UCR fruit fly study’s findings could help explain human behavior

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UCR researchers are exploring how experiencing rejection can influence future courtship behavior. The focus of this study was on behavioral patterns of male fruit flies before and after experiencing rejection from females. The experiments were led by Michael Adams, a professor of entomology and neuroscience, who was joined by UCR graduate students Sang Soo Lee, Yike Ding and Natalie Karapetians. Crisalejandra Rivera-Perez and Fernando Gabriel Noriega from the Florida International University, Miami also assisted in the study.

When asked why fruit flies were chosen for this experiment, Lee responded, “Fruit flies were the best model for gene expression.” As a matter of fact, fruit flies share around 80 percent of human genes; this and their short life cycle made them ideal for this experiment, according to Lee. Said flies were then placed in a tiny apparatus, where those observing could unite and isolate them with ease.

The experiment begins with a male fruit fly and a recently paired female; because she has already mated, she constantly rejects the male’s advances. Afterward, the two are separated and the male is placed with a virgin female who should be open to his advances. However, rather than courting with this female, the previously-rejected male shows little to no interest. To make sure that the virgin female is not the problem, a different male is brought in and proceeds to court with her as usual. This experiment proves that the previous experience impacted the rejected male, causing him to lose interest in mating. “It’s very depression-like behavior,” said Lee. “It’s very similar to when we as humans are rejected by a woman. After rejection, we drink, we distract ourselves, and we try to convince ourselves that we don’t want a woman,” explained Lee.

When asked for their thoughts on this study, students gave a variety of answers. “Well to me this study seems like an interesting way to analyze animal behavior,” says Rohan Kamath, a second-year Cell, Molecular and Developmental Biology major, “I’m interested in seeing how the lab could possibly use a different organism as a new model and how it could eventually be applied to humans.” Sattia Oum, a second-year Business major, also gave her thoughts on the topic. “I just think it’s really sad,” Oum stated. “The fact that a negative experience can have that big of an impact on an animal’s behavior. Flies have never been my favorite animal, but I can’t help but feel sorry for them.”

The explanation for this behavior, according to the study, is hormones. Ecdysis triggering hormone (ETH) is an essential hormone for forming memories in these fruit flies. In the experiments, when ETH was silenced the previously rejected male would continue to show interested in females. This is because without ETH, the memories of rejection cannot be formed.

The study raises questions about its implications for humans. But according to Sang Soo Lee, things are not that simple. “What this study does is help identify the building blocks for emotions,” he says. “Compared to fruit flies, humans are much more complex. What this study does is set a foundation that future studies can later build on and eventually apply to other animals, including mammals.”

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