On the wings of love: fruit fly sex, examined

Humans are capable of making rational decisions, but not all the time. Like when you decide to go home with that stranger at the bar instead of calling it a night? When it comes to mating, fruit flies also demonstrate the ability of making rational choices, even if human can’t always.

Researchers at the University of Washington found that male fruit flies displayed a key component of making rational choices through running multiple behavioural experiments. This component is as known as transitivity, where male flies create a hierarchy of preferences and then makes decisions based on that hierarchy.

According to Dr. Devin Arbuthnott, the leader on the project and a current UBC postdoctoral researcher, the scientists marked female flies with red or yellow fluorescent powder. This allowed the researcher to see which fly the male decided to mate with.

After continuing these experiments 10 to 20 times, the researchers discovered that one type of male fruit fly (wild type) called Canton-S, displayed a consistent preference regarding to which female they decided to mate with.

When in close proximity, fruit flies can taste each other’s secretions, which experts believe they use to learn information about a potential mate. Yes, the fruit fly version of foreplay is licking each other. Even male flies with impaired senses of either sight or smell were still able to consistently select female mates they preferred. However, when both sight and sense of smell were impaired, the mating rate dropped dramatically.

In addition, the scientists discovered the females from lines less likely to be chosen for mating secreted higher levels of two particular CHCs (a secretion of chemicals), which may act as “repellent” signals. The scientists counted the number of offspring produced by females from each strain, and found that there was a correlation between males being more likely to mate with females that had a greater capacity to produce the next generation.

So what does this mean?  

Since male fruit flies are able to pick partners who will produce the most desirable offspring, it shows how flies are capable of making rational mating choices.

While it is still unclear what female characteristics are driving their choices, the researchers believe the males used a combination of visual, chemical and behavioural cues from the females to construct this hierarchy of preferences. Who knew fruit flies were so picky?