Do Ants Fight Smart ?
The Slave-Maker ant is a social parasite. No, it isn’t a pest to humans but it shows brood parasitism with other species of ants, quite like the cuckoo.
It raids the nest of other ants and steals their pupae. Once the pupae hatch, they are made to work as slaves! The slave-making ant speciecs Protomagnathus americanus prefers to raid the colonies of Temnothorax longsipinous .They do so by sending a scout to find a suitable target and then sending a raiding party to enslave the Temnothorax. The raiding party include both slavemakers and enslaved Temnothorax of other nests.
Scientists at the LMU university conducted a very interesting experiment to see if the host Temnothorax really do fight smart. Do they exhibit aggression on different levels when dealing with slavemakers , or is it a constant level irrespective of the opponent ? If yes, what determines high levels of aggression ? Also, how long do the aggressive levels last ?
In the experiment, the scientists subjected the nests of the Temnothorax to three sets of treatments. Each treatments involved keeping a dead ant ( dead, to avoid aggression caused by the ant’s behaviour ) and seeing the response.
Treatment 1 involved introducing a non-nestmate Temnothorax worker , followed by a slave maker three days later , so that the ants would think it was a scout and then again after 3 days, a non-nestmate Temnothorax worker. This was to make them think it was a member of the raiding party .In treatment 2, instead of Temnothorax worker after the slavemaker, another slavemaker was introduced as a member of the raiding party.
In both cases , the aggression( found out by the amount of biting, holding, stinging etc) towards the initial Temnothorax worker wasn’t much. But, towards the slavemakers and the “raiding” workers, they showed a much higher level of aggression.
Killing a slavemaker was nearly always beneficial as the scout couldn’t “report back “ or the raiders could be stopped . This could explain the higher level of aggression.However, the response to non-nestmate Temnothorax workers is context dependent. A host colony has about 50% probability of being attacked in a year. This probably explains the drastic change of behaviour in response to non-nestmate workers.
Treatment 3 aimed to find if the aggression was based on how chemically different the slavemaker was from the host. So, the scientists introduced Temnothorax curvispinous, a species phylogenetically closer to the hosts than the slavemakers but more chemically distant than the slavemakers. Here, the aggression level wasn’t much. So, this meant the aggression was more slavemaker targeted.
We still hadn’t got the answer to how long the aggression lasts. To treatments 1 &2 , another non-nestmate worker was introduced after 14 days and a low aggression level was recorded , indicating that the aggression would fade in two weeks.
This was a very elaborate and hugely successful experiments but , it isn’t devoid of its flaws. It used dead ants. But there could be a possibility that the behaviour of the invader could produce a response in the hosts. This can be easily checked by replacing the dead ants with live ones and checking the differences.
Also, the environment selected has no (or little) competition between the nests of two host colonies. Increased competition for resources, might cause the hosts to attack all non-nestmates to reduce the competition.
Furthermore, if the resources are scarce, the cost of aggression, that is , the lack of time spent in foraging of food , might be high and the hosts might prefer not to attack. Here, experiments can conducted using game theory principles, to find out the tipping point.
Aggression can also be season specific because slavemakers never go out on raids in spring. Some colonies show a higher level of aggression than others, indicating environmental factors at play.
There are many such experiments we can try to know more and it can be quite fascinating to see nature evolve mechanisms of intricate strategy.
