Pheromones, And How Ants Find Their Way Home
Chris - When women live in the same house, such as with groups of students, they often find their menstrual cycles start to synchronise. Why is this?
Graeme - We don't know for sure, but it might be a chemical from under the arms that can influence menstrual cycles. An experiment was carried out where chemicals from a woman in the early stage of her cycle were put on the upper lips of other women. This caused the other women's cycles to shorten. When the same experiment was performed using chemicals from a woman late in her cycle, the cycles of the women in the experiment seemed to lengthen.
Chris - Why would it be advantageous for women to have their periods at the same time?
Graeme - That's a good question but no-one really knows. If females were all to come and be receptive at one time, then it would mean that males are more likely to pair up with individual females and there'd be less likelihood of males having more than one female partner. Alternatively, it could have something to do with the possible rearing of the offspring. This is very difficult to see in terms of human biology. No-one really knows.
Chris - Part of your work is on social structure in insects and how chemicals like pheromones can change how different insects behave. Ants are a classic example of this.
Graeme - Yes they are. When you look inside an ant colony, you can see the queen and the ant workers. The workers are divided into castes: you might have foragers that go out and find food and you might have nurse ants that stay at home and look after the young. One of the things we can do is distinguish between the queen and the different types of workers by their chemicals.
The chemicals themselves don't make ants do different jobs. The roles each ant performs in the colony seems to depend on how old you are. Those that go outside the colony are going to be mature individuals. As workers are expensive to make, you want to get as much work out of them as possible. When they are young, it's best to give them jobs inside the colony and keep them safe. Only when they are older and more dispensable does it make more sense to send them out.
Lots of work has been done on bees. In a social insect colony, it's basically just a lot of women living together. The queen produces a chemical that controls the reproduction of all the other individuals by turning off their ovaries.
Chris - Are there analogous genes in people?
Graeme - No. It's a totally different social structure. Social insects are very specialised.
Chris - When you find an ant in your house, do you kill it or study it?
Graeme - I tend to study it, although it's not good if you find ants in your house.
Kat - Can you get rid of ant trails altogether so they stop coming in your house?
Graeme - No, not really. When an ant finds some food, it leads a chemical trail back to the nest for others to follow. While there's food there, the ants will keep on reinforcing the trail. Therefore it's very hard to get rid of them once they're there. The trails remain.
If you took the back end of a few ants and made a trail to send them back outside, you might end up getting rid of them! The trails are just made in chemical glands in back of the ant. As it drags its bottom along the floor, the compounds are released. Sometimes have a sting which almost acts like a nib. Once on surface, the compounds start to evaporate into the air. The antennae can then pick up these signals. Antennae are like ant noses.
Chris - How do they know which way is home?
Graeme - It's all about the angles at which the trails are being laid. When you leave the colony, you probably walk for a bit and then split off into two directions. Whenever they split, they choose an angle, usually about 51 degrees. This means that when the ants are walking away from home, they always find angles at 51 degrees. When walking back the other way, the angle is completely different. This allows them to know which way they're going.