From grapes and bananas to “popping cherries” and “buttering muffins,” food has long been associated with sex. This association may be biological in nature, as research has found that this relationship is not just unique to humans. But finding the direct chemical switch connecting eating and mating has been elusive.
Now, a group of researchers from the University of California San Diego believes that they might have found this chemical switch, and in a surprising location: within the guts of fruit flies.
Background: First Eating and Then…
Holidays like Valentine’s Day or an anniversary often conflate love with food. From giving a woman chocolate to booking a romantic dinner, our society connects eating with passion. Science shows that humans are not the only organisms that do this as other animals offer food (sometimes their own bodies) to their mates before mating. Male bonobos, for example, often give a “nuptial gift” to a female before copulation. This gift may take the form of food. Similarly, the male great gray shrike bird builds up a store or “larder” of food to show off to a potential mate before she picks him. Due to their survival instincts, many females pick males with the best food offering, before copulating with them.
In more extreme situations, the male becomes the food for his potential mate. This behavior is seen in many types of spiders, where the often-bigger female attacks the male while having sex with him. Praying mantises are also a good example of this process, called sexual cannibalism, where the female eats the male’s head. Males can also prey upon their female mates, but it’s much less common, usually due to the female having to give birth later.
Analysis: A Chemical Switch
In order to understand the chemical switches that transition from eating to mating, researchers at the University of California San Diego used fruit flies, as the timing of their courtship process is akin to a speed-dating session. The researchers found that by feeding the flies a protein-rich diet, their guts triggered the release of the signaling molecule diuretic hormone 31, or Dh31. This hormone then signaled to the flies’ brains to switch from eating to mating. The team published their results in Nature.
To validate that Dh31 was the right molecule, the researchers manipulated the genes of some of the files, knocking out the Dh31. These flies continued to eat and did not transition to mating behavior. In separate experiments, Dh31 was activated and the flies immediately transitioned to copulation. According to Dr. Jing Wang, professor of Neurobiology at UC San Diego: “These results indicate that Dh31 is a signaling molecule that reorders the priority of these two contending behaviors: feeding over courtship in the absence of Dh 31 and courtship overfeeding when Dh31 is released in the gut.”
Outlook: Is the Gut Calling the Shots?
Knowing the chemical switch that can change behaviors is important to many different types of scientists, including psychologists. While this study examined fruit flies, it implies that similar mechanisms may be affecting our behavior, as we may shift our moods from hungry to horny. It will be no surprise if these switches are found, and it may prove the old adage true: “The way to a man’s heart is through his stomach.”
Kenna Castleberry is a staff writer at the Debrief and the Science Communicator at JILA (a partnership between the University of Colorado Boulder and NIST). She focuses on deep tech, the metaverse, and quantum technology. You can find more of her work at her website: https://kennacastleberry.com/