Why are some bees green?
Before science, I started out studying journalism. I stuck around long enough to learn some of the basics of collecting information about a story and verifying sources. When working as a photographer for The Daily Nebraskan, I was often tasked with finding freelance photos to fill empty space in the paper. The only text would be a small caption that tried to succinctly address the classic journalistic questions: who, what, where, when, and why (the photo often showed "how"). Who, what, where, and when were easy. They were objective. Then came the "why"...
I remember a photo of a mother pushing her child on a swing close by campus. The young daughter's face showed a mix of terror and glee. After taking the photo, I collected their names and noted the name of the park. But why were they swinging? Oh, probably because the surge of pleasure hormones induced by swinging together would help promote the daughter's positive ideations of her mother, thereby increasing her capacity to form positive relationships well into adulthood. Maybe it is the parent emparting the vital lesson of the necessity of leisure to her young daughter? Maybe they had a big slice of cheesecase after dinner and didn't feel like driving to the gym? Maybe there was no "why"--they just happened upon a swing and they started to swing.
Why are some bees green?
Science shares many commonalities with journalism. "Who" is generally straightforward (although identification of small bees is admittedly a bit of a challenge--is it Agapostemon or Augochlora? What about Augochloropsis? Augochlorella?). "What?" (in a verb sense, collecting pollen; in a noun sense, one could go through Linean taxonomy to group these bees amongust other Halictids) and "where?" (in our yard) are fairly easy. "Why?", on the other hand gets a bit trickier.
I imagine an outdoor dinner party filled with scientists from many diverse disciplines--perhaps a few in the physical sciences, a geneticist, an evolutionary biologist, an ecologist. It is a late summer evening and the light breeze keeps the temperature moderate. As the clatter from the silverwear tinging the dishies begins to lull, a marvelous green sweat bee lands on the floral tablecloth and one of the patrons breaks the silence with "why are bees green?"
The physicist might have a remark about the chemical structure of their exoskeleton, which absorbs some wavelengths of light but reflects others. A perfectly reasonable response that prompts the follow-up question: "but why does this particular bee have an exoskeleton which absorbs non-green pigments and reflects green pigments?"
The geneticist might then conjecture: "well, this particular species of bee is green because the pigment is hereditary, and both parents passed on the allele configuration to this particular green bee that results in a green phenotype." This could be expounded with notions of mutations, favored by natural selection across eons to lead to the modern green bee.
But why are some bees green? If the question has an ecological answer, there must be a functional difference between green and non-green bees. Green bees are polyphyletic, meaning they are not any more closely related to each other than any other two bees. Being green does not imply common ancestry. So...is there something unique about the way green bees interact with their environment? Does green color provide an advantage for green bees because of this unique niche? This would be the phenomenon of convergent evolution. Much like multiple animal lineages evolving wings independently, separate lineages of bees that interact with the environment in similar ways could have independently evolved the green color. Is there something unique about how green bees live and forage compared to non-green bees? Not that I know of. In fact, the color does not seem to have any relationship to social lifestyle patterns (solitary vs. social) or foraging patterns (whether they specialize on gathering pollen from a small group of plants).
There is, of course, the possibility that green bees are green just because they are green. Meaning, they happened to develop a green color at some point in their evolutionary history, but the green pigment has no evolutionary benefit or ecological function. Maybe they are just green.
I think back to the photo of the mother pushing her daughter on the swings. The "why" adds interest. There is curiosity and intrigue. Humans are natural scientists--curious and investigative. We want answers about the world. To be honest, I would love to know why some bees are green. If a bee expert has knowledge of a study I haven't seen, I would love to hear about it. But in the meantime, the key is to not let the obsession over the "why" obscure the beauty of the "who" and "what."
Green bees are pretty neat.
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