Gynandromorphic Chickens: Half-Male And Half-Female

Gynandromorphic Chickens: Half-Male And Half-Female

By Jen Pitino, Idaho

Josephine Joseph was one of several real-life circus sideshow performers cast in the eponymously titled 1932 horror film, Freaks. Josephine Joseph claimed to be sexually split down the center of her body — right side male, left side female. Though Josephine Joseph was prosecuted in the United Kingdom as a fraud for her “Half Woman-Half Man” show, dual-sexed chickens are the real deal.

What is Gynandromorphism?

The word gynandromorph comes from the Greek root words: 1) gyn (which means female; 2) andro (which means male; and 3) morph (which means state or form). A gynandromorphic animal is comprised of both male and female cells. When displayed in a bilateral pattern, the left side of the body will appear to be one sex and the right side the opposite sex.

Gynandromorphism has been reported in insects, birds and crustaceans, but not in other species. In part, this may be due to gynandromorphism not being found in mammals. However an additional explanation for other species gynandromorphs going unnoticed is that the condition is easily recognized in species that are sexually dimorphic (differences in appearance between males and females of the same species, such as coloring, size, shape and structure), such as chickens, but not in species where the different sexes look relatively the similar (e.g. snake, frogs, etc). Gynandromorphic chickens will have a longer wattle, more muscular body structure, masculine plumage and even a spur on the male half of the bird, yet will display female physical body traits on the female half.

The male-female cell split in gynandromorphs is not always down the center of the creature. There are actually four different gynandromorphic patterns in which the split female and male cells can be displayed. Bilateral gynandromorphism is the common left/right split down the center of the animal. Polar gynandromorphism is a front/back split of the body’s female and male cells. Oblique gynandromorphism is an x-shaped division of the female and male cells. Lastly, mosaic gynandromorphic patterning is distinguished by a random mélange (often looking spotty) of the female and male cells throughout the body.

Though an uncommon phenomenon, gynandromorphism in chickens is not an extremely rare condition. It is estimated the roughly one in every 10,000 domestic chickens is a gynandromorph.

Gynandromorphic Chickens
Gynandromorphic Chickens

Avian Cell Development Unique From Mammals

The root cause of gynandromorphism in chickens was greatly misunderstood until recently, when three bilateral gynandromorphic ISA Brown chickens were found on a poultry farm and shared with researcher Michael Clinton, a developmental biologist at the University of Edinburgh.

Until Dr. Clinton’s study, it was widely assumed that sexual development in birds generally followed that of mammals. In most mammals (including humans), hormones are the key to sexual determination. Mammalian embryonic cells (“somatic cells”) start off being generic and unisex. It is not until the gonads (testes in males and ovaries in females) begin developing and secreting hormones that sexual cell assignment in mammalian embryos occurs. In other words, sex hormones drive the female or male determination of cells in mammals.

Dr. Clinton’s research on the three gynandromorphic chickens revealed that chicken cells, unlike mammalian cells, develop their own sexual identity just 18 hours after fertilization. Consequently, chicken cell sexual determination is independent from the gonadal hormones.

Unlike humans (where females have two X chromosomes and males have an X and a Y), birds have Z and W chromosomes (males have two Z chromosomes and females Z and W). Clinton’s research team took blood and tissue samples from the opposing sides of the three gynandromorphic chickens and compared the samples. Clinton expected to find that the sex-identified cells would be neatly split from one side to the other in these bilateral gynandromorphic birds. However, tests revealed that there was a mixture of both male and female cells throughout these birds’ bodies. The predominance of ZZ (male cells) on one side and ZW (female cells) on the other side accounts for the split appearance in these birds.

What Causes Gynandromorphism In Chickens?

Despite ongoing research scientists still do not fully understand what causes gyandromorphism in chickens. Originally Dr. Clinton and his colleagues hypothesized that avian bilateral gynandromorphism was the result of some chromosomal anomaly or mutation in the two cell stage of embryonic development. However, since discovering the existence of both ZZ and ZW cells in the test subject chickens, the prevailing theory is now that bilateral gynandromorphism starts at the very beginning of cell development through polyspermy, when two separate sperms fertilize a single ovum.

Can Gynandromorphic Chickens Reproduce?

