When Professor Joel Levine's team
genetically tweaked fruit flies so that they didn't produce certain
pheromones, they triggered a sexual tsunami in their University of
Toronto Mississauga laboratory.
In fact, they produced bugs so
irresistible that normal male fruit flies attempted to mate with
pheromone-free males and even females from a different species,
generally a no-no in the fruit fly dating scene.
The study points to a link between sex,
species recognition and a specific chemical mechanism, and is part
of Levine's larger research into the genetic basis of social
behaviour.
"This is important not only from the
point of view of understanding social dynamics, but it's also
fundamental biology, because these pheromones provide recognition
cues that facilitate reproductive behaviour," says Levine, an
assistant professor of biology. "Lacking these chemical signals
(pheromones) eliminated barriers to mating. It turned out that males
of other species were attracted to females who didn't have these
signals, so that seemed to eliminate the species barrier."
In this study, they focused on
recognition—how individual Drosophila melanogaster (fruit flies)
know what their species is and what their sex is. While previous
studies had suggested that pheromones played an important role,
Levine's team decided to genetically eliminate a certain class of
these chemicals, called cuticular hydrocarbon pheromones, to
determine their particular effect.
The researchers found that female flies
bred without the hydrocarbons were melanogaster Marilyn Monroes to
normal males. But the effect didn't stop there—males lacking the
hydrocarbons were also sexually irresistible. In fact, females
lacking the hydrocarbons were so sexy that males of other Drosophila
species courted them.
When the researchers treated females
bred without the hydrocarbons with a female aphrodisiac, it restored
the barrier preventing sex between species, suggesting that a single
compound can provide species identity. "That means the same chemical
signals and genes are underlying not only social behaviour in
groups, like courtship and mating, but also behaviour between
species."
Levine stresses that while pheromones
are part of the human mating dance, the cues for attraction are far
more complex in our species.
"Although I am no expert on human
pheromones, there is evidence that men and women may discriminate
odours from the same sex or other sexes differently, and there's
even some evidence that how an individual discriminates those odours
may reflect their gender preference," he says. "We may rely more on
the visual system, and we may have a more complex way of assessing
other individuals and classifying them and determining how we're
going to relate to them than a fly does.
"But what we're looking at is a spectrum
across biology of a tendency to understand how others relate to
ourselves. It's clearly an issue that humans are caught up in—it's
in our art, like Madame Butterfly and it's in our newspapers, in
terms of sports issues like the recent controversy about the sexual
identify of the South African runner Caster Semenya."
For more information
University of
Toronto
(MDN) |