The other day I read an interesting paper about the identification of a pheromone produced by the Lassius Niger ant queen that promotes worker sterility. A pheromone for those who don’t know is a chemical released by an organism into its environment that facilitates communication with other members of its own species. Humans are thought to have sex pheromones, but due to our advanced speech, eyesight, etc. (things that facilitate communication) we really don’t need other pheromones. Ants however rely on pheromones for the majority of their communication. If you haven’t read my blog before I will mention that ants are eusocial organism that are very community-oriented and behave as a group instead of as individuals. A key characteristic of eusociality is that there is a division of brood care into reproductive and non-reproductive groups.

The main reason organisms reproduce is to pass on their genes to future generations. So then how is there only one queen in an ant colony, one reproducing female? The main evolutionary system at play is genetics, but the way this system is facilitated is through pheromones. What I mean by this is that all ant workers are female and share 75% of their DNA (this is the genetics part) and that makes them okay with only their queen reproducing because they are so highly related that even though they themselves aren’t reproducing, still a sufficient amount of their genes are getting passed onto the next generation. But how does this actually happen? All female ants have working reproductive structures, so why don’t they just reproduce on their own if they feel like it? Well, scientists have found that pheromones are produced by the queen ant that make the female worker ants physically unable to reproduce.

The queens produce a pheromone which is then picked up by the antennae of the worker. The presence of this pheromone causes the antennae of the ants to pass along a signal to the body’s endocrine system. (Sort of similar example in humans: Our body temperature has to stay within a set range for use to stay alive. So when it is cold, the body naturally senses it and reacts; it’s involuntary that blood leaves our extremities and we start to shiver.) It’s kind of the same with ants. The antennae sense the pheromone and through the activity of hormonal pathways, there are signals that cause the ant to be sterile. The sterility is specifically caused by the production of juvenile hormone that inactivates the ovaries. Therefore the ant may have the reproductive structures, but she does not have the proper reproductive hormones and therefore cannot reproduce.

A really interesting thing about this queen control is that it not only affects the reproductive hormone pathways, the study also showed that it decreased worker aggression. This helps prevent a random ant worker from trying to overthrow the queen. The study also showed that when a queen was hurt and an immune response was required, the production of the pheromone was greatly reduced. This mechanism is put into place so that if a queen ant is hurt badly enough that it is affecting her reproductive abilities, the drop in pheromone production will be a signal that the worker ants pick up and it will cause their own ovaries to start becoming active. Then there is sort of a queen race where the worker ant with the highest ovary activation will start producing the queen control pheromones and replace the injured queen. This mechanism ensures the best, most successful reproduction possible, because without it, the colony would collapse.

So I know the part about the 75% DNA may be a little confusing since I did not explain it, but here is a link to a website that explains it well. http://www.bumblebee.org/Haplodiploidy.htm