Spiders have extremely short circadian rhythms

By ANNA CHEN | November 30, 2017

For many college students, the start of a new day is marked by the shrill ring of an alarm clock in the morning and the end is dictated by our brains becoming too exhausted to process the textbook we are reading at the end of the night. But, in the absence of alarm clocks or a study schedule, when would we wake up and go to sleep?

Our sleeping and waking patterns are determined by a biological clock, regulated by the increase and decrease of hormones. In past studies, researchers have found that in extended periods of total darkness, organisms rely on their biological clocks, or circadian rhythms, to determine when they are active and when they rest.

The circadian rhythm of humans runs, on average, about 10 minutes longer than Earth’s 24-hour day.

Circadian rhythms have been a popular area of study for many years; the genes responsible for regulating the biological clocks in humans were determined recently.

Even more recently, a team of researchers made a puzzling finding — a group of three spider species called trashline orb-weavers have shockingly short internal clocks of just 17 to 19 hours.

What is the significance? For the spiders to have such a short biological rhythm means that every time the sun rises on a new day, instead of having their clocks reset 10 minutes like ours are, the spiders’ clocks must be shifted the equivalent of five distinct time zones. Unlike us, these spiders can survive this drastic time shift effortlessly.

Darrell Moore, a neurobiologist at East Tennessee State University, discovered the short biological clock period of the orb-weaver spiders while studying how the spiders tend to switch behaviors throughout the day.

Trashline orb-weavers build a line of “trash” out of dead bugs, feces and leaf litter, through the center of their circular webs. They use this trashline to disguise themselves from predators as they hide amongst the debris. After nightfall they become very active. Their peak activity is about three to five hours before sunrise.

To monitor their curious behavior, scientists caught wild trashline orb-weavers and took them to the laboratory. These spiders’ activities were tracked using an infrared sensor, which would be triggered when spiders were active and moved around.

Then, several days later, the spiders were monitored during weeks of continuous and total darkness, and their cycles of activity and rest revealed their unusually short biological clock periods, especially compared to some spiders with very long internal periods, up to 29 hours.

Natalia Toporikova, a biology professor at Washington and Lee University, described trashline orb-weaver spiders as “spiders without jetlag” in an interview with The Washington Post.

Their flexibility and adaptability are so impressive that she has decided that these spiders, instead of cockroaches, will conquer the world in the case of a “nuclear holocaust.” At the very least, they will offer insight on circadian rhythms in different species and their effect on animal function.

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