A gynandromorph cardinal: one half male, the other half female

September 4, 2012 • 9:58 am

Reader Brian Peer sends us a photo of a “gynandromorph” cardinal (Cardinalis cardinalis).  A gynandromorph, as the name implies, is an animal that is part male and part female, with the sex-specific parts usually demarcated cleanly.  Here’s Brian’s description of how he saw the bird:

Your post this morning on Venus the Cat reminded me of a bilateral gynandromorph Northern Cardinal we found a couple years back in nearby Rock Island, IL. I’ve attached several photos of the bird. As you can see, the left side is male and the right female. For two winters the bird appeared at the feeder of a retired high school biology teacher. I was able to observe it on several occasions, and noticed that it didn’t associate with other cardinals, nor did I hear it produce any vocalizations. We attempted to capture it with mist nets so that Rob Fleischer and I could get blood samples for further study, but we caught every bird in the neighborhood except this one! Alas, it never returned the third winter.

And some photos:

This, by the way, is a very graphic demonstration of the differences between males and females, with the brighter color of the male almost certainly reflecting sexual selection (with bright colors presumably advantageous in males because they attract females, but disadvantageous in females because they attract predators).

Now how does this happen? I used to see this sometimes in my Drosophila flies, and we’ve long known how a half-male, half-female fly forms. In flies the sex is determined by the ratio of X chromosome to autosomes.  Flies, like all diploid species, have two copies of every autosome. If you also have two X chromosomes, you’re a female because the ratio of autosomes to Xs is 1:1. If you have one X chromosome and one Y chromosome, your ratio is 2:1 and you’re male.  The Y doesn’t matter here: if you lose a Y chromosome, and hence are XO, you still look like a male, although you’re sterile (the Y carries genes for making sperm).

So to get gynandromorphs in flies, all that has to happen is that one X chromosome gets lost in one cell when the initial cell in a female (XX) zygotes divides in two.  One half of the fly then becomes XX, the other XO, and the fly is split neatly down the middle, looking like the one below.  But gynandromorphs don’t have to be “half and halfs”.  X chromosomes can get lost at almost any stage at development, so flies can be a quarter male, have irregular patches of maleness, have just a few male cells, or even a male patch as small as a single bristle.

Note smaller wings (males are smaller), and presence of sex comb and dark abdominal pigmentation on the right side. The genitals on the ventral side are also part male, part female.

But in birds, unlike flies (or humans), the females are heterogametic: i.e., their sex chromosomes are different (the females are called ZW; and the males are ZZ). I’m not sure whether chromosome loss is involved in the production of this cardinal, or how that loss affects sex determination in birds (in humans, for example, unlike flies, the Y chromosome is important, so XO individuals are not phenotypic males but largely phenotypic females). An article at Live Science on a similar gynandromorph cardinal in Texas offers the following theory, based on the observation that in gynandromorph chickens the female side is the normal ZW and the male side the normal ZZ:

It’s not known exactly how gynandromorphy happens in birds, Arnold said. The predominant theory is that an error occurs in the formation of an egg, which normally carries one chromosome to unite with the single chromosome carried by the sperm. But if an egg accidentally ends up with two chromosomes — a Z and a W — and if this aberrant egg is fertilized by two Z-carrying sperm, the bird that results will have some ZZ cells and some ZW cells, he explained.

That seems unlikely to me because it requires the concatenation of two rare events: an egg carrying two sex chromosomes instead of one (but the normal half complement of autosomes), uniting not with one sperm but with two.

70 thoughts on “A gynandromorph cardinal: one half male, the other half female

  1. As the bird was only observed and never caught and tested, how do you now it’s a true ZZ/ZW gynandromorph? Couldn’t it be a mutation of a single regulator gene for feather color during replication for the first division of the zygote?

    1. Wouldn’t the simplest explanation be that the fertilized egg was genetically female, but the W was lost in the cellular progenitor of the male half? That leaves a ZW female half and a Z male.

      In humans, the analogue would be losing the Y in half of a genetically male embryo. That would leave half the person as an XY male and half as a X (Turner) phenotypic female.

