Flies, too, are affected by peer pressure, say U of T Mississauga researchers
Post-doctoral fellow, graduate student make research breakthroughs
By Olena Wawryshyn
The power of peer pressure is well known to be mighty. But, even the tiny fruit fly is affected by its social group, according to two new studies conducted by University of Toronto Mississauga researchers.
The studies, published on Sept. 11 in the journal Current Biology, reveal that the social environment of flies can change their physiology, gene activity and behaviour, including mating patterns.
"Many take for granted that communication among insects is hard-wired, but we have shown that communication is influenced by social relationships even in insects like fruit flies, which have not been traditionally considered to be social insects," said Professor Joel Levine of the Department of Biology at U of T Mississauga, senior author of the studies. "We have seen that individual responses are altered quickly--within a day of joining a group. This level of spontaneity or plasticity is complex because it occurs on many levels: involving neural and non-neural tissues, changes in gene expression and physiology and changes in behavior, all of which are inter-related."
Their approach in examining individual flies within their social environments fills a gap that is missing in other experiments that focus exclusively on either individuals or their environments.
In one of the University of Toronto Mississauga studies, Levine and his research team discovered that specialized cells of the fly called oenocytes, which produce chemical communication signals known as pheromones, operate according to an internal circadian clock. The clock's "ticking" varies depending on the flies' social group. They found that males in mixed groups--where the flies were less like each other at the genetic level--produced different chemical signals than those in more uniform groups.
Moreover, the composition of the group had a clear effect on sexual behaviour: flies in mixed social groups composed of different fly strains had more sex than those in homogeneous groups (where flies were more similar at a genetic level).
The second study further explores the connection between chemical communication among fruit flies and their physical and social environments by examining the blend of pheromones produced by flies in mixed versus homogeneous groups.
"The response of an individual male to others with similar genes depends on his neighbors," Levine said. "That response is quite specific because it affects some of the chemicals involved in communication, but not others." The results suggest that chemical communication is a "fickle" trait that depends heavily on the influence of a fly's peers.
The findings also challenge the traditional view of the relationship between behaviour and the underlying mechanisms that control that behaviour, Levine noted. "Membership in the same social group trumps genotype as a predictor of chemical displays," he said. "At a general level, the surprise comes from appreciating that molecular function is altered by behaviour. Behaviour is not only the product of molecular mechanisms, it is also a player in those mechanisms."
These new discoveries were made possible through an innovative method of dissecting flies, developed by a U of T Mississauga post-doctoral student, Joshua Krupp, who is the lead author of one of the two studies. "He figured out a way to open the fly and cut the muscle away from the oenocytes so that these cells could be isolated and studied," said Levine. "The ability to study the flies in this very specific way helps us understand the cellular control of chemical signalling." The dissection was a key technical breakthrough.
Similarly, the computational analyses that biology graduate student Clement Kent contributed were critical. Kent, who is the lead author of the second paper made several innovative contributions. "He developed new tools for the analysis of chemical signals. In addition, he found ways to analyze relationships between the flies by a novel application of a theory from the field of evolutionary biology." One of these revealed insights into the influence of peers on a male's chemical signalling.
Other researchers on the team included Jean-Christophe Billeter, who is conducting post-doctoral research in Levine's laboratory; Christophe Lucas, Benjamin Smith and Anthony So, who were also post-doctoral researchers when the studies were undertaken; and biology lab technicians Reza Azanchi and Julia Schonfeld.
"A lot of work went into these two studies - thousands of samples were taken, and the analysis of the chemicals is very labour-intensive," said Levine. "It was a team effort."
Funding for the research was provided by the Canadian Institutes of Health Research (CIHR) and the Canada Research Chair program.