Naked diggers as biological nonsense
Interview with Olga Averina
Scientists from many countries of the world wonder how small animals naked diggers manage to live for a long time, more than 30 years, because for rodents it is nonspecific. Usually, as an example of longevity, animals are put much larger: turtles, whales and elephants. Olga Averina, a junior researcher at the A.N. Belozersky Research Institute of Physico-Chemical Biology of Lomonosov Moscow State University, told about what kind of long-lived animals they are, in what natural conditions they live and what conditions they have been created in the Moscow laboratory.
What is unique about naked diggers?Naked diggers are very special rodents, their natural habitat in Ethiopia. The conditions there are quite harsh. They have evolutionarily created for themselves a system of living in colonies: "eusocial relationships" in which a female queen and one or two male "husbands" reproduce, and all other individuals stop sexual development at the very beginning of development, and they are all asexual beings for each other, so-called working individuals. They have many stages of social relationships: one of the working individuals has to dig tunnels, someone protects from predators (most often a snake acts as a predator), there are nannies who take care of new litters, and so on. And this eusociality allows them to survive in these harsh conditions. There are suggestions that eusociality also affected their life expectancy. The main feature of the naked digger is that, unlike similar rodents such as mice and rats, naked diggers live for more than 30 years. And we are studying what is their secret of eternal youth.
There is reliable data from laboratory observations that the queen, unless, of course, she is overthrown and she does not die, lives longer than working individuals. But what does it mean to live longer? They almost never die from some internal, natural diseases, they have eusocial relationships, as a result there can be very serious social clashes. It is because of fights that they most often die.
How long have you had these animals? How many were there and how many are there now?
At the moment, we have three fairly large colonies of 30 to 60 animals. Initially, in 2016, we had one colony, which came from our great friends – employees of the Berlin Zoo. Gradually, we also began to try to multiply them. Then two new colonies appeared, which were created from working individuals. If they are isolated, they can begin to develop their "sleeping" sexual system and become able to create their own family. Thus, we have an old colony, which was originally from the Berlin Zoo, and two already new colonies.
Earlier you said that in Ethiopia, diggers live in rather difficult conditions. In what conditions do they live here, in this laboratory? Is it possible to say that they feel at home?
Of course, we strive for this very much, but let's not forget that we are not a zoo, but, after all, a laboratory. Therefore, we must adhere to standards, but we strive to recreate more or less natural conditions for naked diggers. For example, laboratory mice that live in families or in some same-sex groups are kept in cages. Usually we imagine a cage like this: the cage itself, where there is a drinking bowl, a grid, food and some kind of enrichment of the environment. On the contrary, naked diggers are eusocial animals. They cannot be kept alone, or in very small groups. They live as a family. Each member of the "family" is a colony, very important, they perform certain tasks. They can exist exactly together. To do this, they need to create branched mazes, and we have created mazes from plexiglass, in which there are certain compartments and transition corridors. It's very similar to the corridors they have in nature, underground in Ethiopia. There are indeed corridors, separate rooms, and here, in laboratory conditions, we try to recreate similar conditions.
According to the conditions, the content of naked diggers is very different from the content of laboratory mice – in temperature and humidity. We are used to keeping laboratory mice in the region of 22-24 degrees Celsius, but here the temperature regime is higher, it is 27-28 ° C. Humidity should be around 50%. Already from the name we know that the naked digger is devoid of hair, he has only small vibrissae. Humidity is very critical for him, so that the skin does not dry out.
Maintenance is also nutrition. Unlike standard compound feeds, which are absorbed by laboratory rats and mice, we must provide diggers with fresh food – mainly root vegetables such as sweet potatoes, carrots, celery root, this is somewhat similar to their natural diet. We also add, for example, apples. Because, unlike any other laboratory animals, they do not drink pure water, i.e. they get their vital moisture from vegetables and fruits.
Did you come to these conditions of detention of diggers yourself, or did you learn something from your foreign colleagues?
Yes, of course, we have adopted the experience of our foreign colleagues, because diggers appeared at Moscow University only in 2016, and all over the world they are in zoos, there are also in laboratory conditions. We consulted with our friends from the Berlin Zoo. In principle, the literature also describes exactly how to keep naked diggers.
Tell us about the research that is being conducted on them.