      1. That produces mosaicism– and usually a male phenotype for the most part… not half and half…

        Though I heard of a chimera baby that was a true hermaphrodite from twin fusion and also half black and half white (from a documentary called “I am my own Twin” –I think.) The photo of the child showed a line of demarcation running down it’s center as in the bird.

        I tried to find the photo of the child on the web, but I was unsuccessful.

    2. We only have an anecdotal account, but supposedly the bird behaved differently as well. That would indicate something deeper than a single chance mutation.

      1. I don’t understand what part of this bird doesn’t look “half-female.” The colors are spot on, including the redding around the wing bar and tips of tails feathers, and some peachiness in the upper breast is pretty typical as well. Also, predominately gray is a far better description than predominately brown of any female cardinal I’ve ever seen. The combination of gray and red comes off as rusty, but they are not really brown, ever.

        1. I’m with Sarah and Thanny. We can debate whether to call the coloring in the photo Thanny linked “brown,” “gray,” “taupe,” or “cinereous,” but regardless, it is not the same color as the half of the bird in the article above. In the third photo in the article, it bears some resemblance, as the wing feathers are pictured. However, isn’t it possible this bird had leucism, a form of albinism which is sometimes not complete? It’s too bad they weren’t able to capture the bird to see for sure.

  2. Why would it take two sperm to fertilize a ZW egg? I suspect the journalist has garbled the explanation here.

    I’m no expert, but suppose a single Z-bearing sperm unites with a ZW egg to produce a ZZW zygote. During the first cell division, all three sex chromosomes get duplicated, but one of each triplet gets randomly left out when they pair up for separation into the two daughter cells. So you can end up with one ZZ cell and one ZW cell.

    Or something like that. I’m sure someone here can imagine a workable scenario.

    1. The problem with this scenario is that the chromosomes pair up during mitosis/cell division, so there would be one unpaired chromosome floating around. This would presumably stop the extra from being duplicated. Having one of the two initial daughter cells (the two cells resulting from the cell division immediately after fertilization) somehow lose a sex chromosome is the simplest explanation.

  3. Thanks, Jerry, for posting this piece on gynandromorphy. I learned something great today, thanks to you! Truly, the fascinating biology stuff is far more important and far more interesting than the crank mail.

    The crank mail is simply a reminder of the very real bifurcation of our society.

  4. I have nothing to contribute other than excitement to see my home (Rock Island, IL) being represented on here. Carry on!

  5. Hey, I got a question for you Jerry (though anyone is welcome to respond if you know the answer).

    The phenotype of this bird (and the half-and-half fly) are very obvious on the exterior, and it’s divided cleanly down the middle. But our insides aren’t so symmetrical – the intestines zig-zag all over the place, the spleen falls to one side, the liver lumps on the other, etc. So where would the half-and-half split exist on the other side of the peritoneum?

    This is obviously a developmental biology question, and I have no idea how well the fly model would compare to a mammalian or avian one.

    1. I know that for flies, the interior, at least the cells in the abdominal surface below the cuticle, are divided just the way the cuticle is: right down the middle. But I have no idea about the bird.

      We don’t see gynandromorphis in humans, although they might occur (I don’t know of a case). They wouldn’t be visually obvious because circulating hormones might efface any differences between sections of the body.

      1. Does anyone know how is the feather color in cardinals determined? Is it by presence of ZW vs ZZ or by circulating hormones?

        If I remember correctly, back in college we did an experiment of applying testosterone to chicks and secondary sex characteristics (comb size, I think), where under control of testosterone.

        If the same was true for the plumage color in cardinals, a single-point mutation in a “color-producing” pathway would a more likely explanation.

        Unusual behavior could be well explained by hostility of other birds towards the weird-colored bird.

        1. For several years, I had what looked like male cardinal, with a white head come to my feeders in my yard in N.E. TX. I believe he came in the winter although we have some cardinals year round. He appeard for 3 or 4 yrs & then, sadly, came no more. I called the Audobon society in Dallas & the person I spoke with asked if he could come & see it but he never showed. We live about 90 mi northeast of Dallas. Late this winter, right now, I have the usual goldfinches in their winter brownish coloring at my finch feeder but there is one yellow one with no black cap. When he appeard it was way too early for goldfinches to have their beautiful yellow color and they have not yet turned yellow. It appears that the other goldfinches do not accept him/her but it is at my feeder most every day. I don’t know if it is mutation but suspect it is. Any comments?

