The Nature of Science

Showing posts with label circadian rhythm. Show all posts

When The Early Bird Is Also The Night Owl

Biology concepts – cathemerality, circadian rhythm, adaptation, predator/prey relations

One carnivorous and three vegetarian friends

stranded on a island – what could go wrong?

The 2005 movie ”Madagascar” had some animals that we recognize from zoos; a lion, a zebra, a hippopotamus, a giraffe. But who were the bad guys? They were called the “Foosa” but what kind of animal was the foosa? And who were those little primates they were trying to eat?

Being an island, Madagascar has developed ecosystems all its own. There are plants and animals that live there and nowhere else on Earth. This can lead to some interesting and exceptional behaviors and activities.

Tenrecs are a weird group. Different species can

be a few grams to over a kilogram, may have between

30 and 45 teeth, are related to elephants, and a have

a common anal and urogenital opening like birds. With

all that going on, being blue and yellow doesn’t seem

that weird.

Madagascar has its share of diurnal activity (daytime) and even more activity under the cover of dark (nocturnal). The streaked tenrec (Hemicentetes semispinosus, one of about 30 species) is crepuscular (active at dusk and dawn), so that activity pattern is covered as well. This black and yellow-striped cross between a hedgehog and a shrew (just by the looks of it, not by parentage) feeds on worms and other invertebrates. A study from early 2011 described a unique behavior from the tenrec, one that may cause us to include the cricket in the tenrec’s ancestry.

The quills on the tenrec come in two sizes, the long ones are for protection, but the shorter ones can be rubbed together to make high pitched (ultrasonic in many cases) sounds that can be used for communication or navigation. In the low light conditions of sunrise and sunset, scientists are considering the idea that tenrecs use stridulation (making sound by rubbing body parts against each other) to echolocate in their surroundings, similar to bats. They can also keep tabs on one another, communicating constantly with other tenrecs, even with a mouthful of worm.

The short spines on tenrecs are controlled by individual

muscles, so that one spine can be rubbed against another

to make noise.

Crickets, beetles, and some vipers stridulate, but the tenrec is a stridulating exception in two regards. One, it is the only mammal known to do so; and two, it is the only animal of any kind known to communicate both vocally and by stridulation. Madagascar would be a cool place to visit – weirdness like this is around every corner.

Even though the tenrec is a Madagascar native, I didn’t see him anywhere in the movie. Some animals are too weird even to be believable in a cartoon about talking animals.

The movie did feature a primate group from Madagascar, one that had a penchant for dance. Lemurs (from Roman mythology, lemurs = ghosts) are playful and energetic, and some are even said to dance, but I don’t think they crave house music like in the movie. The Sifaka verreauxi is called the dancing lemur, as it is the exception to four legged motility among the lemurs. S. verreauxi walks on two legs, but the outward turn of their hips make them sway back and forth, like they are dancing.

Lemurs of the genus Sifaka bounce around on two

legs to cover ground quickly. This looks like dancing, and

probably gave the movie makers the idea to turn the

lemurs into a group of party animals.

In the movie, I saw no less than seven different types of lemurs, but in truth there are about 100 lemur species and subspecies live on Madagascar and the nearby Comoro Islands (and nowhere else). Together, they are a microcosm of Madagascar activity patterns. Some lemurs species, like the large Sifaka verreauxi, are diurnal, while the smaller species, like the aye-aye, are generally nocturnal. Some are even crepuscular, active at both dusk and dawn (so they are not vespertinal or matutidnal). But the weirdest types of lemurs are those that don’t show any of these patterns; in fact, they show no pattern at all! If that isn’t an exception, I don’t know what is.

The lack of an activity pattern does have a name, cathemerality (from the Greek, cat = complete and hemera = day). Cathemeral animals are active for periods of the day and/or periods of the night. In some cases, the periods of activity are driven by competition, when competitors are resting or prey is active. In other cases, periods of activity might be influenced by the seasonal temperatures or even the phase of the moon.

Whatever the stimulus, cathemeral (sometimes called metaturnal) animals can sleep day or night and hunt day or night, with no period of adjustment needed. African lions are cathemeral, driven by hunger and the success rates of their hunts, or by a need to conserve water.

In Madagascar, the red-fronted lemur (Eulemur fulvus rufus) is cathemeral in activity, as is the blue-eyed black lemur (Eulemur macaco flavifrons). Among primates, only humans and this species of lemur have blue eyes. However, the males have black hair while the females are reddish, so there is no chance of little blonde-haired, blue-eyed lemurs.

It is called the blue-eyed black lemur, so why is it

reddish-brown? This species is sexual dichromatic;

picture above is of a female, only the males are black.

