Pheromones are chemicals that are emitted by animals to mediate bonding behaviors and a new class of pheromones was discovered recently in fruit flies. Pheromones have been studied in many types of animals, including humans, and they have been shown to mediate attraction for mating, bonding behaviors between mothers and their offspring and other behaviors and physiological phenomena. Pheromones are emitted by an animal and these chemicals become airborne. When they are breathed in through the nose (the olfactory system), they attach to receptors in the top of the nasal cavity, and then signals are transmitted to the brain for processing information about, for example, whether a potential mate is nearby and receptive for mating.
In a study published in eLife, fruit flies, properly called Drosophila, were shown to produce a class of pheromones called triacyglycerides. Drosophila triacyglycerides are sex-specific, in this case meaning they were pheromones found in males. Thirteen different versions of triaclyglycerides are secreted by the ejaculatory bulb in males and then the triclyglycerides are transferred to females during mating. Male fruit fly courtship consists of stereotyped, observable features. Wing vibration (called “singing”), foreleg tapping, and proboscis extension are followed by copulaton and deposition of the pheromone. It is thought that the diversification in the chemicals used as pheromones may be related to their diet of fermenting cacti.
These Drosophila pheromones were also found to inhibit courtship from other males. The pheromones that are deposited on the female have anti-aphrodisiac qualities such that the females become less attractive to other males. In the experiments, male fruit flies were given a choice to “court” either a virgin female fruit fly or a recently-mated female. The males were significantly more attracted to the virgin females. In short, the study showed that the pheromones are used to manipulate the post-mating attractiveness of females as well as to get the females to mate.
Bombykol was the first pheromone that was identified and it was discovered in 1959. Bombykol is carried by female silk worm moths and only a few molecules of bombykol emitted into the air by the female can attract a male from as far away as 3 kilometers. The study of pheromones was slow in the beginning but many studies on pheromones have been carried out since the 1970s largely due to the development of sensitive assays for these types of chemicals. Pheromones have been shown to mediate mating behavior in dogs, hamsters and even turtles. Pheromones have also been shown to be the attractant chemical for newborn mice pups to find their mothers to feed. When the mouse mother is lactating, she emits the pheromone which attracts the pups; when the mother stops lactating, she no longer emits the pheromone.
The study of pheromones in humans has been developing for decades but discovery of the actual chemical has been elusive. Considering how confused many people seem to be regarding mating behavior (many famous politicians come to mind but will not be named) it is probably a good thing that the actual pheromone chemical related to human attractiveness has not been discovered yet.
This new class of pheromones that was discovered in fruit flies is just the latest development in the interesting story of pheromones and mating behavior. These airborne chemicals that get captured in a potential mate and produce sexual attraction are small and invisible to the eye but clearly pack a big punch in making sure that there is continuation of the species.
By Margaret Lutze