The three gynandromorphic chickens Dr. Clinton studied interestingly did not have the similarly sexed gonads. Test subject bird called “G1” had a testis-like gonad on the left side; test bird “G2” had an ovary-like gonad on the leftside; and test bird “G3” had a swollen ovo-testis (like those found commonly in sex-reversed hens) on the left side of its body. G1’s testis-like gonad primarily was composed of sperm in tubules; G2’s ovary-like gonad was primarily composed of large and small follicles (ovarian follicles contain immature ovum); and G3’s ovo-testis gonad was comprised of a mixture of empty tubules and small follicular-like structures.

In spite of their gonads, G1, G2 and G3 were sterile, which is typical in gynandromorphs. A gynandromorphic chicken however, might still be able to produce eggs. In chickens, only the left ovary is functional. Consequently, if a bilateral gynandromorphic chicken was predominantly female on its left side, it might be capable of laying eggs. Conversely, a right-sided female bilateral gynandromorphic chicken would never be capable of producing eggs.

Interestingly, gynandromorphic birds have occasionally exhibited gender behaviors. Test bird G1 seemed to think that it was a male, according to Dr. Clinton. Similarly, a gynandromorphic finch studied by a different research group noted that the bird sang the masculine song, courted and copulated with a female finch but the pair only produced infertile eggs. One proposed explanation for this gender identification in these sexually split birds is the possible predominance of male brain cells or male hormones in these birds.

The fact that there are many species that are not sexually dimorphic begs the question whether gynandromorphism is more common than previously suspected because such differences may not be easily observed.

Gynandromorphism is not the same as:

Hermaphrodism. Hermaphrodism is when an organism has both male and female reproductive organs, but may not exhibit any other external characteristics of being dual-sexed. In gynandromorphs, the animal has only one reproductive organ, but its dual-sexed body cells will typically be externally noticeable since one half of the body will look characteristically female and the other half male.

Chimerism. Chimera is a condition by which an organism originated from two (or more) fertilized eggs merging into one during embryonic development. In other words, it is essentially when one non-identical twin embryo absorbs the other. Chimera can look like gynandromorph as the organism exhibits distinctly different traits on opposite sides of its body. An interesting side note: although there are no confirmed cases of gynandromorphism in humans, there are verified cases of chimerism.

• Sex-reversal. Spontaneous sexreversal occurs in hens when their left ovary fails and a subsequent hormonal imbalance triggers the development of the dormant, undetermined gonad on the right side of the bird into an ovotestis. An ovo-testis has characteristics of both male and female genitalia. The sex-reversed hen will develop physical and behavioral male characteristics (e.g. growth of spurs, sickle feathers, longer wattles, crowing and even mounting of hens). The transformation of the sex-reversed hen will be evenly developed on both sides of the bird’s body. Moreover, the sex-reversed hen will remain genetically a female despite her transformation.

Sources

“Gender-Bending Chickens: Mixed, Not Scrambled.” SciLogs RSS. Published March 12, 2010. http://www.scilogs.com/maniraptora/gender-bending-chickensmixed-not-scrambled/

“Gyandromorph v. Hermaphrodite.” Minnesota Bird Nerd RSS. Published January 10, 2009. http://minnesotabirdnerd. blogspot.com/2009/01/gynandromorph-vshermaphrodite. html

“Gyandromorphs – Breaking All the Rules.” Science Snaps RSS. Published March 19, 2013. https://sciencesnaps.wordpress. com/2013/03/19/gynandromorphs/

“Half-siders: A tale of two birdies.” Guardian RSS. Published January 31, 2014. http://www.theguardian.com/science/grrlscientist/2014/jan/31/grrlscientist-halfsider-chimera-bilateral-gynandromorphbirds

“Josephine Joseph.” Wikipedia RSS. Last Modified on May 22, 2015. http://en.wikipedia.org/wiki/Josephine_Joseph

Parry, Wynne. “Strange Birds Present Gender-Bending Mystery.” Live Science RSS. Published May 26, 2011. http://www. livescience.com/14209-gynandromorphbirds- genetic-anomaly-sex-identity.html

Schenkman, Lauren. “No Sexual Confusion for Chicken Cells.” Science Mag RSS. Published March 10, 2010. http://news. sciencemag.org/biology/2010/03/no-sexualconfusion- chicken-cells

Yong, Ed. “Every cell in a chicken has its own male or female identity.” Discover Magazine RSS. Published March 10, 2010. http://blogs.discovermagazine.com/notrocketscience/tag/gynandromorph/#. VWx_jtJViko

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