The blue-eyed black lemur sees in color and is generally adapted to diurnal living; this is witnessed by the increase of its nocturnal activity when there is a full moon and with the nocturnal light level in general. However, the blue-eyed lemur has at least some activity spread across the 24-hour day all year round. This is one of three cathemeral patterns of lemurs in Madagascar lemurs.

A second cathemeral pattern is seasonally driven. In summer, when the daylight hours are greatest, it is enough for some cathemeral animals to limit themselves to daylight activity, but expand their active hours a bit during winter, so they are active in both day and night. This is driven by a need to find sufficient food.

The third cathemeral pattern is one in which there is mostly diurnal activity in one season and mostly nocturnal activity in another season. This may be driven by changes in temperature or perhaps resource availability. In Madagascar, the tropical climate ensures that food is always available, and the lack of a winter means that the temperature ranges between 60˚F and 80˚F all year round.

Many scientists believe that cathemerality may be an transient evolutionary middle ground, that all the species that display cathemeral activity are merely moving from diurnal to nocturnal, or the opposite direction. This is also known as an evolutionary disequilibrium hypothesis, as opposed to the idea that cathemerality is a stable evolutionary strategy. A recent study using genetic markers across time (phylogenetics) indicate that there was a common ancestor lemur that was cathemeral as far back as 9-13 million years. This would indicate that cathemerality is VERY stable. These results therefore suggest that the three cathemeral patterns are related to stable patterns predation risk or food gathering.

However, the diets of the red-fronted lemurs and the blue-eyed black lemurs are very different considering that they are closely related species, called true lemurs (eulemurs, eu = true). Red-fronted lemurs eat only leaves, while blue-eyed black lemurs eat fruits. But they are both herbivores, and are both potential meals for a predator. This would be a good reason for being cathemeral; the lemurs can just choose to be active when the predator isn’t. Great idea, huh? Well, Madagascar’s biggest predator apparently read the lemurs’ playbook.

The fossa is not a cat, it is not a mongoose, it is not a monkey.

It is a predator and it is found only in Madagascar. It has

retractable claws, the same as all cats except the cheetah.

The fossa (pronounced foosa - get the connection to the movie?) is really Madagascar’s only big predator. It looks like a cat as it walks, and has retractable claws like most cat species, but its tail is as long as its body, like a monkey or a lemur. The fossa’s snout is more mongoose-like, as is the length of its body compared to the length of its legs. The film version of Madagascar didn’t do justice to the physical nature of the fossa; the bad guys pass for large cats.

The fossa spends much of its time up in the trees (it is arboreal) and chases the lemurs from tree to tree. Its long tail and sleek body design help it to move and maintain its balance as it moves through the branches. Most interesting, and an exception to mammal body design, the fossa’s outside digits on its rear paws are its biggest, this helps it to grasp the surfaces of the trees.

The long tail of the fossa helps it chase down

lemurs in the trees by improving its balance.

It also helps that the fossa hunts lemurs in

groups, using cooperative strategies.

Up in the trees we have the lemurs; some diurnal, some nocturnal, some crepuscular, and some cathemeral. What a buffet for the fossa! No matter what time he (or she) wishes to dine, there could be lemur on the menu, so the fossa has adopted cathemerality as well.

The movie was accurate in showing the fossas and lemurs active in both day and night now, but did the lemurs become cathemeral to get away from fossas? Maybe. The lemurs evolved before the fossa; were they cathemeral because they didn’t have to worry about predation, and a few species have stayed that way? Could be. Did the fossa become cathemeral to take advantage of the lemur smorgasbord? Nobody knows –yet. You can be sure that there are scientists who support each possibility.

Whichever way it happened, it points out a wrinkle that few people consider. Some animals can actually change their activity pattern. The shift is often in response to some ecological or physiologic pressure. Skunks are crepuscular - except for males in the mating season - they become diurnal.

Another example is the short-eared owl of the Galapagos Islands. The owls are crepuscular on islands that have a predatory buzzard species, but on islands without buzzards, the owls are diurnal. Finally, some anole species change their activity pattern from diurnal to nocturnal as the temperature rises. Even their color can change from green to brown as the temperature changes.

These shifts in activity patterns occur often enough that they can’t be called exceptions, but the majority of animals do hold a single pattern throughout the year. As such, nocturnal animals interact with other nocturnal animals and the same with diurnal animals. This isn’t a tough concept to grasp, even the movie got it right. Unfortunately, some folks in 1880’s Hawaii just didn’t seem to understand, and they are still dealing with the problems it caused.

