Headless mating flies and how we tell time
This may sound familiar: you are studying and your phone buzzes. At first, it is easy to stay focused, but as more time passes, it becomes much harder to ignore the distractions that surround you. The conflict between persisting in one task and moving onto another underlies much of our behavior. Our ability to maintain a behavior or a state of mind over time is affected by our internal state (our emotions and our mindfulness), the external environment, and the interplay between the two. What are the mechanisms that are controlling our task persistence?
A recent study by Michael Crickmore and Leslie Vosshall at the Rockefeller University gave us clues into this problem. The researchers studied the duration of copulation in Drosophila melanogaster as a model system for the coding of time and persistence. Fruit flies typically mate for around 30 minutes, with little variation in copulation times within the species. In the article published in Cell, the researchers investigated the duration of copulation as it is determined by the persistence of the male fly. At the beginning of mating, the flies are very persistent and will ignore minor disruptions in their environment. As the mating continues, the flies become less persistent and more likely to respond to distractions.
The researchers found that the duration of copulation was controlled by two opposing neuronal populations, which are independent of the transfer of reproductive fluid. The persistence in mating was controlled by a set of neurons that motivate behavior, in this case, successful copulation. The decline in persistence was promoted by a separate population of neurons that contribute to an overall decline of persistence over time as the probability of successful mating increases, as well as integrate information from the external environment to influence the duration of copulation. These neurons work in opposition to each other, as the persistence will decline until other goals are able to cause the end of copulation and a change in behavior.
The neurons that contribute to an overall decline of persistence over time were shown to release GABA, an inhibitory neurotransmitter. These GABAergic neurons play an important role in the cost-benefit analysis of the behavior duration. They contribute to an overall decline of persistence over time as the probability of successful mating increases, as well as integrate information from the external environment to influence the duration of copulation. In ideal mating conditions, these neurons cause persistence to decline through GABA release on a timescale that ensures the success of the copulation, and in adverse conditions, such as intense heat or forceful wind, integrate the external information to influence the decision to prematurely end copulation or not. The longer copulation had progressed, the more likely an adverse disruption would end copulation, suggesting that persistence is decreased by these neurons until other internal or external drives are able to change the behavior of the fly.
The GABAergic neurons work in opposition with dopaminergic neurons, which motivate the mating behavior, to control the duration of copulation in Drosophila in a system that is so significant that duration has little variation across the species. This system is simple and powerful, which not only makes it an ideal system to study the neuronal basis for persistence and motivation, but is promising as a model for further study of interval timing mechanisms and the neural coding of time in animals.