Bilateral gynandromorphs! So great! The greatest! Just look at them! Right down the fucking middle, but still completely functional as individual organisms! Nature is awesome!
Non-disjunction, what’s your function? Providing us with some very striking creatures! That is the correct answer!
So, we all know about bilateral gynandromorphs, right? Riiiiiiight? If you don’t, you are going to, because they are the best at everything. Okay, well, maybe not the best at everything. Some of the butterflies with significant species sexual dimorphism might have some trouble flying. But that doesn’t matter, because they could just sit there looking pretty for the whole 2-4 weeks adult butterflies live, and we would bring them things and coo over them and then entomb their corpses in appropriately awesome butterfly mausoleums and okay I guess that one’s a little creepy. But everything that happened before that’s probably pretty rockin’ from a butterfly’s perspective.
Gynandromorphs happen when either something weird occurs during fertilization (two sperm of different sexes making it into the same egg, usually) or when non-disjunction of the sex chromosomes occurs very early on in an embryo’s development. This is scientifically known as “chromosome hogging” and is much frowned upon in polite mitosis circles.
So far, gynandromorphy has been observed in insects, crustaceans, arachnids, and birds. Bilateral gynandromorphs are the easiest to spot for obvious reasons (same deal with gynandromorphy in species with hardcore sexual dimorphism), but mosaic gynandromorphs (last photo is a mosaic gynandromorph) also happen and are much more frequent.
Full disclosure: I discovered this phenomenon at a butterfly theme park (yes, they exist; yes, they are fucking awesome) when I saw the crown jewel of their preserved collection, which happened to be an interspecies hybrid bilateral gynandromorph.
Just take a moment to either let the awesomeness of that sink in or click close-tab because it’s all downhill from here.
Interspecies bilateral gynandromorphy.
If I were a mad scientist, no lie, that is probably what half of my evil genius projects would involve. I would be weaponizing those things day and night. I would be surrounded by technically genetically compatible butterfly species trading awkward looks and puzzling over tiny butterfly bars with tiny butterfly ladies’ nights while I yelled “Breed, my pretties! Breed…for science!” and cackled maniacally. Or maybe cued John Lithgow, my hired maniacal-cackle stand-in, because dude does a good maniacal cackle. (My evil-scientist temporarily-triumphant-speech stand-in would be Tim Curry.)
Anyway, my response to this discovery was to do a little dance and clap my hands and demand to know why no one had told me this could happen sooner, because clearly it’s a thing that happens, until the staff got kind of weirded out and tried to distract me with spiders. Clearly it didn’t work, because I’m writing this, but also clearly it was never going to work because KEEP ON WALKING, SPIDERS, NOBODY LOVES YOU.