In this paper recently published in Science, a group from Leuven, Belgium report on insect pheromones. In this study, they have found that a class of pheromones that queens produce are surprisingly similar across a diverse set of social insects. What interests me is not so much the evolutionary ramifications that are the subject of the paper, but rather that the chemical compounds used for signaling are saturated hydrocarbons.
Most signaling molecules in biology – whether its neurotransmitters, hormones, or something else – have much more complex chemical structures. The presence of nitrogen, oxygen, and phosphorus atoms in numerous functional group arrangements allow all kinds of intermolecular interactions such as hydrogen bonding and polar interactions. These tend to be the key to both a strong interaction and specific one. A ligand will bind tightly to its intended target, but not to others and a certain target will bind its intended ligand and not other ones.
But when it comes to hydrocarbons, which contain only carbon and hydrogen atoms, you don’t have as many opportunities for selectivity. Size and shape are essentially the only properties to work with. That is simply not enough for the biochemistry of most organisms. But insects have found a way to make it work.