The specifics of our research lie in the questions of what exactly allows a naked digger to live so long, and, most importantly, not to age. We have shown that the naked digger is one of the animals that shows signs of neoteny when an adult individual shows signs of newborns, or even signs at the level of embryonic development of a close species. If we compare a rat and a naked digger, then even in its appearance, not to mention the internal molecular and physiological aspects, it really looks very much like a newborn baby rat. The naked digger has no pronounced auricles, no fur, for example, he has underdeveloped lungs. But we "dug" even deeper: we studied mitochondrial respiration, because our laboratory is directly connected with a large project on the study of reactive oxygen species, and, in parallel, Skulachev ions are being studied. We continue these studies, naked diggers are one of their parts. Therefore, for example, we have proved that mitochondrial respiration in a naked digger is similar to that in newborn mice. And many signs of neoteny, which are described in the article by Academician Skulachev in the journal "Physiological Reviews", just say that the naked digger prolonged his life. At some level, he exists as a small rodent, but already in an adult state. That is, its signs at the age of 20, 13 are physiologically similar to those of newborn mice, with which we can compare them.
We also notice a great influence of the eusocial relationship in the colony. It is believed that this also had a great influence on the fact that they can live for a long time and not grow old, because the peculiarity of the naked digger is not even that he does not age for a long time, but that he does not even show signs of senile diseases already in adulthood.
Are these properties only in diggers, or do other animals also have something similar?
There are several centenarians on our planet. We know about the bowhead whale, about the shark, about the turtles, but we noticed that they are all very large objects. Roughly, but in principle, it is believed that the larger the object, the longer it will live. So we can remember the elephant. The uniqueness of a naked digger is that it is a small object. And similar-sized animals, rodents, live ten times smaller. Let me remind you, a mouse is about 3 years old, naked diggers are about 30 years old, although they are similar in size. This is their uniqueness.
There is another animal – small bats. They are also long-livers, they are also studied by gerontologists, trying to understand why this small object can live for a long time. This is also a very interesting object of research.
As far as I understand, a naked digger's life is prolonged due to a long youth. How is it with other long-lived animals?
In a naked digger, all stages of life are rather prolonged. For example, in a mouse pregnancy, embryonic development lasts 21 days, in a naked digger around 71 days. Also about growing up. In a naked digger, since they do not have full sexual development, if they are not isolated and if they do not find a partner in another environment, namely in the family, it is believed that they become adults only by the age of six months, one year old and begin a good, active social life. A mouse already at 4 weeks of age, almost immediately after lactation, at 4-5 weeks can already begin to reproduce and is considered an adult animal. That is, we understand that this is a huge difference between six months-a year and 4-5 weeks. And so all the stages of the naked digger's life are prolonged. If we compare with other animals, then elephants have a very long period of embryonic development, 22 months, as well as childhood and adolescence, but in order to compare with them, they need to be further studied, which is not easy to do in the laboratory.
Do you plan to study other animals in your laboratory, for example, bats, which are also long-lived?
This is a very interesting aspect. Why did scientists get so excited about studying gerontology and aging issues of naked diggers, why did they take this particular object? Because there is still a question of content. A naked digger is still a rodent, and we have an object with which it can be compared. We, the scientific community, have had standard laboratory rodents since the beginning of the XX century. We brought out a standard laboratory mouse, C57BL/6, and gradually began to form standard conditions for vivariums (note: a vivarium is a room that is intended for keeping laboratory animals). We already know more or less everything about the laboratory mouse and it can be considered as an object of comparison for a naked digger. A naked digger is also a rodent. Of course, they and the mouse are evolutionarily far from each other, but we can still make some comparisons. So we can figure out how to keep a naked digger. Yes, of course, these are not standard cages, these are mazes, but, nevertheless, this is a room, this is a table and some kind of maze, these are still more standard conditions of detention. For the maintenance of other animal species that are also interesting for the study of aging processes, there must be special conditions of detention, it is not always possible to afford it, but it is very interesting and they are being studied. But here, too, the question arises: with what to compare? We can say that a mouse lives so long, and what are its physiological characteristics, what is its lung structure, the structure of intracellular organelles, and so on. When we study the naked digger, since he is a relatively close relative of them, also a rodent, we see that his development is already on a different path, or rather, it goes the way a mouse does in embryonic development and in the early postnatal period.
Could you share your plans for new research?
Of course, the research of naked diggers continues. We are also studying their behavior, large projects are underway to study the characteristics of their immune system, and cell physiology studies are also continuing, which can explain to us what allows a naked digger to prolong his youth, not age, while regenerating damage, because the most important questions we want to get answers to are how he is at a fairly mature age, has remained active for more than thirty years. And the main question is how we can continue an active and happy life in our old age, because, for example, in a naked digger, even the queen does not lose fertility with age and can actively reproduce. They do not suffer from senile diseases, which is also an important aspect, because we see how the mouse ages with age, as, in principle, many other organisms do. We see how she turns gray, benign or malignant tumors form, vision problems occur, that is, absolutely all senile human diseases manifest themselves in mice, and we see how the mouse ages. Regarding the naked digger, I can show both a 13-year-old and a naked digger born last year, visually they do not differ in any way: neither in size, nor in the number of wrinkles, nor in the activity of movement.
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