Extremely Rare Half-Male, Half-Female Bee Found In Panama

Krichilsky et al., Journal of Hymenoptera Research, 2020

In the neotropical forests of Panama, researchers stumbled across a truly unique bee: the left side of its body is male, while the right is female. 

Reporting the discovery in the Journal of Hymenoptera Research, scientists led by Cornell University discovered this unique Neotropical bee Megalopta amoena while studying nocturnal bees in the forest of Barro Colorado Island, Panama.

The specimen is known as a bilateral gynandromorph; when the two halves of the body appear to express different sexual characteristics. While the extremely rare condition has been observed in numerous animal species, including at least 140 bee species, this is the first time it’s been documented in this species of nocturnal bee.

“Finding the M. amoena felt like striking gold or winning the Darwinian lottery,” Erin Krichilsky, a student from Cornell University and lead author of the study, said in a statement.

Perhaps what’s most stunning about the specimen is how clearly the gynandromorphism can be seen. It's left side – the male side – features a long antenna, a smoother mandible, and a skinny hind leg. Meanwhile, the right side – the female side – has a short antenna, a spikey mandible, and a chunky hind leg. 

Krichilsky et al., Journal of Hymenoptera Research, 2020

The researchers also managed to analyze the bee’s circadian rhythm, its internal clock that coordinates foraging times, in hopes of unearthing how gynandromorphism might affect an animal’s behavior. This revealed that the gynandromorph’s foraging activity started earlier in the day, compared to both male and female bees, and that its busiest periods closely lined up with the behavior of females. This could suggest that the foraging behavior of this species is more closely associated with the right side of the brain. 

You're no doubt wondering, why do some animals have gynandromorphism? Scientists tend to think there are two main mechanisms behind the condition.

Biological sex is determined by the combination of sex chromosomes. For example, in humans and some other species, males have an X and a Y chromosome, while females have two X chromosomes. (In insects, birds and some other species, sex is determined by the combination of Z and W chromosomes, but we'll stick to X and Y in this explanation for simplicity's sake). 

This is determined whether the "successful" sperm carried either an X-chromosome or a Y-chromosome to bind the mother’s egg, which will always have an X chromosome. In one of the mechanisms that create a gynandromorph, two sperms accidentally enter a rare form of an egg with two nuclei, resulting in the embryo to carry both XY and XX cells.

The other mechanisms are believed to occur during the first moments of development. As it begins grows, a male XY cell will undergo mitosis and duplicate its chromosomes, becoming XXYY, before dividing into two XY cell. In gynandromorphs, however, this process doesn’t run smoothly. Instead of dividing into two XY cells, the cell accidentally divides into an X cell and an XYY cell. If this glitch occurs in the earliest stages of development, then it can result in a large portion of the cells being both X and XYY.

It's possible bilateral gynandromorphism occurs more often than we know, and we only notice it when it appears I species that are obviously sexually dimprphic.

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