          1. Some yellowish birds that may somewhat resemble the goldfinch may winter in your area. Ideas that come to mind are the Ruby-Crowned Kinglet and the Pine Warbler, although neither should be a particularly brilliant yellow like a finch now (or really ever.) The Evening Grosbeak should be distinguishable by size and also has the cap you cite the lack of. It’s possible that it is just a mutation, as you say. I can’t think of much else it could be except some freaky mexican visitor. Your cardinal was almost certainly a partial albino, a rare but not exceptionally rare phenomenon. I’ve never seen a live example but I have seen many preserved.

  6. When I read stuff like this, I cannot help but think: science is six miles deep in the ocean, while religion is still wading in the kiddie pool.

  7. That is truly amazing. Jerry, you said we don’t see gynandromorphis in humans. Does this process happen to any mammals?



  8. This can’t happen in mammals, is my understanding, because a) there are only a couple of genes on the Y chromosome and b) X-inactivation in females ensures that everybody has the same dose of X-linked genes. So individual cells do not know their sex–instead it’s hormones, all hormones, that determine sexual phenotype at the cell level (the couple of genes on the Y affect hormones).
    In birds, though, every cell ‘knows’ its sex genetically and although some phenotypes are influenced by hormones, most are not.

    Th weird thing to me is that I’m quite sure that the first cell division does not determine the left and right halves of a bird )or mammal) embryo.
    Maybe it is just the epidermis?

    1. I haven’t seen this done with birds or mammals, but in frogs, if you kill one cell after the first division, you just end up with a half-size frog. But very shortly thereafter, like at the four-cell stage, killing one of the cells does result in a frog with one quarter of its body missing. The stage at which the embryo’s left/right, front/back order is determined comes VERY early in the development process.

  9. This is very cool, and I was already aware of this phenomenon.

    But are we sure the cardinal pix are legit? In the first two, the non-red side seems ‘way too white. And the 3rd pic suggests the bird moulted?

    Photoshop is a powerful tool. I don’t know enough to know whether the pix are really real.

  10. Another possibility is that you get an aneuploid ZW egg fertilised by a (single) Z sperm, yielding a conceptus that’s initially aneuploid ZZW.

    Stochastic loss of the extra chromosome in the early mitotic divisions will then give a mixture of ZZ, ZW and (the original) ZZW complement. If the aneuploid cells are less viable than euplid cells – hardly a stretch – then these fail to proliferate and are lost, leaving an animal that’s mosaic ZZ/ZW.

    1. Cover the red half of the cardinal and it will look less bright white. Your color perception is getting skewed by the contrast against the bright red.

  11. The right half of the cardinal looks like a normal female to me.

    There are a fair number of photos of gynandromorphs out there: try doing a Google image search for gynandromorph butterfly, moth, beetle, crab, lobster, chicken, finch, cardinal, bird.

    The butterflies and moths are often really spectacular not only because of the striking color differences between males and females, but also wing size and shape and even body size.

  12. Very nice! If you’d like some photos of a bilateral Drosophila gynandromorph, I have some on my webpage…


    As far as the “multiple really rare events” required to produce the cardinal, I think that a much more likely mechanism to produce this bird is chimerism. Start with a single egg that contains two oocytes (we can see two-yolk eggs in chickens, so two-oocyte eggs must happen with some regularity), one of which gets mom’s W chromosome, and the other mom’s Z chromosome. Then early after fertilization, the WZ and ZZ oocytes fuse to form a chimeric blastocyst, with the two clones of cells more or less dividing the organism bilaterally. This sort of chimerism can show up in humans as fetus in fetu.

    An important inference from gynandromorphs is that individual cells in flies (and birds) know whether they’re male or female. Mammals, on the other hand, use hormonal sex determination, so these clones of cells don’t show up so well.

  13. Really amazing and even more so for me because I live in Rock Island, IL. Gynandromorph Cardinals and black squirrels, not bad Rock Island, not bad.

