Puzzling Animal Mosaics– and 50/50 male/female gynanders
When I was in Shillong (North-East India) during my sabbatical year, the Director of the local Entomological Museum showed me some of his “treasures” that are normally not seen by the public. He had a golfball-sized elephant dung beetle, pitchblack cicadas, ghostly moths and several hitherto undescribed species of butterflies in his collection. In one of the butterflies, males and females looked very different from each other and the uninitiated would easily have assigned the shorter-winged, somewhat brownish female individual to quite a different group from its swallowtail-like, colourful male. But what I found most fascinating was a specimen of a “halfside gynander” – a term that describes an animal in which one body half (either the left or the right side) is male and the other is female.
Such conditions in which the division between male and femaleness runs along the midline of the animal, have also been described from spiders, beetles and birds. I found this amazing photo of a rooster/ hen gynander on the internet.
Because of the sexual dimorphism, i.e. when males and females look different from each other, such gynanders are, of course, particularly easy to spot among birds and butterflies. Given that these male/female bilateral mosaics can occur in nature, one wonders what causes them and how would such gynander behave. Would the chicken gynander court hens and fight other roosters or would the femaleness dominate? Would the gynander lay eggs? I do not know but the museum director in Shillong believed he had seen a butterfly gynander lay eggs (or at least behave as if it was laying eggs).
As to the cause, the basis of the phenomenon is the natural fusion of two embryos at a very early stage of development, one male, one female. Mosaic individuals (but not separated along the midline as in birds and butterflies) are now routinely produced in mice (referred to as chimaeras) and they even occur among humans, so that cells of some tissues or organs in the body have a different chromosome assortment than the rest of the body’s cells. The earliest experiments to create mosaic animals involved work with newts and salamanders and it goes like this: you have two strains, one normal coloured and one white mutant strain. You need a fertilized egg that has undergone its first division from each strain and you can then create a “mosaic animal”. You have to be a skilful operator, of course, like Nobel prize winner Hans Spemann and his collaborator Hilde Mangold were in the early 1920s, and you need very fine tools. If the two embryonic cells of the white mutant and the normal coloured cells are separated and one pair is swapped and the new white/normal colour combination is permitted to develop normally, the resulting newt larva would be of normal colouration on one side and white on the other. No hoax, no trick, no magic – just Nature’s own miraculous way of doing things exposed through experimentation. Black/white mosaic mice can be created in a similar way by fusing embryonic cells from different individuals, but the result is a patchy black/white mouse and not a half-sided black and white one. However, if you now ask me, why we do not see humans that are male on one side and female on the other as with the rooster/hen photo above, then I suggest on your next visit to the doctor ask if s/he remembers from embryology classes at varsity why this cannot happen in humans. Or does it perhaps and we never hear about it? Be a detective and find out.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2018.
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