility in the UV spectrum. As a result, this demonstrates selection favoring short “private” wavelength signaling.

Pb is now identified as the first polymorphic autosomal gene to be described as existent in high frequencies in wild, feral and Domestic Guppy populations. It is capable of pleiotropic effect on all existing color and pattern elements at multiple loci. It should therefore be considered a strong candidate for further studies involving “relationships between spectral and ultra-structure characteristics” in orange ornamentation, and extending to color and/or pattern as a whole as suggested by Kottler (2014). A mechanism is identified by which Pb is capable of balancing overall color and pattern polymorphisms, in turn providing fitness through heterozygosity in diverse complex habitats.

(A) Homozygous Pb (Pb/Pb) modified ornaments, expressing removal of xanthophores and increased violet-blue iridophores. (B) Homozygous Pb (Pb/Pb) modified ornaments, expressing reduced xanthophores and increased violet-blue iridophores. (C-D) non-Pb ornaments (pb/pb) expressing no alteration of xantho-erythrophores.

The following four papers and five supplemental documents are the cumulative result of a 3 1/2 year study by Bias and Squire of the Purple Body (Pb) gene in wild, feral and Domestic strains of Poecilia reticulata. Paper No. 1 - Formal Description, No. 2 - Microscopy Tissue Study, No. 3 - Microscopy Ocular Study, No. 4 - Domestic Phenotype Expression.

Select the "Download Link" tabs below to access screened copies of documents from Cold Spring Harbor Laboratory's bioRXiv preprint server for Biology in .pdf format downloaded to After completion of peer review and publication links will be updated to Poeciliid Research Journal.

1. The Cellular Expression and Genetics of an Established Polymorphism in Poecilia reticulata; “Purple Body, (Pb)” is an Autosomal Dominant Gene (DownloadLink)

S1 TABLE – Condensed Breedings and Results (Download Link)
S2 TABLE – Expanded Breedings and Results (Download Link)
S3 Materials Full Description and Sources (Download Link)

Abstract. Modification of wild-type carotenoid orange and pteridine red coloration and spotting of male ornaments in both wild populations of Poecilia reticulata (Guppies) and modern Domestic Guppy strains by the Purple Body gene has long been overlooked in research articles and little understood in breeder publications. This modification is commonly found in wild-type Poecilia reticulata reticulata populations from numerous collection sites and has been photographed but not recognized in these collections. It is non-existent or near absent in collections taken from variant populations of Poecilia reticulata wingei. We identify and determine the mode of inheritance, cellular and phenotypic expression by the Purple gene in these stocks. The Purple Body color pigment modification is a distinct polymorphism in wild P. reticulata reticulata populations. Its existence suggests multiple benefits that satisfy female sexual selection preferences, and minimize or reduce potential predation risks. Photographic and microscopic evidence demonstrated that Purple Body is a normal polymorphism in wild and domestic guppies modifying color pigment regions. Purple Body is inherited as an autosomal incompletely dominant trait.

2. The Cellular Expression and Genetics of Purple Body (Pb) in Poecilia reticulata, and its Interactions with Asian Blau (Ab) and Blond (bb) under Reflected and Transmitted Light (Download Link)

S1 Materials; Slide Specimen Photos (Download Link)

Abstract. Mature Purple Body and Non-Purple Body male guppies differ from each other in several ways. Non-Purple males may have large numbers of xanthophores, erythrophores, and blue iridophores, in addition to the usual dendritic, corolla and punctate melanophores. Fewer violet iridophores are found. In contrast, homozygous Purple Body males lack collected and clustered xanthophores, although isolated single xanthophores remain. Violet iridophores and blue iridophores (violet-blue chromatophores units) abound. The dendrites of dendritic melanophores are finer and form chains with each other. Punctate and corolla melanophores in areas comprising orange ornaments are greatly reduced in number. The heterozygous Purple Body male has erythrophores similar to those of non-Purple males, but yellow pigment is reduced. The melanophores are not as greatly changed in orange ornaments. In Domestic Guppy strains, and at least in one suspected instance in wild-type, melanophore structure and populations may be further modified by one or more additional autosomal genes.

3. The Cellular Expression and Genetics of Purple Body (Pb) in the Ocular Media of the Guppy Poecilia reticulata (Download Link)

S1 Materials; Slide Specimen Photos (Download Link)

Abstract. Our study revealed the presence of all major classes of chromatophores (melanophores, xanthophores, erythrophores, violet-blue iridophores, xantho-erythrophores) and crystalline platelets in various combinations in the iris and ocular media (cornea, aqueous humor, vitreous humor, outer lens membrane) of Poecilia reticulata. This novel ocular media study of P. reticulata takes into account the distinct interactions of Purple Body (Pb) based on results of previous Bias and Squire Purple Body (Pb) publications. Taken in conjunction with other researcher’s published results (regarding UV reflected color and pattern, vision, mate choice, individual preferences, and opsin capabilities) this indicates that these ocular chromatophore populations together create a complex ocular filter mechanism. This mechanism in turn provides spectral capabilities into the UV and Near-UV wavelengths in both Pb and non-Pb individuals. The chromatophores in the cornea, aqueous humor, covering membranes of the lens, and the vitreous humor comprise an ocular filter system that could reduce UV damage to the internal structures of the eye. The guppy’s ability to use UVA as a visual component provides a “private signally system” that cannot be detected by some predators. While non-Pb guppies should derive benefit in the near-UV from violet-blue iridophore units, greater benefit will be derived by Pb individuals with more violet iridophores functioning in the lower UV and near-UV wavelengths. To our knowledge little has been published for P. reticulata concerning pigmentation within the guppy eye. Macroscopic and microscopic imagery is presented.

4. The Phenotypic Expression of Purple Body (Pb) in Domestic Guppy Strains of Poecilia reticulata (Download Link)

Abstract. Modification of wild-type carotenoid orange and pteridine red coloration and spotting of male ornaments in modern Domestic Guppy Strains (Poecilia reticulata reticulata) by the naturally occurring Purple Body gene (Pb) has been long incorporated into their strains by Pedigree Stock Breeders. It is inherited as an autosomal incompletely dominant trait. Its existence has allowed breeders to produce a vast array of Purple based phenotypes. Photographic evidence demonstrates that Purple Body is a normal polymorphism in domestic guppies modifying color pigmented regions. When combined with currently used mutant genes such as Albino, Blond, Golden, Asian Blau, Coral Red, Magenta, Grass, Moscow, Pink, Platinum, Red Mosaic, Multicolor, and Full Red, startling new phenotypes are created. The recently described Purple Body gene (Bias and Squire 2017a, 2017b, and 2017c) has long been overlooked in research articles and little understood in breeder publications.

IFGA Purple Delta, photo courtesy of Terry Aley

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