What is a gynandromorph? Here are 3 facts about these unique creatures

Published: February 13, 2019

Male and Female Cardinals sit together on a snowy rose bush Photo by Betty Shelton/Shutterstock

If you’re an avid birder, you likely have a long list of species you’ve spotted. But we’re willing to bet you’ve never seen a cardinal quite like the one that Shirley Caldwell of Erie, Pennsylvania noticed in her backyard a few weeks ago. According to a report by CBC News, she’s been watching birds snack at the feeders in her backyard for 25 years, but when she saw the two-coloured cardinal, she knew it was something special. The bird, which was bright red on one side and yellow-brown on the other, has since been identified by experts as a gynandromorph. Never heard of it? Here are a few things you should know before adding it to your birding list. 

Gynandromorphs display male and female traits

A gynandromorph describes any organism that exhibits both male and female characteristics. According to Dr. Beren Robinson, an associate professor with the Department of Integrative Biology at the University of Guelph, “gynandromorphs form as a result of different sex chromosomes, or their effects, arising very early during development in different cell lines. As the organism develops, the different cell lines develop different sexual characteristics in different parts of the whole organism.” The two-coloured bird that Caldwell spotted appears to be what’s known as a bilateral gynandromorph, which means the male-female characteristics are split almost directly down the middle. But gynandromorphs can also be more of a mosaic, with patches characteristic of one sex appearing within a body part or trait that’s characteristic of another sex.

Gynandromorphs occur in more than just birds

Gynandromorphs occur in a variety of species, and have previously been identified in crustaceans, spiders and even insects, including mosquitoes and fruit flies. But the phenomena is easiest to spot in birds, like this cardinal, and butterfly species, when male and female wing patterns are dramatically different from one another. In fact, it was the wing pattern that reportedly tipped off a volunteer, who spotted a gynandromorph butterfly while he was emptying the butterfly exhibit’s pupa chamber at Philadelphia’s Drexel University in 2015.

They’re extremely rare to spot in the wild

“I have never encountered an gynandromorphic organism in the flesh,” says Dr. Robinson, who notes that although gynandromorphs occur in various species, discovering one is considered an extremely rare event—especially a bilateral gynandromorph like Caldwell discovered. Determining exactly how rare these creatures are is difficult, since they can simply go unnoticed, however, research published in the Journal of the Lepidopterists’ Society indicated that among the 30,000 butterflies researchers raised, only five were identified as bilateral gynandromorphs. It was easy for Caldwell to see something different about the cardinal in her backyard, because of its distinct colouring. But its a lot more difficult to identify in adult males and females that don’t display sexual dimorphism, which describes different traits through colouring and other features. It’s also possible that most people simply don’t know what they’re looking for, or have even stumbled upon one and simply didn’t realize it.

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