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Many insects release chemical signals, known as sex pheromones, to attract mates over long distances. The pheromones of male bumble bees, for example, contain chemicals called fatty alcohols. Each species of bumble bee releases a different blend of these chemicals, and even species that are closely related may produce very different ‘cocktails’ of pheromones.
The enzymes that make fatty alcohols are called fatty acyl reductases (or FARs for short). Any change to a gene that encodes one of these enzymes could change the final mix of pheromones produced. This in turn could have far-reaching effects for the insect, and in particular its mating success. Over time, these changes could even result in new species. Yet no one has previously looked into how the genes for FAR enzymes have evolved in bumble bees, or how these genes might have shaped the evolution of this important group of insects.
Tupec, Buček et al. set out to learn what genetic changes led the males of three common species of bumble bees to make dramatically different mixes of pheromones. Comparing the genetic information of bumble bees with that of other insects showed that the bumble bees and their close relatives, stingless bees, often had extra copies of genes for certain FAR enzymes. Inserting some of these genes into yeast cells caused the yeast to make the correct blend of bumble bee pheromones, confirming that these genes did indeed produce the mixture of chemicals in these signals.
Further, detailed analysis of the bumble bees’ genetic information revealed many genetic sequences, called transposable elements, close to the genes for the FAR enzymes. Transposable elements make the genetic material less stable; they can be ‘cut’ or ‘copied and pasted’ in multiple locations and often cause other genes to be duplicated or lost. Tupec et al. concluded that these transposable elements led to a dramatic increase in the number of genes for FAR enzymes in a common ancestor of bumble bees and stingless bees, ultimately allowing a new pheromone ‘language’ to evolve in these insects.
These results add to our understanding of the chemical and genetic events that influence what chemicals insects use to communicate with each other. Tupec, Buček et al. also hope that a better knowledge of the enzymes that insects use to make pheromones could have wide applications. Other insects – including pest moths – use a similar mixture of fatty alcohols as pheromones. Artificially produced enzymes, such as FAR enzymes, could thus be used to mass-produce pheromones that may control insect pests.