Shortcuts to power through deception are familiar to human history, from seed intrigues to wars for the throne. In nature, however, this phenomenon is rare. Even so, a team of researchers from Kyushu University in Japan documented a peculiar case in a community of ants. The study, which will be published this Monday in the journal Current biologyreveals a new form of social manipulation: a parasitic queen, a stranger to the nest, triggers matricide by inducing the workers to tear their own mother into pieces and accept the stranger as the new sovereign.
According to the authors, the intruder achieves this by using a strong-smelling chemical compound that is sprayed on the resident queen. This process can be repeated approximately 15 times during the first 20 hours after the initial spray. Once this compound has been impregnated, the operators stop recognizing it as a mother and perceive it as a threat. The result is a ferocious attack that ends in his death after a few days.
Japanese biologist Keizo Takasuka, lead author of the study, explains that the fluid sprayed by the parasitic queen contains formic acid. Explain that the species involved (newly mated queens of Lasius orientalis AND L. umbratus) use this compound as a defense mechanism and to attack predators and prey. “My hypothesis is that formic acid is responsible for the matricide,” he comments.
Biological mechanism
This acid is stored in a poisonous gland. When sprayed, its effect is immediate and operators sense something bad in the mother. “The queen changes abruptly for her daughters and they feel they have to kill her,” explains Takasuka.
This is an extreme case of chemical interference in the signals that hold the nest together: once inside, the intruder carefully approaches the resident queen and, within seconds, sprays her several times with fluid expelled from the abdomen, specifically from the acidopore, a hole-shaped structure. Only with this stimulus are the olfactory signals that maintain social order inside the nest interrupted.
For biologist Sílvia Abril, professor of Zoology at the University of Girona and expert who did not participate in the research, although this is an exceptional case, this is consistent with the nature of these insects. Spending much of their life underground, communication between ants is primarily chemical: “Their entire social structure is in darkness, so their communication is primarily chemical.”
Workers detect whether an individual is an ally or an enemy through their senses. The expert believes that the finding reveals a direct interference in this recognition mechanism. “They are probably manipulating the communication system between the workers and the queens, so that the workers can no longer identify that individual as their queen or their mother,” he explains. “They interpret her as an enemy and that’s why they attack her, without knowing that they are eliminating their queen.”
A matricide never seen before
After the death of the original queen, the intruder takes her place. The workers, orphaned and disoriented by the chemical change, accept the parasite as if it were their own mother and begin to care for her, her and her offspring. The parasitic ant receives care, lays eggs and raises a new colony with them.
Abril points out that what is really striking about the study is that the parasitic queen does not directly kill the nest queen, as is usually the case. “Normally, parasitic queens that enter a colony to take over eliminate the queen themselves,” he points out. “The fact that they manipulate the nest workers so that they are the ones who execute the queen seems very surprising to me and is what I would like to highlight most in this study.”
The specialist also believes that this type of manipulation may not be an isolated case. The difficulty of recording these behaviors within nests means that many episodes go unnoticed. “I think it could happen more often,” he says. “Maybe over the years we will find more similar cases, because manipulation of ant behavior is not that rare,” says the biologist.
Duel of queens
There are precedents within the same species, as in the case of the fire ant, in which queens manipulate workers to eliminate other rival queens. In these cases, explains Abril, these are colonies with multiple queens in which internal competition can trigger pheromone-induced executions. “Manipulation through chemicals is not that great in the ant world,” says Abril. “What is exceptional about this case is that it occurs in the world of social parasitism,” he says.
According to the study, matricide is a rare behavior in nature. On the contrary, the importance of maternal care is paramount and killing the mother is not beneficial. The documented cases, which are limited, concern terrestrial invertebrates and follow two patterns: voluntary matriphagy, in which the mother offers her own body as food to her young; and worker-induced matricide, as in the case of hornets and wasps, when producing males may be more beneficial to workers than keeping the queen alive.
In the world of ants there are also situations in which the elimination of queens occurs without the intervention of parasites. As in the regulation of the number of queens in colonies founded by multiple females – a process known as pleometrosis – in which young queens compete with each other.
For Abril, the fact that formic acid, a compound intended for defense, has evolved to become a mechanism capable of altering social recognition “is a very interesting change on an evolutionary level”. But it leaves a great unknown: explaining what made it possible.