  14. This scrambling could explain how someone with a genetic profile of 75% European, 21% sub-Saharan African, and 4% Indigenous American only gets keloid scarring on some parts of their body and not others.

  15. Hey,

    Fernando Nottebohm found a gynandromorphic zebra finch several years ago, and they performed all kinds of interesting test on it. The article is awesome if anyone is interested.

    Neural, not gonadal, origin of brain sex differences in a gynandromorphic finch

    Robert J. Agate*, William Grisham*, Juli Wade†, Suzanne Mann*‡, John Wingfield§, Carolyn Schanen*‡, Aarno Palotie*,
    and Arthur P. Arnold*¶

  16. Hey,

    Fernando Nottebohm found a gynandromorphic zebra finch several years ago, and they performed all kinds of interesting test on it. The article is awesome if anyone is interested.

    Neural, not gonadal, origin of brain sex differences in a gynandromorphic finch

    Robert J. Agate*, William Grisham*, Juli Wade†, Suzanne Mann*‡, John Wingfield§,

    Carolyn Schanen*‡, Aarno Palotie*,
    and Arthur P. Arnold*¶

    If this posted twice, sorry, I had some trouble logging in.

  17. Here’s an interesting question. It’s obvious that whatever is happening is happening before the first cell division. But does it ever happen after? Can it happen, for example, in the second, leaving the bird 1/4 female?

    And, I also wonder, could it have also happened in theropod dinosaurs? I don’t know much about members of the order besides tyrannosaur, which had pronounced sexual dimorphism which might not have been compatible with life.

    I suppose we shall have to put it on the list of questions to ask when someone develops time travel.

  18. Hi there. I am the owner of Venus the Cat that you mentioned at the start of the article. Brian Peer, Venus is all female (well, at least from outer observation) but you can see the very unique and unusual differences with the whiskers being different colors on each side, odd eyes, half & half face, paws (even underneath half the pads are black while the others are pink, and a straight line down her tummy (even has half pink lip half black & half pink nose half black). Now I know NOTHING about genetics, only what I’ve been told which suggest chimerism with all of those unique things going on. What is your best guess and do you know what would be involved in having her DNA tested to look for 2 strands? I don’t want to have anything invasive done on her but I know (because we know a human chimera) it can take many tries before the second strand is found. Is it as simple as swabs, hairs, etc or more invasive. I’ve done some calling around (even to the University of Florida in Gainesville) and haven’t found anyone who has ever done it or has the experience. I, along with her whole entire fan base on Facebook plus many others would love to know and get down to the answer of exactly what happened in the womb. I thought I would just ask and by the way, the bird is fascinating and gorgeous…shame you haven’t seen him/her again. You can also feel free to email me directly at VenusMommy09@gmail.com

  19. Beautiful bird. Is it possible that this cardinal is leucistic? If you Google leucistic northern cardinal you can find many examples of “piebald” cardinals. There is even an example of a peacock who is “half-leucistic” similar to our friend in the photo here.

  20. In Hindur eligion a concept of this nature is well illustrated in ARDHANARISHWAR, a deity whose left half is a goddes, the right half is the god.

  21. If you google “leucistic Cardinal”, you will see that the variety of photos pretty well wipes out the nonsense about the bird being a gynandromorph. You can’t just look at the bird and call it a gynandromorph.

  22. I, also, have pics of a gynandromorph cardinal that showed up at my feeder in Oklahoma a few years ago. Interesting that every pic I have ever seen of them shows the female on the right side of the bird. A gynandromorph is not necessarily a hermaphrodite. It is possible that it has 2 testes and one of them doesn’t produce male hormones or it may have 2 ovaries and one of them happens to produce male hormones.