Griffin, R., Matthews, L., & Nunn, C. (2012). Evolutionary disequilibrium and activity period in primates: A bayesian phylogenetic approach American Journal of Physical Anthropology, 147 (3), 409-416 DOI: 10.1002/ajpa.22008

For more information and classroom activities on cathemerality, lemurs, or fossa, see:

Cathemerality –

http://www.ips2004.unito.it/Sym_Curtis.html

http://www.ncbi.nlm.nih.gov/pubmed/16415576

http://www.hindawi.com/journals/ijz/2011/362976/

http://www.deepdyve.com/lp/taylor-francis/avoiding-commitment-cathemerality-among-primates-kyInyZRVTH

Lemurs –

http://www.ncbi.nlm.nih.gov/pubmed/16415576

http://www.nhbs.com/lemurs_of_madagascar_diurnal_and_cathemeral_lemurs_tefno_160645.html

http://www.lemurs.us/basics.html

http://nationalzoo.si.edu/Animals/Primates/Facts/FactSheets/Lemurs/default.cfm

http://www.globio.org/glossopedia/article.aspx?art_id=49

http://www.pbs.org/edens/madagascar/class1.htm

http://www.magpi.net/Community/Programs/Madagascar-Conserving-Biodiversity

http://www.lemurreserve.org/programs.html

http://www.animalcorner.co.uk/rainforests/lemur.html

http://www.actionbioscience.org/evolution/roberson.html

fossa –

http://animals.nationalgeographic.com/animals/mammals/fossa/

http://www.sandiegozoo.org/animalbytes/t-fossa.html

http://www.edgeofexistence.org/mammals/species_info.php?id=43

http://www.environmentalgraffiti.com/animals/news-one-weirdest-predators-earth-fossa

http://www.zooborns.com/zooborns/fossa/

http://www.pbs.org/wgbh/nova/madagascar/classroom/l2_intro.html

Form Follows Function - It’s About Time

Biology concepts – circadian rhythm, vision sense, adaptation, parasitism, form follows function

The sun and the moon are symbols of different

activity cycles. As with everything else, we have to give

them human characteristics (anthropomorphism).

Many animals are active in the day or the night, but not both. So what are humans, diurnal (active in the daytime), nocturnal (active in the nighttime), or something else?

Maybe humans are two species, because I know folks who can’t accomplish anything before noon, and do their best work after 11:00 pm, whereas I get up around 5:00 am and am pretty much useless after 8:00 pm.

Whether diurnal or nocturnal, organisms are physically and behaviorally adapted to their activity pattern. This includes the way they sense their environments. Diurnal animals are more likely to have color vision, while nocturnal animals may only see in black and white. The upside for nocturnal animals is greater visual sensitivity, so they can see better than diurnal animals in low light conditions.

The reasons for these different visual talents lies in the types of light receptors on the retina. Rods sense light, but only its presence or absence (white/black). Different receptors, called cones, detect various wavelengths of light (colors). Diurnal animals have about 5-10 times more cones than nocturnal animals (3 types, one for yellow, one for green to violet, and one for red to orange), but they only function in higher levels of light. Therefore, the greater number of rods in nocturnal animals allow for more sensitive night vision, a good thing to have if you are active after sundown.

Rods (yellowish) and cones (blue) are different light receptors located on the retina. Rods are more numerous and detect low levels of light. Cones are less numerous and sense colors of light, but require more light. As shown in the middle image, the tapetum is located beneath the retina in some animals, and can bounce light back to the retina. This bouncing around is responsible for animals glowing eyes at night.

Many nocturnal species have an additional adaptation to improve their night vision. Their retina has an iridescent layer called the tapetum lucidum that bounces the available light around so it may hit more rods. This improves sensitivity, but at a cost to acuity (the image gets a little fuzzier). When you shine a flashlight in the woods at night, the little pairs of reflections you see are the tapetum lucida of the animals looking back at you. The light bounces around inside the eye and some escapes back out through their pupils and that is what you see. Some look at your flashlight to see if you are a predator, others look to see if you are worth eating.

But not every animal with a tapetum lucidem is necessarily nocturnal. An interesting new study has looked at the visual system of the Peter’s elephant nose fish (Gnathonemus petersii). This weakly electric fish has a long nose-like appendage that was thought to mediate location and communication through electrical pulses. But scientists at the University of Cambridge have found that this fish has surprisingly good vision to go along with electrical impulse usage.

The elephant nose fish lives in the dark, murky waters of Central Africa. For this low light environment, it has evolved a unique retinal arrangement for its rods and cones. The cones are arranged in discrete packets, each housed in a cup lined with a tapetum lucidem. Behind these cones are the rods that work in lower level light. In this way, the visual field can respond with cones and rods at the same time. It is believed that this gives the elephant nose fish the ability to pick out predators moving quickly through its visual field.

Humans don’t have a tapetum lucidum, so when reflected light bounces off our retinas and back out the pupils, they appear red like the retinal blood vessels and tissues. This is the eerie red eye effect on some flash photography. I always thought it was a sign of vampirism!

