On the left, shifting hormone levels over time. On the right, work (gray) and sleep (black) hours of NASA staff on Martian time gradually cycle around the clock.
Mars has an ever-so-slightly longer day than we do: 24 hours and 39 minutes, to be exact. To control solar-powered rovers like Phoenix and Curiosity, NASA teams must shift their sleeping cycles to match, and it’s a lot harder than it sounds: that fraction of an hour extra means that their sleep schedules creep every day, so while 1 pm might be the middle of the night one week, say, it will have become breakfast time by the next. Staying on Mars time is so grueling that staff for the Sojourner rover in 1997 bailed on the schedule a third of the way through the mission.
FA=high-fat, ab libitum (eat-at-will) diet, FT=high-fat, time-restricted diet, NA=normal ab libitum (eat-at-will) diet, NT=normal diet, time-restricted
Diets tell you what you eat, but a new study suggests when you eat matters too. Of two groups of mice who were fed the same high-fat diet, the mice who could eat around the clock were much heavier than those who had food restricted to eight hours per day, in a new study published in Cell Metabolism.
Researchers in the study gave the mice a special high-fat chow, 61% of whose calories come from fat (compared to just 13% in normal feed). The mice who chowed down all day and night became, unsurprisingly, obese, but the ones who ate the same amount of hi-fat food in only eight hours per day did not. Their body weight was comparable to mice fed an equivalent amount of calories on normal feed.
A fruit fly in its natural habitat
In circadian rhythm research, the single best-studied organism is probably the fruit fly. It was through grinding up the heads of countless flies that scientists discovered molecular clock genes, which were then found to play similar roles in humans. But when it come to how actual fly behavior changes in a 24-hour period, a recent study questions whether conventional lab wisdom is wrong. A new paper in Nature put those same lab-bred fruit flies in a natural habitat and observed bursts of activity at unexpected times.
Two set of experiments, one in Italy and another right in the backyard of the lead researcher in England, found that flies are diurnal. That means they’re most active during the day, specifically the afternoon with small upticks in activity during dawn and dusk. While this may not sound exciting by itself, it upends decades of lab research that said fruit flies take a “siesta” during the day and have dramatic bursts of morning and evening activity. This behavior is so well-accepted that there are neuron clusters of the fly brain called morning and evening oscillators whose activity corresponds to the bursts.
Outdoors, however, temperature fluctuations and the gradual rising or setting of the sun offer much richer information than a temperature-controlled incubator where lights flick on at ZT 0 and off at ZT 12. (ZT stands for Zeitgeber Time, which means “time giver” in German.) Since the morning burst of activity comes just before sunrise, scientists had thought it was governed by an internal molecular clock. Data from this new study suggest this morning activity is actually set by warming temperatures leading up to sunrise.
The problem: Scientists want to study our circadian rhythms, our bodies’ internal clocks, and they can do so on the genetic level by examining how gene expression changes throughout the day. But ordinarily that would require sampling a person’s blood or skin multiple times a day, an ordeal few of us would want to endure.
The solution: hair.
Makoto Akashi’s team reports today in the Proceedings of the National Academy of Sciences that hairs, be they from the beard or head, contain the telltale signature of RNA activity that shows when we humans are at our peak activity level for the day.
A new experiment has shed light on how the monarch butterfly executes its impressive 2,000-mile migration every fall, and all it took was a lick of paint.
Researchers already knew that the butterflies use the sun to guide them to the exact same wintering spot in central Mexico. But because the sun is a moving target, changing position throughout the day, biologists have long speculated that in addition to having a “sun compass” in their brains, butterflies must use some kind of 24-hour clock to guide their migration [Wired.com]. In a new study, published in Science, researchers determined that the butterflies have a second circadian clock in their antennae, which sense light.
The researchers conducted the test by holding the butterfly wings gently and dipping their antennas in enamel paint. The ones with black paint were unable to orient to the south, they found, while butterflies whose antennas were coated with clear paint had no trouble navigating [AP]. This proved that the antennae had to be able to sense light for the butterflies’ navigation system to operate, and also showed that the butterflies weren’t navigating by scent, as both kinds of paint interfered with the insects‘ sense of smell.
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DISCOVER: The Flight of the Butterfly
Image: Monarch Watch / Chip Taylor
Some lucky people don’t groan awake to the alarm clock when they’ve only gotten six hours of sleep–instead they pop out of bed, bright-eyed and invigorated and ready for a new day. Now, researchers investigating the phenomenon of people who don’t need as much sleep as the rest of us have found a rare genetic mutation that accounts for some cases of shortened sleep cycles.
The scientists were searching the samples for variations in several genes thought to be related to the sleep cycle. In what amounts to finding a needle in a haystack, they spotted two DNA samples with abnormal copies of a gene called DEC2, which is known to affect circadian rhythms [The New York Times]. When they looked up the volunteers who had given the two DNA samples, they found a mother and daughter who habitually get about six hours of sleep each night and report no ill effects.
Researchers have found fundamental differences between the brains of people who prefer to rise and greet the dawn each day, and those who don’t mind seeing a sunrise, but only if it’s at the end of a long night. A new study used brain scans and alertness tests to probe the brains of early birds and night owls, and found that people tend to favor mornings or nights based at least in part on how they react to a kind of competition in the brain [National Geographic News].
Two factors control our bedtime. The first is hardwired: A master clock in the brain regulates a so-called circadian rhythm, which synchronizes activity patterns to the 24-hour day. Some people’s clocks tell them to go to bed at 9 p.m., others’ at 3 a.m…. The second factor–called sleep pressure–depends not on time of day but simply on how long someone has been awake already [ScienceNOW Daily News]. Sleep pressure builds up as hours of wakefulness increase. The new study, published in Science, suggests that early birds are more susceptible to sleep pressure, giving night owls the advantage in stamina.