Author: Jeremy Borniger

That Homeostat’s Got Rhythm!

Biological stability, or ‘homeostasis’, where an organism works to maintain an internal ‘steady state’ in response to the environment, is a concept familiar to all modern biologists. At all levels of organization, from cells to entire organisms, negative and positive forces act in a yin and yang fashion to dynamically respond to the environment and re-establish balance. In humans, for instance, our temperature ‘set point’ is ~98 °F. In response to an infection, our systems respond by raising the ‘set point’ via changes in neuronal activity in the hypothalamus (a key brain region in the regulation of temperature). This produces a fever, which facilitates immune system function and stifles the growth of the invading pathogen. When allowed to run rampant, however, fever can be detrimental to the health of the organism and eventually lead to death. This highlights the importance of precisely regulated homeostatic mechanisms in maintaining health and preventing disease.

If your education in the life sciences was similar to mine, a lot of emphasis was placed on homeostasis, with little if any placed on an equally important concept: biological rhythms. For a long time, researchers disregarded unexplained daily variations in what they were studying (like temperature, blood pressure, growth hormone levels…) as ‘noise’ rather than true biological phenomena.  Indeed, until the latter half of the 20th century, research in ‘biological rhythms’ was lumped into an unfashionable category along with fringe subjects, including astrology and ‘mood rings’.  I wrote this post aiming to address misunderstandings in the relationship between homeostasis and biological rhythms, and share some cool and interesting real world examples that highlight this relationship and the value of biological rhythms.

Temperature regulation shows how the set point (or “homeostat”) can adapt in response to challenges from the environment to aid in survival (a process called allostasis). To add another layer to this, wouldn’t it be even more advantageous for an organism to pre-emptively change its set point to coincide with predictable environmental challenges (i.e., those that occur with some predictable frequency)?  In humans, for instance, body temperature and cortisol rise during the day to promote alertness, while growth hormone and melatonin secretion peak at night to aid in rest and recovery. At first glance, these variations seem to fly in the face of homeostasis, which dictates that each of these factors should remain at a fixed point to ensure optimum function. The reality is that this point must move up and down over time because the obstacles an organism must face change throughout the day and the year. Biological rhythms govern these changes and help explain why they occur.

Jürgen Aschoff, a fundamental figure in biological rhythm research, described the link between homeostasis and daily rhythms in the mid-1960s:

Homeostasis is a shielding against the environment, one might say, a turning away from it. For a long time, this phenomenon has been taken as the prime objective for an overall organization in physiology; and it evidently has great survival value. But there is another general possibility in coping with the varying situations in the environment; it is, instead of shielding, ‘to turn toward it’; instead of keeping the ‘milieu interne’ stable, to establish a mirror of the changing outside world in the internal organization. This has one clear prerequisite; the events in the environment must be predictable, which of course is the case when they change periodically.’

Nicholas Mrosovsky provides the example of temperature regulation in the camel to provide a real life example of Aschoff’s point. A camel faces a major problem every day of its life: how to keep cool. It is too big to bury into the sand, there is hardly any shade, and it would quickly die of dehydration if it were to utilize evaporative cooling to dissipate heat through sweating. There is a fundamental opposition between water balance and temperature regulation. Evolution has given the camel the necessary tools to deal with this situation.

The camel offers a prime example of homeostatic ‘set point’ regulation over time (Credit: Wikipedia)

During the day, the camel’s body temperature can rise as high as ~106°F – a wicked and almost certainly lethal fever if found in humans. At night, however, when water is scarce, the camel drops its temperature down dramatically to ~93°F, which would classify as dangerous hypothermia in people. The camel drastically reduces its temperature to protect itself from the next day’s heat. Because it drops it temperature so low at night, it now takes longer to heat up following day. In other words, the camels’ ‘set point’ is not fixed; it varies in response to predictable environmental challenges.