  23. I too did Drosophila genetics from 1961 to 2007, raised (myself & my genetics classes) tens of thousands of fruit flys and saw a gynandromorph about every 2-3 years. No reason to think the cardinal is not a gynandromorph, but I’m not convinced it is either. The determinate cleavage mentioned frequently in above comments could also allow a somatic pigment blocking mutation (such as albinsim) to affect one side but not the other. That would explain everything I see in the pictures. We’ll suppose photoshop or an airbrush were not explanations.
    Several good questions about gynandromorphy in mammals (including humans). In mammals a functional gynandromorph is impossible because we get only one set of gonad anlage’ (buds) which can grow into one or the other-but not both. Any problem (genetic, hormonal or traumatic) and both male and female parts of the gonad may grow thus producing an intersex. There have been some mammalian gynandromorphs identified (karyotypic and others) but the gonad is an ovitestis and only a little more testis-like on one side, a little more ovary-like on the other. Functionally no sex.
    With the Drosophila gyndromorphs found in my genetics lab we always tried to breed them, first with a female and then a male. None of those attempts was ever successful – most of them didn’t live long enough to complete both trials…apparently they had some other problems too.
    Drosophila karyotypes are easy to do but unfortunately not with the adult. You need the salivary glands of 3rd instar (oldest) larvum just before they metamorphose into a pupa. Would have been great to compare karyotypes of the left and right glands.

  24. Why does it say ‘the left side is male and the right female’ When clearly it is the opposite. The red represents the male and the tan the female. Obliviously, the author doesn’t know much about birds or they wouldn’t of gotten this very important fact wrong. however, this find is very interesting to say the least.

    1. Are you serious? Have someone take a picture of you with a pin over your heart, and compare the pic to the above. I’m assuming you agree your heart is on the left side of your body.

  25. I found this article via I f*cking love science on FB. In college, I actually worked in a lab for a semester with zebra finches (neuroscience minor) and we had one true gynandromorph and one mosaic. Since the interest here seems genuine I figured I could share my relatively small knowledge from my experience with the birds.

    Originally we thought both were gynandromorphic. The one we found out was mosaic was actually more similarly colored to a regular zebra finch. It had more brown, although the male colored side (striped plumage on chest and bright orange cheek with a black stripe under the eye) was less pronounced and not evenly split down the middle. Some of the stripes went a little past onto what we considered the female side. The one that turned out to be a true gynandronorph had odd coloring for a zebra finch. It had quite a bit of white, but the stripes were very clear and the cheek was a bright orange. These two displayed the typical male behavior of zebra finches (singing, song creation) but when I got into the lab they were already adult and kept separate from the other birds. I never saw how the other animals interacted with them. I know according to the prof I worked with that there were studies and observations of other gynandromoprhs (they are very rare, very few have been born in labs) and they tend to display either male or female behavior even though they are split right down the middle. The ones that display female behavior can lay eggs. I think the males may be sterile though. I’m not sure if zebra finch females can lay unfertilized eggs like chickens.

    When the birds were put down for the experiment, that’s when we discovered one was a mosaic and one was a true gynandromorph. The mosaic had one small and underdeveloped ovary on one side and no matching ovary nor a teste. The gynandromorph had a fully developed ovary on one side and an underdeveloped but present teste on the other. Genetically one showed as a mosaic and one as a gynandromorph (I helped with these experiments but do not know how to understand the results so I can’t explain how the prof determined that). The gynandromorph also had brain activity split right down the middle. When exposed to the songs of male zebra finches, literally one half responded with feminine brain pattern response to the stimuli and one half responded with male brain patterns.
    Again I’m not a Ph.D but that was my experience with them! Maybe it answered a few questions even though this particular article is of a potentially gynandromorphic cardinal.

  26. Thank you so much for this ! I posted one of these photos I got from a Facebook page posting and shared it on my educational blog,giving this site its due credit,of course and also shared the link to it !

  27. http://www.youtube.com/watch?v=LNTGgDk1Yck

    This is a link to a time lapse video a past colleague posted to his YouTube site that was acquired using our automated Leica upright epifluroescent microscope while he was doing his postdoctoral work in our lab at Kansas University Medical Center. This time lapse illustrates how gastrulating cells migrate bilaterally away from each other but then come back together, in this case to form the heart tube, which is populated by cells that originally migrated to opposite sides of the midline of this quail embryo. If the author of this article, Jerry A. Coyne is correct in his hypothesis that there were 2 sperm that fertilized this egg, then the bilateral asymetry of this cardinal can be explained if each side of the animal was populated by a majority of male ZZ cells and the other side was populated by a majority of female ZW cells. This rare bird is an example of why I think gastrulation is a critical event leading to greater diversity in a species.

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