2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
Hairless mole rats (Heterocephalus glaber).
Naked mole rats take over the territories of neighboring colonies, kidnap the cubs and turn them into workers. This is the conclusion reached by researchers who observed the behavior of these rodents in their natural habitat. As noted in an article for the Journal of Zoology, the high level of aggression between colonies may explain why communities of naked mole rats are composed of such a large number of individuals: the more workers in a colony, the higher the chance of repelling an attack from neighbors or expanding their own possessions at the expense of others.
Bizarre naked mole rats (Heterocephalus glaber) are some of the most unusual mammals in the world. They almost do not feel pain, go without oxygen for a long time, rarely get cancer, age slowly and have a record longevity by the standards of rodents. Their social behavior is no less interesting: mole rats are one of the few mammals that have developed eusociality. Colonies of these rodents consist of a breeding pair and several hundred workers who collect food, build tunnels and care for the young. This structure of communities is more typical for ants or termites than for mammals.
Zoologists still have little understanding of why naked mole rats have developed a collective lifestyle. In the past, it was believed that, like social insects, members of the colonies of these rodents are closely related to each other, but more careful research has disproved this idea. Another hypothesis connects the sociality of diggers with life in an arid habitat, where food resources are unevenly distributed. However, this does not explain why their colonies are so large. For comparison, representatives of a related species, Damar sandworms (Fukomys damarensis) live in similar conditions and also lead a social lifestyle, but the number of workers in their collectives rarely exceeds 40 individuals.
A team of experts led by Stan Braude from the University of Washington presented their views on this issue. They noticed that in captivity, naked mole rats distinguish members of their colonies well from strangers and behave extremely aggressively towards the latter. The authors suggested that this behavior could be explained by high competition between individual colonies. In such conditions, small colonies do not have enough resources to defend themselves and disappear under the onslaught of their neighbors.
To test this hypothesis, Braude and his colleagues studied data on the behavior of naked mole rats collected in the Meru National Park (Kenya) in 1990-2005. In the course of this study, zoologists trapped rodents from several colonies and marked them with individual tags, and also performed genetic analysis of individual individuals.
During the study, the authors found excavators four times intruding on the territory of their neighbors. In three cases, the aggressor colonies were more numerous than their victims. Apparently, such conflicts occur more often, but due to the underground lifestyle of excavators, they are hidden from the human eye. Nevertheless, over several years, researchers have recorded how 26 colonies expanded their possessions at the expense of territories taken from neighboring communities. In half of the cases, the victim colony had to make room, and in half it disappeared completely.
Moreover, it was found that naked mole rats not only occupy foreign lands, but also steal young. In May 1994, researchers captured all specimens from the EE colony in order to tag them and conduct genetic analysis. At the same time, they noticed the wounds on the queen's face. A few days later, invaders from the larger neighboring QQ community infiltrated the temporarily deserted tunnel system. The researchers also caught them and kept them in captivity for several days. After completing all the work, the authors returned the diggers to their native colonies.
A year later, when examining the QQ colony, the researchers found two workers who, according to genetic analysis, came from the EE colony. During the work carried out in their home community in the previous year, both of these individuals were calves. Soon after, the colony of EE, apparently, disappeared: over the next ten field seasons, scientists have not been able to find traces of it.
According to the authors, this indicates a tendency of naked mole rats to steal their cubs. Similar behavior was once recorded in captivity (unpublished observation), but has not previously been noted in the wild. The abduction of young and their transformation into workers resembles the behavior that is characteristic of some species of ants that steal eggs and larvae from congeners and representatives of other species.
Conflict between colonies (and the propensity to abduct offspring) may be the main reason why colonies of naked mole rats are so large. Larger communities are more likely to maintain and increase their holdings, which prompted this species to increase the number of workers.
Unfortunately, studying naked mole rats in nature is not easy due to their secrecy and underground lifestyle, and in captivity, colonies are kept in isolation from each other, preventing them from interacting. Nevertheless, the researchers hope that modern technologies for tracking individual individuals will help confirm their assumption.
Naked mole rats have many unusual abilities, but in some respects they are inferior to normal mammals. For example, these rodents are very hard of hearing. Biologists recently explained the mechanism of almost complete deafness in mole rats: it turned out that sound amplification does not occur in their ears due to mutations in proteins that bind the hairs of the auditory receptors.