An organism’s physiology isn’t the only thing that needs precise timing; its behavior is set to a rhythm as well. Animals must not only adapt to a spatial niche (e.g., canopy, tide pools) but to a temporal niche (e.g., nocturnal, diurnal). It’s not only what an animal does that’s important, but when it does it. The ability to predict future events (either consciously, or in the case of biological rhythms, unconsciously) is of paramount importance in passing on your genetic information to future generations. One dramatic example of precise timing is the 17-year cicada, which emerges in a predictable fashion after lying dormant for nearly two decades. Another is the short-tailed shearwater, a bird that arrives at its breeding site in mid-autumn on small islands north of Tasmania. All the individuals in the population lay their eggs between November 24th and 27th each year, and they hatch at the same time. The cicada and shearwater make use of their exquisite timekeeping machinery to overwhelm potential predators with their progeny, allowing more newborns to survive than would if offspring emerged over a longer period.

Predator avoidance most certainly played a role in shaping the evolution of biological clocks. About 20 years ago, Pat DeCoursey and colleagues at the University of South Carolina conducted a study to investigate the adaptive function of rhythms in behavior. They lesioned the suprachiasmatic nuclei (SCN; a brain structure that acts as the primary ‘time keeper’ in vertebrates) of wild eastern chipmunks and then released them back into the wild and followed their survival for the next two years. To control for the effects of the surgery itself, they also “sham” lesioned several chipmunks, and left their SCN intact. After just 3 months, only a single intact chipmunk had become the target of predators, while 40% of the SCN lesioned animals became lunch. These deaths were attributed to the animals being active when they were not biologically inclined to be (i.e., their ‘clock’ was broken), making them easy prey.

A short day (left) and long day (right) adapted Siberian hamster (Credit: Gregory Demas, Indiana University)

In many rodents that live at non-tropical latitudes, the shortening amount of light each day signals the approach of winter months before the really cold weather hits. Siberian hamsters, for instance, have evolved to tell the time of year by measuring day length (photoperiod). With just two bits of information: (1) day length, and (2) whether days are getting longer or shorter; the hamster can tell what time of year it is, and if winter is coming or going. When days get shorter, males rapidly reduce their body size by ~20-30%, put on an extra layer of newly white fur, and all but eliminate their reproductive organs….they won’t be doing any mating when the weather hits -50°C. In response to short days, white-footed mice (commonly found in Ohio), actually reduce the size of their brain to putatively aid in saving energy. Every year, species like these need to radically reorganize their bodies to adapt to their changing environments, or die. This involves changing that ever stable ‘set point’ drastically throughout the year.

I hope some of the examples I’ve described above help provide context for thinking about biological rhythms. I also hope that a discussion of these rhythms in addition to homeostasis will facilitate the implementation of them into early lessons on the natural world. With the increased use of artificial lighting, shift work, and trans-meridian travel, our biological rhythms are being tested in contexts in which we have not evolved. Disruption of these rhythms is only now being appreciated as a contributing factor to many diseases including metabolic syndrome, depression, and cancer.

Nothing is more interesting than discovering the remarkable strategies animals have evolved to survive in their (sometimes) extreme environments. By adding the additional ‘wrinkle’ of rhythmicity in physiology and behavior, animals can exploit environments at one time of day or year that would be dangerous or even lethal at other times! I am excited for the future of the still new field of ‘chronobiology’ (aka the study of biological timekeeping), and can’t wait to see what nature has in store for us next!

Many of the examples I describe above are discussed in more detail in the excellent “Rhythms of Life: The Biological Clocks that Control the Daily Lives of Every Living Thing” by Russell G. Foster and Leon Kreitzman.

Jeremy Borniger is currently a doctoral student in the Neuroscience Graduate Studies Program at The Ohio State University. He received his BA in anthropology with a minor in medical science from Indiana University and has worked with chimpanzeesorangutans and gorillas. In his spare time, Jeremy enjoys playing the piano, scuba diving, cooking, and writing and reading as much about science as he can. You can follow Jeremy on Twitter: @JBorniger

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Tumbling Through the Void: Navigating the Grad School Gap Year

It’s 2:30 AM. I lay awake drenched in sweat, stress and uncertainty. Thoughts like “what am I doing with my life?” or “is everything I’ve done just a big waste of time?” ferment and fester in my mind. Time is running out.  After this year I will be thrust from the warm embrace of undergraduate life into the unforgiving cauldron of the outside world.  I am not ready!