Other nocturnal animals, like many owls, rely on hearing and smell more than vision. They are adapted to maximize these senses. We have discussed previously the changes in owl anatomy (Do You Have To Be Ugly To Hear Well) as examples of form following function to improve hearing. Other animals, like raccoons, have a heightened sense of touch. Their paws have elongated sensor pads, and thousands of touch receptors. With these, raccoons can differentiate textures well enough to tell if a fruit is ripe or not, even in the darkest night.

Raccoons have a strong sense of touch for moving around in the dark.

Their elongated paws have thousands of touch receptors to increase the

sensitivity of this sense. On the dorsal (back) side of the raccoon’s paw,

whiskers (vibrissae) on the ends of their digits heighten the sense of touch.

Raccoons don’t even have to touch something to sense it; they have vibrissae (whiskers) on the ends of their digits, above their claws. Whiskers in general are a potent aid to nocturnal animals, whether located on faces, paws, or bodies (remember the naked mole rat’s whiskers on its torso in Take Off Your Coat And Stay A While).

Even plants can be adapted for nocturnal activity. Moonflowers, night-blooming philodendrons, and other flowers that rely on nocturnal pollinators tend to be white (since their pollinators most likely can’t sense color), and strong smelling. Indeed, the increased temperature of the P. selloum spadix (Is It Hot In Here Or Is It Just My Philodendron) is an adaptation to nocturnality.

So why be nocturnal? Anyone who has tried to negotiate an unfamiliar room in the dark knows that being active in the dark brings certain obstacles that must be overcome. There must be distinct advantages to it or needs for it, or else nature wouldn’t go to the trouble of adapting. Some scientists believe that nocturnality arose from originally diurnal organisms taking advantage of an underused ecological niche. Being active at night can be a form of crypsis (hiding), either to make them better hunters, or to avoid being hunted.

Nocturnality can also reduce the amount of water lost to the environment, and can lower the thermal stress on certain species of animals. For example, many frogs lose water through their skin, so daylight and higher temperatures can dehydrate them quickly.

That doesn’t mean that certain species won’t be exceptions. Moths are all nocturnal, except for the polka-dotted wasp moth, that is. There are four species of wasp moths, all diurnal, but the polka-dot is the prettiest, so we will fall into that old trap and give the pretty one all the attention. Diurnally active, this moth has abandoned many of the nocturnal adaptations of its brethren.

The polka dot moth has color and patterns that might be useful

for mating or for warding off other animals, but they would

be wasted if the animal was nocturnal.

For instance, it is beautifully colorful, a no-no for nocturnal moths. Since color doesn’t show up at night, moths are generally white, tan, or grey. Second, the coloration, especially the bright rump, mimics a wasp (hence the name) and warns of a toxic mouthful if consumed. This defense is called aposematism (apo = away from, and soma = body, basically, keep away from me). Many brightly colored insects will make predators sick, purely a diurnal method of survival, as the warning colors would be of no use at night.

Just as this moth species is diurnal when its close relatives are nocturnal, there is a single genus of primate that has chosen to be nocturnal when all others, including humans, are diurnal. Owl monkeys (8 species) live in Central and South America, and leave their sleeping sites about 15 minutes after sunset each day. They forage for fruits and the odd flower or insect until just before sunrise, then retreat to a hollow tree or within dense foliage to sleep away the day.

Owl monkeys adopted a nocturnal pattern after millions of years being diurnal, so it must have afforded them some advantage or was an answer to some overwhelming stressor. They have adapted by developing larger eyes, with more rods and fewer cones. They still see color, but less so than other monkeys.

The owl monkey is nocturnal, so it needs to have more sensitive vision.

For this reason, it eyes (and eye sockets) are huge! Compare the eye

size and skull morphology in the diurnal capuchian monkey. Form of

the skull follows the functional capacity of the eye.

Owl monkeys are interesting to science for being the source of another exception, as they are the only primates susceptible to the human form of malaria. In The Perils of Plant Monogamy, we used malaria in chimps and humans as an example of divergent evolution; malaria developed into species-specific forms. But the owl monkey is susceptible to both the primate and human species, so they can substitute for humans in malaria research.

Malaria is caused by a parasite, and as such, depends on its host organism for nutrition. The rule is that parasites are active when their host is active (feeding). A good example is the intestinal parasite of the surgeonfish, E. fishelsoni (Of Fish Guts And Cancer).

As I am sure you have committed to memory and made a part of your life, E. fishelsoni grows to an amazing size and replicates its DNA thousands of times before it divides into two or three progeny organisms. It takes tremendous energy for a bacterium to grow 80 fold and produce 85,000 copies of its DNA in one day, so it must occur when nutrients and carbohydrates are plentiful - during the day when the fish is feeding. Although it is a stretch, I guess you could call E. fishelsoni a diurnal parasite.

