Parasitic tapeworms manipulate the behavior of many ant colonies

Behavior and lifetime are also affected by tapeworms in non-infected ants
Tapeworms have developed unique strategies to ensure the survival of their species. It has been known for some time that they control the behavior of the affected hosts. Scientists at Johannes Gutenberg University Mainz (JGU) have now found out in experiments on ants that tapeworms also influence the behavior and lifespan of non-infected conspecifics in an ant colony.

According to the results of the Mainz researchers, tapeworms of the genus Anomotaenia brevis can manipulate the behavior of whole ant colony in their own sense. The "aggression behavior of the entire ant colony is decreasing" and the "lifespan of uninjured ants is declining", according to the JGU. Thanks to the lower overall aggression, the infected ants are not removed from the colony and the longer lifespan of the diseased animals increases the chances of survival for the tapeworm in their interior - until the infected animals are finally consumed by a woodpecker, which is the main host for Anomotaenia brevis. The researchers published their findings in the renowned journal "Proceedings of the Royal Society B"..

The tapeworm infection is already externally recognizable in ants. The parasites also cause extensive behavioral changes throughout the colony. (Photo: Susanne Foitzik / Johannes Gutenberg University Mainz)

Externally detectable tapeworm infection of the ants
The data of the research team around the evolutionary biologist Prof. Dr. med. According to Susanne Foitzik, ants are relatively often attacked by parasites, with tapeworms of the genus Anomotaenia brevis using the ants as an intermediate host to complete part of their development before completing their life cycle in the main woodpecker (woodpecker). The scientists investigated the effects of tapeworm infection in the ant species Temnothorax nylanderi, which is native to Western Europe and lives here preferably in acorns or deadwood on the forest floor. The workers of this ant species are two to three millimeters in size and form colonies with 50 to 200 animals. The tapeworm Anomotaenia brevis attacks the animals in the larval stage and settles in their intestines. The infection of the ants is already externally recognizable. Infected animals are yellow and thus differ significantly from the otherwise predominantly brown conspecifics, according to the JGU.

Reduced aggression in ant colonies with infested animals
The tapeworm infection also causes behavioral changes in the affected ants. They are inactive and stay in the nest, where they hardly participate in social tasks such as brood care, the researchers report. However, this parasitisation "not only changed the appearance and behavior of the ants directly affected, but also caused behavioral changes in non-infected nestmates," the researchers write. Thus, the aggressive behavior of an ant colony had decreased markedly when parasitized animals were present in the nest. This has the consequence that the sick animals are not removed from the other ants from the colony. The background for this observation probably forms the chemical signature of the infected animals, which emit a different odor. The nest-specific odor usually forms an identifying feature for ants in group members. "If it is disturbed by other fragrances, this also influences the preparedness against intruders," according to the JGU release.

Reduced lifespan of healthy ants
In addition, the average lifespan of uninfected animals dropped significantly, the researchers report. The healthy nestmates showed a much shorter lifespan compared to other ants from uninfected colonies, not only compared to the infected animals. "The longer lifespan may be a result of altered gene regulation, or perhaps a result of better feeding that infected animals enjoy," says lead author of the study, Sara Beros. The "stress of having to care for the infected animals while at the same time having to give up their labor because they are not involved in community work" may also play a role here.

Altered escape behavior of infected ants
"The parasites have developed fascinating strategies to pursue their own interests and, for example, to multiply better", stresses Prof. Dr. med. Susanne Foitzik. The tapeworms try to "influence the ants so that the probability of being eaten by a woodpecker increases," explains the evolutionary biologist. This is also shown by the reactions of the infected ants to a simulated woodpecker attack. According to the researchers, the diseased animals had a significantly lower escape behavior, which increases the chance for the parasite to be eaten by a woodpecker. In the woodpecker, the tapeworm can finally complete its life cycle. Of the ant colonies in the Lennebergwald, a 700 hectare forest area northwest of Mainz, according to the researchers about one third of all ant nests are affected by the tapeworm Anomotaenia brevis and about 13 percent of the animals are infected. The tapeworms thus have a significant influence on the social behavior and the lifetime of the total population. (Fp)