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Late during my senior year at Indiana University, I realized that I enjoyed academia, and didn’t want to join what is classically referred to as ‘the workforce’. I was part of a strange sect of people who relished in knowledge for knowledge’s sake, and would voluntarily devote untold hours in pursuit of it for little compensation. I was prime grad school material.

My problem was that I did not come to this realization until after grad school application season ended, which meant I was doomed to a ‘gap year’ between graduating and the next application cycle. I was scared that once I fell out of the academic ‘tree of knowledge’, I would never be able to climb back in. I immediately postponed my graduation to August 2011, and spent the entire summer completing my honors thesis, which was ultimately published in PLOS ONE.

Before I could waste any more time, I contacted a professor whom I had cultivated a good relationship with about working for him during my upcoming hiatus from academia. I secured a job as an assistant project director (APD) for The Semliki Chimpanzee Project in western Uganda. After majoring in biological anthropology, I was anxious to finally get into the field and get up close and personal with some of our closest relatives. This exciting assignment, however, would not start for another few months.  I therefore needed to find other ways to take advantage of ‘open time’.

I took this rare opportunity to return home and become one of the thousands of ‘twenty-somethings’ that live with their parents and sleep until well past noon every day. I was not simply taking advantage of free lodging and food…or at least that is what I told myself. Awaking in the wee hours of the mid-afternoon, I parked myself in front of stacks of grad school applications, GRE study guides and work books. I read as much as I could and went out on the weekends. Life was good. Devoting my time to making my applications the best they could be paid off, and I secured a spot in my top choice program. When I traveled to Uganda a few months later, I was extremely excited to explore a new part of the world without having to worry about my future when I returned.

When I joined the research project, the previous APD had more or less sabotaged the entire study site. He had been stealing funds and was illegally trapping animals and setting fires for unknown reasons. The car employees had used to transport food and supplies from the nearby small village of Karagutu (~30 km) to the study site had been totaled earlier that year. We were in dire straits. My job was to get myself to the study site, and rectify these problems while managing 4 Ugandan employees with a tentative grasp on English. I was also to collaborate with local authorities to combat poaching activities in the area, which had skyrocketed recently. Furthermore, I was to relocate the chimpanzees and try to complete a milestone in habituation efforts, the nest-to-nest follow.  I had no idea what I was doing, and….it was incredible. Being thrust into a completely new and unpredictable environment prepared me for graduate school like nothing else could.

Image Credit: Jeremy Borniger

I quickly became used to waking up at 5:30 AM and tracking chimpanzees through escarpments along the Ruwenzori Mountains until dusk both on and off our 50 km2 trail system. Breakfast consisted of tea and a chapati (flatbread) with hard-boiled egg. Lunch on the trail was another chapati and egg. Dinner was frequently millet bread with goat stew and matoke. I learned skills I never thought I’d have in my repertoire, like animal tracking, dung analysis, exotic plant and snake taxonomy, and snare/trap disarmament. By completely changing how I lived my life, the food I ate, and what my daily priorities were, I was unconsciously preparing myself for graduate school. After returning from Uganda, moving to central Ohio was a cakewalk.

I learned that there is no ‘wrong way’ to spend a gap year, as long as you are experiencing new things, and getting out of your comfort zone. Take some time and do something completely different. After spending some much needed time getting rejuvenated after college, throw yourself into something you would usually never think twice about. You’ll thank yourself later…I know I did!

photo_BornigerJeremy Borniger is currently a doctoral student in the Neuroscience Graduate Studies Program at The Ohio State University. He received his BA in anthropology with a minor in medical science from Indiana University and has worked with chimpanzees, orangutans and gorillas. In his spare time, Jeremy enjoys playing the piano, scuba diving, cooking, and writing and reading as much about science as he can! 

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