The malaria parasite, Plasmodium falciparum, has chosen a different path. P. falciparum’s host is man, and man is diurnal (teenagers and third shift workers excepted), but the parasite works to produce many progeny (gametophytes) and have them mature in the nighttime. The reason is simple; malaria has two hosts.

Plasmodium falciparum needs two hosts to complete its life

cycle. One immature form (sporozoite from oocyst) grows

only in the mosquito, while another (gametocyte) forms only

from mature sporozoites in the human red blood cells.

While one stage of the organism grows in the human, another needs to be inside a mosquito in order to complete its life cycle. After finishing its development, it is ready to be injected into another human when the mosquito feeds again. The key is that the mosquito is nocturnal and the gametophyte is short-lived. The gametophyte must be produced and mature just in time to be sucked and deposited into the mosquito gut. P. falciparum has pressured to conform to the activity of one host while it is inside a host with the opposite activity pattern.

It is common that most species within a group will have similar activity patterns, since they are derived from common ancestors and therefore many characteristics are similar, including those that determine fitness for day life or nightlife. But there are exceptions. For instance, most rodents are nocturnal, but we see squirrels all day long - they are diurnal. Also, we mentioned above that most primates are diurnal, but the owl monkeys are nocturnal.

But there are bigger exceptions, organisms that aren’t diurnal or nocturnal. Ants, primates, and cats have species that are all over the place; some are nocturnal, some are diurnal and some are neither. It is the in-betweeners and the neithers that we will talk about next time.

Kreysing, M., Pusch, R., Haverkate, D., Landsberger, M., Engelmann, J., Ruiter, J., Mora-Ferrer, C., Ulbricht, E., Grosche, J., Franze, K., Streif, S., Schumacher, S., Makarov, F., Kacza, J., Guck, J., Wolburg, H., Bowmaker, J., von der Emde, G., Schuster, S., Wagner, H., Reichenbach, A., & Francke, M. (2012). Photonic Crystal Light Collectors in Fish Retina Improve Vision in Turbid Water Science, 336 (6089), 1700-1703 DOI: 10.1126/science.1218072

For more information or classroom activities on activity cycles, night vision or adaptation, see:

diurnal/nocturnal –

http://zoogirl-zootopia.blogspot.com/2010/08/nocturnal-diurnal-and-crepuscular.html

http://www.desertmuseum.org/kids/oz/long-fact-sheets/Title%20Page.php

http://www.bigfoothunting.com/info/bigfoot_nocturnal.shtml

http://www.mesacc.edu/dept/d10/asb/origins/primates/day_night.html

http://www.bbc.co.uk/learningzone/clips/different-adaptations-between-nocturnal-and-diurnal-animals/12644.html

http://www.brighthub.com/education/k-12/articles/58019.aspx

www.cal.org/siop/pdfs/nocturnal-vs-diurnal-animals-lesson.pdf

http://library.thinkquest.org/25553/english/interact/lessons/noctlp.shtml

www.seaworld.org/just-for-teachers/lsa/i-014/pdf/9-12.pdf

night vision –

http://www.pbs.org/wgbh/nova/kalahari/nightvision.html

http://dmohankumar.wordpress.com/2010/04/12/night-vision-in-animals/

http://www.news-medical.net/news/2009/04/16/48432.aspx

http://www.webexhibits.org/causesofcolor/17.html

http://www.bigbridge.org/BB14/NIGHT.HTM

http://animal.discovery.com/tv/night/

www.bouldercounty.org/play/recreation/naturedetectives/2004c.pdf

http://www.aoa.org/x6046.xml

http://www.aoa.org/x6035.xml

adaptation –

http://evolution.berkeley.edu/evosite/evo101/IIIE5Adaptation.shtml

https://notes.utk.edu/bio/greenberg.nsf/0/3ee9cccd7c64bffd85256cff0061f4d7?OpenDocument

http://www.nyu.edu/projects/fitch/courses/evolution/html/adaptation.html

http://news.nationalgeographic.com/news/2002/01/0110_020110TVfinches.html

http://www.pbs.org/wgbh/nova/teachers/resources/subj_06_03.html

http://www.nclark.net/Evolution

http://evolution.berkeley.edu/evolibrary/article/evo_31

http://ethemes.missouri.edu/themes/905

http://www.windows2universe.org/teacher_resources/teach_beaks.html

http://serc.carleton.edu/sp/mnstep/activities/35021.html

http://www.teachersdomain.org/resource/tdc02.sci.life.evo.lp_humanevo/

http://www.hhmi.org/biointeractive/activities/pocketmouse.html

http://www.teach-nology.com/teachers/lesson_plans/science/biology/evolution/

http://www.nationalgeographic.com/xpeditions/lessons/17/g35/smcreatecreature.html

The Best Cure for Insomnia Is To Get A Lot Of Sleep

Biology concepts – theories of sleep, REM sleep, circadian rhythms, neural plasticity

You open the door to your house and find your roommate sprawled out on the couch. Is he sleeping, unconscious, or dead? Knowing your roommate, you figure it could be any of them – you stop yourself short of naming a preference.

