African elephants were the “melepasmu” mammals

African elephants were the “melepasmu” mammals

South African and American scientists have discovered that adult African elephants (Loxodonta africana) very little sleep.

Two wild female elephants observed by the researchers, on average, slept about two hours a day. This is a very short time of sleep among mammals recorded so far. The study is published in PLoS ONE.

Scientists have long been interested in how the flow of physiological processes, including sleep, in the largest living organisms. Elephants are the largest land mammals, therefore, to study their physiology began a long time ago: the first study that examines the dream, the elephants, appeared in 1938. Earlier zoologists have found that elephants sleep mainly at night, for 3-7 hours per day. However, the vast majority of studies were conducted with the participation of elephants living in captivity in circuses and zoos. It is known that animals in captivity, in the absence of predators and with an abundance of food and water, sleep is much more than in the wild.

The authors of the new research studied two adult wild elephants that live in the Chobe National Park in Botswana. Animals wearing collars with GPS sensors and gyroscopes, and to the trunks attached actigraphy device with a built-in accelerometer that registers the number of movements per unit time. They are used to monitor characteristics of sleep. To study the sleep of elephants, tracing their brain activity, it was impossible. Elephants have a very thick skull, so to implant the electrodes that register brain activity, would need surgical intervention, for ethical and technical reasons, it was unacceptable.

As was shown in experiments with elephants in captivity, the movement of the trunk reliably determine that the animal is asleep or awake. The authors believed that the cows are sleeping, if actigraph did not record movements of the trunk for five minutes or longer. Observation of animals was performed continuously for 35 days in April-may 2014.

The researchers found that on average, elephants sleep for about two hours a day, during the night. The day the animals were awake

However, their dream was multiphase, that is, they sleep and Wake up 4-5 times a night and slept on average 20 to 65 minutes per session. According to the testimony of actigraphs, during the experiment both cows were awake several times within 45-48 hours. During this time the animals were more than 30 kilometers, maybe, escaping from poachers or predators. Interestingly, in the following days the elephant had slept no more than usual.

Using the gyroscope built into the collar, scientists have determined the position in which slept an elephant, standing or lying down. It turned out that lying animals slept in only 10 days from 35 during which we conducted observations. This may indicate that they spent very little time in REM sleep, which may be necessary for memory consolidation (transfer of information from short into long term memory) and the learning process. The study showed sleep, the elephants, the signs of REM sleep (rapid eye movement, decreased muscle tone) were observed only in animals sleeping lying down. On the other hand, according to lead author of the study, Gender of Manzher (Paul Manger) from the University of the Witwatersrand in Johannesburg, perhaps the elephants do not need REM sleep, like whales or dolphins. Or do they remain in this phase for 5-10 seconds when sleep standing up.

Zoologist John Line (John Lesku) from La Trobe University in Melbourne, Australia, who was not involved in the study, believes that it is important to understand how changing the pose and motion of the trunk of elephants during wakefulness and different sleep stages. “For example, ruminant animals during sleep can stand with half-closed eyes and even chewing gum. So perhaps the elephants actually sleep longer than expected,” he says.

The duration of sleep, the elephants were the lowest among all the so far studied mammals

Other large animals sleep much longer: gray whale — at least nine hours a day, and the other large African mammal is the giraffe more than 4.5 hours. The next “short-lived” the elephants were domestic horses, on average sleeping for 2.5 hours per day.

Ekaterina Rusakova

Comments

comments