Five long-lived animals

Why do whales, bats and naked diggers live so long

Until recently, it seemed that most animals age in the same way as humans. But in recent years, researchers have found out [1] that even among mammals there are animals that are not subject to age-related changes in the form we are familiar with. Today, scientists suspect that at least fifteen species of animals do not age at all. Biophysicist Peter Fedichev told Post-science about several centenarians from the world of wildlife.

Naked Digger

Naked diggers / Smithsonian's National Zoo on flickr

The fact that some primitive animals, such as hydra and some worms, do not age, has been known to science for a long time. The life expectancy of different species varies many times, and therefore comparative studies of longevity often do not make direct sense. 

At the same time, there is a correlation in nature between mass and life expectancy: all large animals live longer [2]. Therefore, as soon as a small long—lived animal appears for its size, it immediately begins to be of great interest to researchers. The fact is that if he lives several times longer than he "should", based on his size, this indicates some new physical or biological mechanisms that his body managed to use.

The most studied representative of long-lived mammals to date is the naked digger: this rodent in captivity is able to live for about 40 years. For comparison: moles — animals of comparable size — on average live about 4-5 years. 

The first study of a naked digger was published in 2005 [3]. American biogerontologists have found out that he does not age at all like a person. If mortality begins to increase in people after 10 years of life, that is, the rate of dying, then in this rodent, on the contrary, with the achievement of a certain age, mortality stabilizes.

However, usually not all naked diggers become centenarians, but only females who surround themselves with males bringing food to their burrow. This way they are protected from environmental factors and danger from predators. The longer females live, the more they leave offspring and, accordingly, the better genetic selection works in favor of increasing life expectancy.

By the way, naked diggers do not just not age — they also do not change externally. A person can clearly see how old he is, but looking at a naked digger, it is difficult to determine how long he has already lived. This type of aging in science is called negligible. Studies show that not only the appearance of the naked digger does not change with age, but also molecular signs, such as the expression of various genes. Advances in comparative genomics even make it possible to transfer the genetic characteristics of this rodent to ordinary mice and thus obtain new centenarians.

Bat

Brandt's nightgown in the researcher's hand // photo made by Herman Lankreijer

Determining the age of bats as a result of an external examination is also not an easy task. In the first ten days of life, they have webs between their paws, which then disappear. After that, not a single sign indicates how old this animal is. Therefore, scientists study the genome of bats and mark them, that is, put rings with individual numbers on their paws.

In 2003, this helped scientists determine the age of the captured male Brandt's moth [4]. It was marked back in 1962, which means that this bat was already 41 years old at the time of its capture. This is 10 times longer than the usual life span of animals of such a small size (the weight of Brandt's moth is from 5.5 to 10 grams). Moreover, other species of bats also live long enough: an ordinary vampire is about 19 years old, a brown ushan and a small brown moth are about 30 [5].

There are several reasons for such longevity: bats are almost inaccessible to predators, multiply slowly and fall into hibernation (hibernation). Brandt's Siberian moths are in hibernation from September to mid-July. During this period, their body temperature decreases, all processes slow down. But this may not be the only reason for longevity: hibernating bats do live on average six years longer, but not all bats practice hibernation.

But studying their genes can give more precise explanations. The authors of one paper claim [6] that Brandt's moth and some other long-lived mice have a unique genetic mechanism, which is probably the reason for their longevity. These animals also use an unusual way of maintaining telomere length and retain high expression of DNA repair genes throughout their lives [7]. It resembles a genetic mechanism involved by a naked digger.

Bowhead Whale

Bowhead whale off the coast of Alaska // Bering Land Bridge National Preserve

In nature, life expectancy, as a rule, begins to grow only in animals at the top of the food chain. For example, if nothing happened to a bowhead whale in childhood, if no one ate it and it managed to grow up, then now the length of its life will depend on how many offspring it will leave. The longer the whale lives, the more of its own kind it will reproduce. So the genes of longevity will be fixed in his offspring.

Unlike other whales that swim into polar waters only in search of food, the bowhead whale constantly lives in the cold seas and oceans of the Northern Hemisphere. But, despite the harsh living conditions, scientists managed to study it well. The average life span of a bowhead whale is about 40 years, but individuals can live for more than 200 years [8]. It claims to be the longest-lived mammal and until recently held the first place in life expectancy among vertebrates.

Shark

Greenland shark in Admiralty Bay // Bering Land Bridge National Preserve

From this pedestal, the Greenland whale was displaced only by the Greenland polar shark, which lives in the northern part of the Atlantic Ocean. In 2016, an international team of scientists published an article that this species of shark can live at least 272 years, and the largest representatives live up to 512 years [9]. The researchers came to these conclusions after conducting a radiocarbon analysis of the lens of the eye of several polar sharks. There are no exact explanations for such a life expectancy yet, but there is a version that their longevity may be affected by metabolism slowed down due to low water temperature.

The white shark also lives to old age. It lives in all terrestrial oceans except the Arctic, is one of the largest predatory fish and is considered the most dangerous for humans among sharks [10]. Previously, researchers believed that its life span was about 20 years, but not so long ago they came to the conclusion that individual representatives of the white shark can live up to 73 years [11].

Albatross

Albatross Wisdom // John Klavitter, U.S. Fish and Wildlife Service

The longest-lived bird in the wild is a female dark-backed albatross named Wisdom. In 1956, she was first caught, her age was determined (she was about 5 years old) and ringed, that is, they put a ring with a unique number on her paw. 46 years later, in 2002, scientists again caught Wisdom and began to observe her.

In the wild, dark-backed albatrosses lay one egg once a year. Since 2006, Wisdom has been nesting and raising chicks annually. Her next cub hatched in March 2021 [12].

Externally, it is quite difficult to determine the age of an adult albatross. But if we take into account that, as a rule, these birds begin to breed at 7-9 years old, then in 2021 Wisdom should have been about 70 [13]. Many birds live for a long time, up to 30 (for example, a white stork, a blue gull) or even 40 years (a sandpiper is forty), and scientists have known about a fairly long life span of albatrosses for a long time [14]. And yet 70 years is really a unique age for a bird.

***

Every year, scientists discover new negligibly aging animals — those who live as long as possible and age without any special external signs. But even these centenarians are not immortal. Like humans, they age and die over time. It's just that their mortality does not increase with age. It is assumed that negligible aging may be associated with extreme living conditions and stress resistance.

Literature

• List of negligibly aging animalsAnAge Vertebrate Life Expectancy Database
• West G., 2017, Scale. The universal laws of growth, innovation, sustainability, and the pace of life in organisms, cities, economies, and companies, New York, Penguin Press.
• J. P. De Magalhanes, J. Costa. A database of vertical longevity records and their relation to other life-history traits // Journal of Evolutionary Biology. Advance online publication 10 June 2009.
• J. P. de Magalhaes, J. Costa, G. M. Church. An Analysis of the Relationship Between Metabolism, Developmental Schedules, and Longevity Using Phylogenetic Independent Contrasts // Journal of Gerontology. 2007.

Portal "Eternal youth" http://vechnayamolodost.ru