You find your roommate passed out in his underwear,

and can’t decide if he is sleeping, unconscious or dead.

If you have chosen Homer as a roommate, you have

already clued us in to your decision-making abilities.

The live/dead question is easy; hold a mirror under his nose and see if it fogs up. If he’s not breathing, there’s only one thing to do – go through his pockets and look for loose change (with a nod to “The Princess Bride”). But if you do see condensation, how do you decide if he is passed out or just sleeping - or are you considered unconscious when sleeping?

Sleep is voluntary, at least most of the time. I try to stay awake at the ballet, but I don’t always succeed. But besides drinking yourself into a stupor, going unconscious is usually not voluntary. Unfortunately (or fortunately), you weren’t there to see what preceded the crease marks on your roommate’s face or his drooling on the couch pillow, so how can you identify his state?

Sleeping implies that one has a diminished ability to respond to external stimuli with reduced sensory perception. However, unconsciousness appears much the same. The difference lies in the degree of diminished capacity; you can be roused more easily from sleep and perhaps not at all from deeper unconsciousness. Some people I know must pass out every night, because they are tough to wake up. You might parse the difference and just say that sleep is more easily rousable unconsciousness.

Sleep has stages and these stages have cycles. If deprived

of a particular stage the night before, your body will

change your cycles so that you make up the lost time in

that stage on the next night. Source for image: http://xavier

appsychology.wikispaces.com/Chapter+5,+ Period+6

A more profound difference between the two exists, but you won’t be able to detect it in your roommate without monitoring his brain waves. In sleep, you go through different phases, each with characteristic brain wave patterns. In 2007, a revised set of sleep stages was published, identifying 4 distinct phases, although stages 2 and 4 are repeated more than twice. Stage 4 is REM sleep, in which many many animals dream.

In general, the safer an animal is, the more it dreams. Predators dream more than prey and big species dream more than small species, though there are several exceptions to this rule. For example, ruminants (cows, deer, goats, and buffalo) dream very little (about 5 minutes/night), and cetaceans (whales, dolphins, porpoises) may not dream at all.

In contrast, animals that are born immature (not able to live on their own) tend to experience lots of REM sleep. These altricial (meaning “requiring nourishment") animals, including marsupials, cats, dogs, and most rodents, may have 6-8 hours of REM sleep a night. What is more, as adults they continue to dream heavily – about what, I have no idea.

Do you know the differences between dolphins and porpoises? Dolphins have longer bodies and snouts, and porpoises have a straight front edge on their dorsal fin. But, they are both cetaceans and have the same sleep patterns. Opposums, the only marsupials in North America, have immature young, and for some reason they dream much more. They are probably dreaming about the day their kids will get off their back.

But even this exception has an exception. Many birds are born very immature. They have no feathers, they can’t fly, they usually have their huge eyes closed, so they are definitely altricial species. But, birds have extremely short cycles of non-REM and REM sleep. Avian REM cycles might total only 5 minutes in a night, and each episode might be only 9 seconds long. What can you get done in a 9 second dream?

Brain waves recorded on an electroencephalogram

(EEG) show that dolphins and birds have normal

activity in one hemisphere while the other is at rest.

The heartbeat is constant showing that there is

normal body rhythm. This is unihemispheric sleep.

Image is taken from: Ridgeway, S. et. al. J. Exp. Med.

209:2902-2910, 2006.

REM sleep is deeper and harder to be roused from compared to non-REM sleep, the short cycles might be related to birds’ sleep pattern, which is unihemispheric (one half of the brain) in non-REM sleep, and is probably related to their need to keep watch for predators. Birds don’t lose muscle tone when they sleep; often they have to remain on a perch while they sleep. How embarrassing it would be for a bird to fall asleep and then fall off their branch- they would deserve to be eaten.

Other species of bird can sleep while flying, the arctic tern for example, whose migration can be as long as 22,000 miles one way. During flight, the eye connected the active half of the brain will remain open to navigate, but the bird will not dream, since both hemispheres are required in all animals for REM sleep.

Dreaming less doesn’t necessarily correlate with sleeping less. Animals that dream little may still sleep a considerable amount. For prey animals, sleep may represent a dicey time when they must be on the lookout. But it might also represent a way to stay motionless, blend in, and avoid predators. Either theory is practical, since predators seem to take the old, young, and diseased, whether sleeping or not.

