(Photo by Christy Solo for the Illinois Valley News)
This week we once again learn that nature never runs out of amazing surprises! This week we’ll meet gynandromorphs.
The pictured longhorn Amazon ant (Polyergus longicornis) is one example, and no, you aren’t seeing things! This particular ant is extra special because they are a bilateral gynandromorph!
Whew! That’s a lot of syllables to say, “they are half male and half female.” In our ant’s case, the racy red half is female, and the beautiful black half is male.
While rare, gynandromorphism can happen in insects, crustaceans and birds. It’s not always practically perfectly symmetrical bilateral, but for simplicity we’ll just discuss “halfsiders” in this article.
As to the, “How” we’ll use a birdy example: Bird chromosomes are called “W” and “Z.” Males carry two Zs, females ZW. Most likely, a gynandromorph is born when female egg cells develop with two nuclei, one with a Z chromosome, the other with a W.
When that unique egg is fertilized by a male’s double ZZ chromosome, it develops both ZZ (male) and ZW (female) chromosome. And the result is a bilateral gynandromorph.
Let’s back up a bit to “how rare is gynandromorphism?” Because it only happens with insects, crustaceans, some reptiles and birds, sorting out the rarity is a bit tricky.
First, lots of insects and crustaceans go unnoticed their entire short lives. Though more birds are seen and photographed, a bilateral gynandromorph would only be noticeable in a bird species that is sexually dimorphic.
Recent examples include a gynandromorph cardinal (2019) and rose-breasted grosbeak (2020). In both those species males and females look quite different.
When it comes to some of our most common area birds like scrub and Steller’s jays, black-capped chickadees and song sparrows, males and females look identical. So you could have a gynandromorph – a veritable unicorn of birds – right in your own yard and never know it.
When it comes to insects, butterflies win the “documented bilateral gynandromorph” contest hands – or rather wings – down. About one in every 10,000 butterflies is a gynandromorph.
Still, at much better than “one in a million” odds, it might go unnoticed, but as with birds, people love looking at, photographing and even collecting butterflies. They get a lot of attention so gynandromorphs get noticed.
Also as with birds, there are many species of butterflies and moths who aren’t obviously sexually dimorphic so a unique gynandromorph could go fluttering on by unnoticed.
Can gynandromorphs reproduce? The answer is possibly yes. It’s just one of those (to date) unanswerable questions. If gynandromorphs were more common and many could be followed throughout their natural lives, we might get answers.
In the cases of the “halfsider” grosbeak and cardinal, ornithologists believed each of them could breed and lay successful eggs; as with both birds it was their left side that was the female side.
Fun fact: In most species only the left ovary in birds is functional.
So, while there is a lot we do know about bilateral gynandromorphs, there is lots more to learn. Nature is not only full of surprises but likes to keep secrets too.