Baby Dolphins Don't Sleep
July 14, 2005
by Emily Hager

In the search to understand why we need a certain amount of sleep, scientists have discovered that dolphins and killer whales survive on almost no sleep for the first months of life. This ScienCentral News video has more.

The Young and the Restless

Being a new mother is exhausting, but if you're a dolphin or a killer whale, you may not be getting any extra sleep-time to recover, in fact you may not be getting any sleep at all. Scientists in California and Russia have discovered that both dolphin and killer whale mothers and calves apparently go with no sleep for the first few months of the new baby's life.

"These marine [animals], who are mammals like us, thrive without any extended periods of sleep for over a month," says lead researcher and neuroscientist at UCLA's Sepulveda VA Ambulatory Care Center Jerome Siegel.

Siegel and his colleagues monitored two killer whale and calf pairs at SeaWorld San Diego, as well as four dolphin and calf pairs at the Gelendgick Dophinarium near Russia's Black Sea coast. They reported in the journal Nature that during the first postpartum month these animals were awake "24 hours a day," but gradually increased the amount of time they spent sleeping as the calf aged.

"We all feel like, they must be incredibly tired, but they don't seem to be," says SeaWorld's senior veterinarian Jim McBain, who witnessed much of Siegel's team's research on the killer whales.

Siegel says the sleep patterns he and his colleagues observed in the babies are "just the reverse" of all other mammals, which normally sleep the most after birth and gradually taper down to adult levels as they age. "This is a challenge for the idea that sleep is necessary for brain and body growth, because during this period of very rapid development in killer whales, and we've also seen it in dolphins," says Siegel, "There's actually the lowest level of sleep behavior of the animals' entire life."

The researchers do not know how the mothers and their babies can live on so little sleep, though they expect it's a behavior the babies evolved to keep moving and stay warm and safe in colder, wilder waters. For the mothers, it is most likely part of their protective nature and also to create what's called a "slipstream" beneath their bellies where their calves, who are not very strong swimmers, can coast through the water easily.

Minimalists

But dolphins and killer whales — members of what scientists call the larger marine mammal order "cetacea" — are known for their minimal sleep habits. In the wild, adult cetaceans sleep with one eye open. Research by Humboldt State University marine biologist Dawn Goley and Siegel's colleague Oleg Lyamin have shown that when cetaceans have their right eye closed, the left side of their brain is asleep, and vice versa. According to the research, this "uni-hemispheric" sleep is associated with slow, inactive brainwaves in the sleeping part of the brain.

Gregory Stone, Vice President for Global Marine Programs at the New England Aquarium, says it's similar to lazing in a hammock on a Sunday afternoon, "When you go half asleep and shut some of your circuits down."

Stone says, "We didn't see any eye closure during this early period after birth in either the mother or the new born, which is what convinced us that even by the standards of [cetacean] sleep, they're not having the brain activity pattern seen in sleep."

Cetaceans sleep this way because unlike humans, they have to make a conscious effort to breath. Keeping half of their brain awake, allows them to be alert enough to surface and breathe as well as being aware of potential dangers.

Though there are few dangers at places like SeaWorld, the researchers say the behavior they observed has nothing to do with the animals being in captivity, and that wild dolphins and killer whales probably behave similarly.

"The ocean is a very different kind of environment from land," says Siegel. "There's no safe place to sleep in the ocean, [and] there's no warm place to sleep in the ocean, so these two factors may account for the animals' behavior."

McBain says, "If an animal is going to have a chance to sleep more, it would be here at SeaWorld [rather] than it would be in the wild."

Stone also agrees that this is an evolutionary behavior that "transcends" the animals' environment. "I can't imagine why they would have a different sleep pattern in captivity than in the wild," says Stone.

Another Interpretation

But there's a different way to interpret these "compelling" findings says Dawn Goley. "Either they don't sleep or they sleep in shorter bouts of time," she says.

In order to better understand their sleep patterns, Goley says the researchers need to do a neurological, not just a behavioral analysis, of the animals. She says remotely monitoring the brainwaves of the animals would help further the understanding of their sleep behavior.

As their work progresses, the researchers plan to study killer whale and dolphin brains to see if there is a structural explanation for their sleep habits, as well as to determine if changes in brain chemistry might be limiting their sleep after birth. If they can unravel this mystery, they may ultimately have a better understanding of why we humans need sleep, what it takes to go without it, and how to treat sleeping disorders.

This research was published in the June 30, 2005 issue of Nature, and was funded by the National Institutes of Health, the National Science Foundation, Department of Veterans Affairs, Utrish Dolphinarium and DARPA.

Original source: http://www.sciencentral.com