Indisputably, every animal needs to sleep to survive, but why? It is interesting that science hasn’t quite figured this out yet. It is known that many beneficial events occur during sleep, but just being good for you doesn’t make them vital. But it must be vital, since even hibernating animals will cycle from hibernation to sleep in order to reap the benefits. Several theories exist for the necessity of sleep:

Energy conservation theory of sleep. Smaller animals carry less fat than large animals, which means they have a smaller margin of error in energy usage – they must conserve energy or feed more often. By sleeping longer, smaller animals keep their metabolic rate low and conserve more energy for when they need it, like for finding more food.

Related to this, animals with fewer predators seem to sleep longer than animals who may be hunted by many other species (as discussed above). However, since resting saves 90% as much energy as sleeping and that animals could watch for predators while resting, there clearly must be additional reasons to sleep instead of just rest.

Repair theory of sleep. This theory contends that non-REM sleep is important for repairing the physical body. Indeed, cell division and protein synthesis increase during non-REM sleep. On the other hand, REM sleep is necessary for restoring mental function, but we will leave the reasons for why we dream for another discussion.

Information packaging theory of sleep. You may sleep in order to provide the brain with time to process all that occurred the previous day, and be ready to take in more the next day. This relates to something called neural plasticity (new connections, ie. learning) and memory consolidation. Recent evidence shows that sleep deprivation harms recall, so sleep may help move information from short-term to long-term memory.

One theory of sleep is that your brain returns to a set

point so you can learn things the next day. Learning

means making new connections between neurons;

these connections are reinforced by neurotransmitters

being released to stimulate the next neuron in series. If

the neuron isn’t fired, it will not release neurotransmitters

to stimulate the next neuron in the path. If they are not

repeatedly fired, the pathway will no longer exist, and

new connections can be made.

In terms of plasticity, a 2007 study indicated that the slow brain waves in non-REM sleep are linked to our ability to learn new information. Dr. Guioli Tononi stated that neural connections become progressively weaker during slow wave sleep, so that by morning, the connections are ready to record new information, but still strong enough to hold the old memories.

An extension of this study, published in 2011 by the same group showed that in some groups of neurons, synapse size and number was affected by the amount of sleep that fly and the amount of experience that the fly had. More experience required more sleep in order to prune the connections and strengthen those that were used repeatedly. After a few hours of wake, synapse size and number increased, and sleep was required to reduce those that are weak and strengthen the remaining circuits.

If sleep provides all these benefits, and higher animals can’t survive without it (even insects and worms have periods of inactivity that look a lot like sleep), then how is it that the giraffe sleeps only 2-4 hours per day? As prey, nature may have deemed it more important to stay alert; or maybe they just can’t find a long enough blanket.

Cetaceans, like birds, only let half their brain sleep at a time, so they probably don’t dream either. Being mammals, they still have to be able to surface to inhale and exhale while sleeping, called conscious breathing. This might require that some part of their brain be active at all times.

I say might because most cetacean sleep studies have been done in captive animals (the smaller species). But in 2008, the boat of a cetacean research team accidentally floated into the middle of a pod of inactive sperm whales. The whales were unresponsive to the researchers and had both eyes closed. This agreed with another observation that electronically tagged sperm whales spent about 7% (1.68 hr/day) of their drifting with the tide. If this is true sleep (not unihemispheric), it would be a new finding in cetaceans and would indicate that that sperm whales sleep less than any other mammal.

The American bullfrog is fully alert when inactive, so is it

asleep? Scientists think that the bullfrog is so territorial and

is such a good parent that it will not let its guard down until

it dies.

An even more amazing exception to the sleep rule is the American bullfrog (Rana catesbeiana). Brain wave studies (electroencephalography) of the nocturnally active bullfrog did show signs of rest during the day, but bullfrogs had no loss of sensory perception. They could react to stimuli just as if awake. Other frogs show similar brain waves, but are much harder to arouse. The bullfrog might be the only animal to pull a lifetime all-nighter. He should really be ready for that math test.

Nobody yet knows exactly how sleep restores the brain or why bullfrogs and giraffes need so little, but we do know that people who are deprived of sleep suffer physically, emotionally, and intellectually – or worse. How would you like to be condemned to death for not taking a nap? We’ll talk about this next time.

