UPDATE: The butterfly is this post is actually a color mosaic, rather than a true gynandromorph. Click here to read the corrected information on this photo and the butterfly it shows.
A few weeks ago, reader Sandy Sisk sent us this photo of a butterfly that was, well, a little unusual to say the least. Take a look:
Nope, there’s no photoshop or other human trickery going on here – this butterfly is what’s known as a gynandromorph, an organism that displays both and female characteristics. More than that, this particular butterfly displays bilateral asymmetry, meaning one half is male and the other half is female. This strange phenomena occurs most often in insects, crustaceans, and birds, but it’s definitely pretty rare. In this case, Sandy had captured an Eastern Tiger Swallowtail with the left half being female and the right half being male. (Note: Not all female Tiger Swallowtails are black, but those in the southern U.S. often display this coloring in an attempt to mimic the toxic Pipevine Swallowtail. Learn more about mimicry by clicking here.
What causes gynandromorphism? The working theory, very simply put, is that it may come from an uneven split of chromosomes during mitosis (cells splitting) extremely early in development. A similar case of bilateral gynandromorphism stole the show at the Natural History Museum in London a few years ago. The scientists there noted that the butterfly in question (a Great Mormon from Asia) had its reproductive organs fused down the middle, half male and half female, so their ability to reproduce is very unlikely.
Bilateral gynandromorphism has also been noted in other species, notably lobsters and birds like Northern Cardinals and chickens. (Click here to see more photos and learn more about the phenomenon.) However, it hasn’t been observed in mammals and other higher orders of animals, including humans, due to differences in the way these animals develop. Gynandromorphism is estimated to happen to about 1 in every 10,000 butterflies, but since most butterflies look the same whether male or female, it generally goes unnoticed.
We’re glad this example didn’t go unnoticed, and grateful to Sandy for sharing her photo with us! Have you ever seen an example of gynandromorphism in the wild? We’d love to hear about it!