Science: Strange Nature: Elephant seals drift off to sleep while diving far below the ocean surface

[They are mammals so they need to breathe, yet they still manage to get a bit of sleep. Jan]

A new analysis of elephant seal brainwave patterns has revealed that these mammals take short naps while holding their breath on deep dives, averaging just 2 hours of sleep per day during their long trips at sea. The findings have been published today in the journal Science.

For many years, researchers have been mystified about how the northern elephant seal, (Mirounga angustirostris), one of the world’s elite divers, gets enough sleep when it forages at sea. During these trips, which can last up to 8 months, the seals are constantly diving, both to avoid predators such as killer whales and because their colossal energy needs compel them to keep searching for food. But unlike cetaceans and ‘eared’ seal species (such as sea lions), elephant seals cannot perform unihemispheric sleep, where one half of the brain rests and the other half remains alert.

This left an intriguing, unanswered question – when and how do elephant seals sleep?

The answer has now been revealed by a new study where, for the first time, scientists recorded the brain activity of a free-ranging, wild marine mammal. The results show that elephant seals take short naps while diving deep below the ocean’s surface. Furthermore, wild seals average just 2 hours of sleep per day when at sea – rivalling the record for the least sleep among all mammals, currently held by African elephants.

The research team, led by Dr Jessica Kendall-Bar (UC San Diego’s Scripps Institution of Oceanography) as part of her dissertation at UC Santa Cruz with Drs Terrie Williams and Daniel Costa, developed a bespoke tool to record brain activity (electroencephalogram, EEG) data in wild elephant seals during their normal diving behaviour at sea. The EEG sensors were secured to the seals using a neoprene headcap, which the researchers recovered when the animals returned to the beach. The seals carried a small data logger to store the EEG data alongside time-depth records and motion sensing data that allowed the researchers to track the seals’ movements along with the corresponding brain activity.

Ritika Mukherji, a Masters student and Rhodes Scholar in the University of Oxford’s Department of Neuroscience, contributed to the data analysis in the study. ‘It is an incredible achievement to have recorded such high-quality data in a wild mammal freely moving in such an extreme environment. Not only were we able to identify periods when the seals were asleep, but we could also distinguish the main different phases of sleep, that is slow-wave sleep (SWS) and rapid-eye-movement (REM) sleep.’

The system collected data from 13 juvenile female seals diving in Monterey Bay, California. Using this data, the researchers then developed a high-accuracy sleep identification algorithm that could detect periods of inactivity from recorded diving data. This enabled them to estimate sleep quotas for 334 adult seals using dive data recorded over several months during their foraging trips.

The results are remarkable for documenting the first known case of REM sleep in a wild, unrestrained marine mammal. Unlike other marine mammals that perform unihemispheric sleep and maintain some motor control, elephant seals really seem to “let themselves go” completely during these dives.

Ritika Mukherji, Department of Neuroscience, University of Oxford

The results showed that the seals sleep for about 10 minutes at a time during deep, 30-minute dives. During SWS, the first deep sleep stage, the seals still had postural control and maintained a controlled glide downwards. After a few minutes, they transitioned to REM sleep and entered sleep paralysis, which caused them to turn upside down and drift down in a “sleep spiral.” In shallower waters over the continental shelf, elephant seals sometimes slept motionless while resting on the seafloor.

The study also revealed that elephant seals apparently repay their massive sleep debts by switching to a different regime once they return to dry land. Once they were out of the water and safe from predators, their daily sleep time was over 5 times higher than when at sea and over 10 hours per day. Certain migratory birds are known to similarly fluctuate between extreme variations in daily sleep duration, but this is the first time such behaviour has been recorded in mammals.

Remarkably, Ritika’s involvement in the study was due to serendipitous chance, when she came across Jessica Kendall-Bar’s website whilst she was an undergraduate studying Zoology at Miranda House, University of Delhi in India. ‘I sent Jessica a message to say how interested I was in her work and she responded two minutes later to ask if I would like to help her with a new study. I ended up working on the study for one and a half years, which ultimately shaped my ambition to study neuroscience as a postgraduate.’

Ritika first led a comprehensive review of all previous studies to assess sleep in wild and laboratory animals, then used this to help establish criteria to determine when an animal is asleep or not. She then helped to analyse the electrophysiological datasets recorded from the seals, scoring different brain wave patterns as indicating awake periods, SWS, or REM sleep.
‘It has been a dream come true to work on this study, even though the work was challenging at times, particularly because most sleep studies have focused on humans with few looking at animals. But it has really influenced my current long-term career ambition, which is to become a researcher in veterinary science, helping to develop new non-invasive methods to study wild animals. Jessica has been the best mentor I could ask for.’

