Worth the effort?
It may make sense to feed the children of a close relative - after all, a few of your own genes also benefit from it. However, the family relationships cannot explain why some animals in an insect colony sacrifice themselves more and others less for the queen's offspring. Should cool calculation matter instead?
For the queen there is only one thing in life: produce offspring. She is not interested in anything else, she even leaves the raising and care of her children to her numerous servants. They willingly take on these tasks, diligently go out in search of food and lovingly nurture and care for the little ones. They even go so far as to do without their own offspring completely in favor of the boss. However, not all wasps exert themselves equally in their work. Some work tirelessly, while others shy away from work whenever they can. Why is that?
Scientists initially tried to justify this phenomenon with the degree of kinship: The more closely the animals are related to the offspring they are raising, the greater their commitment - after all, they are supporting the continued existence of part of their own genes. Conversely, the lower the degree of kinship, the less similar the genes are - so the amount of work is not particularly worthwhile. Distant relatives should therefore pursue their leisure time rather than caring for foreign offspring.
However, this theory does not stand up to scrutiny in the insect colony: only ten percent of the variation in the helpfulness of the workers can be explained with it. Jeremy Field, Adam Cronin and Catherine Bridge of University College London tested just another hypothesis. They suspected that the animals calculated how much it would cost them to help the queen in terms of their own lives, and then invested more or less in the work based on the cost-benefit ratio.
The London entomologists tested the hypothesis on the wasp species Liostenogaster flavolineata, which lives in small colonies of a maximum of ten animals in the tropical rainforest. A single female, which looks no different from the others, lays all the eggs. The other wasps feed the offspring and wait patiently for the moment when they get the chance to lay their own eggs. Succession to the throne is strictly based on age: the oldest female takes the place of the queen if she dies. The insects stand in line, sorted by age, and wait for their chance to reproduce.
Field and his colleagues hypothesized that the oldest wasps, who are at the front of the queue, should put less effort into the alien offspring, since they ultimately have a better chance of having offspring of their own than younger specimens. At the same time, their chances of living longer are better because the queen lives significantly longer than her subjects. A certain laziness would be doubly advantageous for older animals. Younger wasps, on the other hand, have little hope of ever becoming queens, so feel free to invest their energy in the offspring.
The scientists now marked the wasps according to their age and observed the diligence of the individual specimens. As expected, the younger insects were out and about much more often than the older ones to fetch food for the little ones, whereby the degree of relationship of the individual insects to the queen had no influence on their diligence.
Now the biologists messed up the line of succession by removing the colony's second-oldest animal. As a result, the wasp, which was in third place, moved up and took the place of the missing insect. Immediately, the advancing animal drastically reduced the number of its excursions according to its now higher rank. It had evidently recognized that its chances of having its own offspring had increased and had adjusted the amount of work accordingly.
In a second part of the experiment, the researchers eliminated all animals from the colony except for the queen and the highest-ranking wasp. Suddenly the second in rank worked hard and intensified her brood care, but no longer worked as the second in rank from states that consisted of only two wasps to begin with. The insects therefore knew very well that if they took over the place of the queen, they would have no helpers for their own offspring and therefore made more effort for the foreign offspring.
At least the wasp species Liostenogaster flavolineata seems to make a kind of cost-benefit calculation and adjust the amount of work they have to do for foreign offspring to the chances of having their own offspring.