Results from a Texas A&M University Ph.D. candidate’s study of fruit flies’ behavior patterns suggest that only positive sexual experiences make male fruit flies better at future copulation attempts. The finding is relevant for neural and behavioral biologists in general, but it also may change the way scientists interpret the learning capacities of these animals.
TAMU researcher Sehresh Saleem’s study tested if fruit flies were able to improve their sexual performance through previous learning experiences. “I’ve always wondered, are some flies smarter than others? Better learners?” she asks. “One aspect of this is, are some flies better maters? So, the idea is, if certain males get better from experience, are these particularly fast learners?”
Previous research was conducted on the subject to determine how prior social experience affects future sexual behavior. However, Saleem and her Ph.D. advisor Ginger Carney both believe that focusing primarily on negative social interactions, such as courtship conditioning, may be limited and may miss critical aspects of the behavioral evolution.
“Copulation is important for these males to complete,” Saleem explains. “It results in a positive response in the males. It’s been shown that male fruit flies become less aggressive toward females after mating. It’s the act of mating that causes this change in behavior. Courtship alone doesn’t do it. So, there’s a key aspect of rewarded learning here that we’re not looking at.”
Fruit fly courtship includes fixed rituals, such as the male chasing the female, tapping the female’s abdomen with the forelegs, unilateral wing extension and vibration (which emits a sound called singing), and licking the female. After this sophisticated set of behaviors, the male will try to copulate by bending the abdomen towards the female. If she felt attracted by the courtship, she will allow it.
During the trial, male fruit flies were split in two groups. One of them received a level of sexual experience, which was only courtship of a receptive female but no copulation, while the other received two levels of sexual experience, courtship, and complete copulation. Then the two types of males were placed alone with a new female to record their courtship behavior and pitted the two males to compete in the arena for the female.
Results showed that males who had completed one copulation, when alone with the female, spent less time courting the new partner than the less experienced ones. They also increased the frequency of abdominal bends. Regarding competition, the findings were similar. While the overall courtship duration was similar, the experienced males extended their wings for a longer period of time and more often during the singing phase, however, and tried to copulate more times.
As a result, the experienced males reached copulation significantly more times than the less experienced ones. “In general, the more naïve male is wasting his time doing other behaviors that are not fruitful, such as chasing the female. The experienced male knows what to do. He’s more efficient. There seems to be some degree of strategy,” Saleem explains.
A second phase of the trial was performed by removing the ability of the females to hear, smell, or see the partners, to understand how females chose the male, by painting the eyes of some females and removing the tips of the antennae of others. When males tried to copulate again, researchers analyzed that vision was not important in the choice of the female, since the preference went to the most experienced males as well.
The results weren’t surprising because, according to the scientists, while the males use vision to locate females at long distance, both genders rely on other specialized modalities when nearby. The finding is the opposite, however, when it comes to audition. “The experienced male lost his competitive advantage,” Saleem explains.
Despite the positive results of the study revealing that fruit fly males can learn from positive past copulation and are rewarded from experience, the researchers were not able to determine whether males are better learners.
The study, which was published in PLOS ONE, was presented at the 2014 annual meeting of the Society for Integrative and Comparative Biology in Austin, Texas.