600 Million Years of Jet Lag

Research Blogging / by Dave Munger /

Although the common ancestor of sea anemones and humans would look nothing like us, it still shares one of our basic traits: the capacity to experience jet lag.

Credit: Flickr user poplinre

At first glance, a sea anemone doesn’t seem much like a human. It’s a creature from the tidal zone, affixed to the rock or coral below, and without most of the anatomical features associated with humankind: It has no arms, legs, ears, eyes, or nose. It almost seems more like a plant than an animal. Anemones don’t even have a brain; instead their nerves form a network distributed throughout the body; each nerve cell can communicate with its neighbors, but no central structure controls the entire organism.

But a study published last month shows that anemones share one trait with humans: They, like us, are susceptible to jet lag. Like humans, anemones have a strong circadian rhythm, an activity cycle kept on a roughly 24-hour period by built-in biological clocks. It’s your circadian rhythm that contributes to feeling groggy at night and alert during the day. The study, led by Adam Reitzel, was discussed both on It Takes 30, the blog of the Harvard Systems Biology Department, and Dormiviglia, by Allison Brager, a physiology graduate student specializing in circadian rhythms.

Reitzel’s team wanted to understand the early evolution of circadian rhythms in animals, so they systematically studied how anemones respond to changes in the day-night cycle. Evidence from paleontology and genetics suggests that the common ancestor shared by animals with bilateral symmetry (like humans and insects), and those with radial symmetry (like anemones and jellyfish), lived over 600 million years ago. But even then, the Earth had days and nights like it does today, so it’s likely that the ancestors of both humans and anemones had some form of circadian rhythm. Humans rely on eyesight to hunt and gather food, so it makes sense for us to rest at night when those activities are more difficult. Our internal clock reminds us to get up in the morning even on dark, cloudy days, or when we are sleeping in dark shelters. Anemones might have similar time-driven needs, and so having an internal clock like humans would also make sense.

Biologists know that several genes in humans are responsible for our circadian rhythms. Anemones, it turns out, have comparable genes, and Reitzel and his colleagues devised tests to see if they functioned in comparable ways as well. The researchers placed anemones collected from the wild in tanks, and then varied the lighting in day-night cycles. Similar to how a circadian gene in humans responds to daylight, the anemone version of that gene responded to blue light, suggesting that the animals might be particularly attuned to moonlight. Not all of the anemone circadian genes behaved like their human analogs, which was no surprise: Human circadian genes also differ from those of other animals in similar ways. But, just like humans, the anemones seemed to suffer from “jet lag,” which is simply a delay adapting their rhythms when the day/night cycle is changed (not known is whether jet-lagged anemones experience cravings for ham and cheese omelets at 11 p.m.!).

This suggests that some aspects of circadian rhythms are shared by all animals, and may have been present over 600 million years ago in the common ancestor of anemones and humans. The research was published in PLoS ONE last month.

But not all animals share the same sorts of circadian cycles. Last April, chronobiologist and organizer of the annual ScienceOnline conference Bora Zivkovic explained the results of a study published in the March 2010 Current Biology. While mouse cells kept in culture show regular circadian cycles for days, the cycles in the same cells from reindeer decay much faster. This just might mean that a reindeer would be immune to jet lag because its circadian cycles are remarkably adaptable. In fact, they are almost completely absent for much of the year, when the polar animals live in 24-hour daylight (or darkness, in the winter) — since there’s no difference between day and night, a daily clock is not necessary. During the constant daylight of summer, reindeer are equally able to forage for food and equally susceptible to predators, day or night. So they should use other indicators (like availability of food or shelter) to decide whether to be active or rest. But Zivkovic points out that reindeer do have some response to the 24-hour day/night cycle. In spring and fall, when even their far northern habitat experiences both daylight and darkness, reindeer use that seasonal pattern to set their annual internal clock, enabling them to breed and migrate at the right time of the year.

Whether we’re adapting to jet lag or working the night shift, many humans might feel that circadian rhythms are more of a bother than they are worth. But think of it this way: If humans all slept and woke at random times, then it might be even more difficult for us all to get along. Without the dominant day-night cycle guiding our daily lives, how would we ever agree on times for meetings, meals, and other social activities? On the other hand, maybe that would be preferable to that annual ritual most of us share: The struggle of adapting to Daylight Saving Time.

Dave Munger is editor of ResearchBlogging.org, where you can find thousands of blog posts on this and myriad other topics. Each week, he writes about recent posts on peer-reviewed research from across the blogosphere. See previous Research Blogging columns »


Originally published October 13, 2010

Tags biology evolution

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