Dr Jessica Kendall-Bar said: ‘Ritika led an extensive and rigorous review of the literature on the methods employed across laboratory and wild sleep studies to help establish that our study was novel in that it is the first to record sleep in wild, free-ranging marine mammals. While reading over a hundred papers on sleep might deter some, Ritika has continued on to study sleep at Oxford with one of the top sleep research groups. It has been a pleasure to work with and learn from her as well as the other interns in my group.’

The study ‘Brain activity of diving seals reveals short sleep cycles at depth’ has been published in Science.


Science: IMPORTANT: Mars meteorite that crashed to Earth contains ‘huge diversity’ of organic compounds

A Martian meteorite that crashed to Earth 12 years ago contains a "huge diversity" of organic compounds, including one that has never been seen on Mars before, a new study has found. The findings could help scientists understand more about the Red Planet’s habitability and whether it potentially once harbored life, researchers said.

The Tissint meteorite broke apart in the sky above the city of Tissint in Morocco on July 18, 2011, showering fragments of the space rock across the surrounding desert. The meteorite, which formed on Mars hundreds of millions of years ago, was likely ejected from our cosmic next-door neighbor by a cataclysmic event before being caught in Earth’s gravitational field. It is one of only five Martian meteorites witnessed by people as it crashed into our planet.

In a new study, published Jan. 11 in the journal Science Advances, researchers analyzed fragments of the meteorite and found examples of at least five different types of organics compounds.

The new study represents "the most comprehensive catalog ever made of the diversity of organic compounds found in a Martian meteorite or in a sample collected and analyzed by a rover," researchers wrote in a statement.

Organic compounds are molecules that contain carbon atoms bonded to atoms from one or more other elements — usually hydrogen, oxygen, nitrogen and sulfur, as well as others. These compounds are highly abundant in all lifeforms on Earth, which means their presence in space rocks could potentially indicate the existence of life elsewhere in the solar system. However, some organic compounds can also be formed by non-biological processes, so scientists cannot know for certain whether such compounds are a sign of life on other planets.

The Tissint meteorite contained organic magnesium compounds, which are "extremely abundant" throughout the meteorite and have never been detected in Martian samples before, researchers wrote in the study. The team believes that these compounds were formed in the high-pressure and high-temperature conditions of Mars’ ancient mantle (the layer beneath Mars’ crust), meaning they are non-biological and could reveal clues about how the Red Planet’s deep interior was shaped.

The researchers also uncovered several other compounds within the meteorite, including aliphatic branched carboxylic acids — compounds that have similar structures to amino acids that make up proteins; aldehydes — compounds where a carbon is double bonded, or shares multiple electrons, with an oxygen atom; olefins, or hydrocarbons with one or more carbon atoms double bonded to each other; and polyaromatics — complex hydrocarbons that include multiple ring structures.

The new study of the Tissint organics is the most detailed analysis of any Martian sample to date.

The new study of the Tissint organics is the most detailed analysis of any Martian sample to date. (Image credit: Shutterstock)
This is not the first time organic compounds have been discovered within a Martian meteorite. The Allan Hills 84001 meteorite, or ALH 84001, which crash-landed in Antarctica in 1984, contained several organic compounds; their discovery sparked years of debate about whether these compounds could have been formed by ancient Martian life forms. But in July, 2022, researchers discovered that the compounds within ALH 84001 were likely created by basic geological reactions billions of years ago.

Although none of these organic compounds identified in the new study are obvious biomarkers for alien life, the researchers note that they can still help teach scientists new things about our cosmic neighbor, potentially including whether the ancient geological conditions on the planet may have favored life.

"Understanding the processes and sequence of events that shaped this rich organic bounty will reveal new details about Mars’ habitability and potentially about the reactions that could lead to the formation of life," study co-author Andrew Steele, an astrobiologist at the Carnegie Institution for Science in Washington D.C. and a mission scientist with NASA’s Perseverance and Curiosity rovers, said in the statement.

But future missions to Mars are needed to expand our understanding of the Red Planet before we can say more confidently whether or not life once flourished on Mars, the researchers said.

"The question of whether it [life] ever existed on Mars is a very hot research topic that requires deeper knowledge of our neighboring planet’s water, organic molecules and reactive surfaces," study lead author Philippe Schmitt-Kopplin, a biogeochemist at the Technical University of Munich in Germany, said in the statement.