Daniel Bushey, Giulio Tononi, Chiara Cirelli (2011). Sleep and Synaptic Homeostasis: Structural Evidence in Drosophila Science DOI: 10.1126/science.1202839

For more information, classroom activities, and laboratories on theories of sleep, and sleep in animals, see:

sleep –

http://www.ninds.nih.gov/disorders/brain_basics/understanding_sleep.htm

http://faculty.washington.edu/chudler/sleep.html

http://www.emedicinehealth.com/sleep_understanding_the_basics/article_em.htm

http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.0060216

http://www.whatislife.com/issues/issues-sleep.htm

http://www.pbs.org/wgbh/nova/teachers/activities/3410_01_nsn.html

http://faculty.washington.edu/chudler/experi.html

http://science.education.nih.gov/supplements/nih3/sleep/guide/using-lessons.htm

http://www.bioedonline.org/resources/nsbri.cfm

http://busyteacher.org/classroom_activities-vocabulary/sleep_and_dreaming-worksheets/

www.pbs.org/wgbh/nova/teachers/activities/pdf/3410_01_nsn.pdf

http://www.njdrivereducation.com/lessonplans

theories of sleep – http://psychology.about.com/od/statesofconsciousness/p/TheoriesofSleep.htm

http://www.macalester.edu/academics/psychology/whathap/ubnrp/dreaming/py4.html

http://www.livescience.com/10579-theory-questions-sleep.html

http://www.camden.rutgers.edu/~bwhitlow/Courses/Consciousness/POCdreamtheory/index.htm

http://cognitiveconvolutions.blogspot.com/2011/05/energetic-theories-of-sleep-function.html

stages of sleep and REM sleep –

http://www.webmd.com/sleep-disorders/excessive-sleepiness-10/sleep-101

http://www.ninds.nih.gov/disorders/brain_basics/understanding_sleep.htm

http://library.thinkquest.org/C005545/english/sleep/REM.htm

http://academic.pgcc.edu/~mhspear/sleep/stages/nrsleep.html

http://psychology.about.com/od/statesofconsciousness/a/SleepStages.htm

http://www.sleep.com/content/rem-sleep

http://web.mst.edu/~../userweb/psyworld/sleep_stages.htm

http://longevity.about.com/od/sleep/a/sleep_stages.htm

http://webspace.ship.edu/cgboer/genpsysleep.html

http://web.mst.edu/~../userweb/psyworld/sleep_stages.htm

sleep in animals –

http://library.thinkquest.org/25553/english/animals/index.shtml

http://faculty.washington.edu/chudler/chasleep.html

http://www.sleepfoundation.org/article/how-sleep-works/animals-sleep-there-human-connection

http://marinelife.about.com/od/marinelife101/tp/SleepInMarineAnimals.htm

http://www.madsci.org/posts/archives/2000-08/965504574.Zo.r.html

http://www.sleepeducation.com/howdoanimalssleep.aspx

http://www.newscientist.com/article/dn14164-why-brainy-animals-need-more-rem-sleep-after-all.html

http://www.apa.org/monitor/jan06/wild.aspx

http://thebrain.mcgill.ca/flash/capsules/outil_jaune07.html

Arctic Deer Can’t Dance - They’ve Lost Their Rhythm

Biology concepts – circadian rhythm, biological clock, periodicity, longevity

You get into bed but throw off the covers because you are hot. Hours later, you wake up shivering and go hunting for the discarded blanket. The temperature of the house has been the same all night, and your normal temperature is 98.6˚ F all the time, isn’t it? So why are your teeth chattering and toes blue?

I think I make my own circadian rhythms, because I don’t feel

my fastest reactions come after lunch… and how many

people feel strongest right after work?

Your body has circadian rhythms (circa = around or near, and diem = day), certain patterns that it repeats every day. Towards night, your pineal gland releases melatonin, which causes sleepiness. While you sleep, your brain lowers your blood pressure, slows your heart rate and yes, reduces your temperature about 1%. Towards morning, your heart rate and blood pressure increase, and your temperature returns to normal as you get ready for the activity of the day.

Mammalian circadian rhythms work to conserve energy and reduce the amount of food we must consume- if these things didn’t occur, we would all need to get up in the middle of the night for a snack, just to be sure we could get up the next morning. Conserving energy is a big thing for biological organisms; it can mean the difference between surviving and perishing in times of nutrient scarcity.

Circadian rhythms were first described in plants. In 1729, a mimosa plant (the sensitive plants that fold their leaves up when you touch them. Here is a video: http://www.youtube.com/watch?v=g0LFBM3hOLs) being brought back to Europe in the hold of a ship was noted to still have a daily turning of the leaves, as if they were following the sun.

Rhythms in plants control fruiting, leaf budding and falling, and flowering. Plant clocks can be reset by light, temperature, or nutrient levels, so that plants can keep up with the changing of the seasons. It is interesting that some plants flower based on the number of hours of sunlight per day, while others take their cues from number of hours of darkness. This can be important for commerical nurseries.

We have seen that there are rhythms that run on daily schedules, monthly schedules, or seasonal schedules. Many mechanisms must work together to control the periodicity of the numerous functions and timetables. This implies a fairly complex level of control. Take your own daily clock for instance. Human biological clocks run on a 24.2 hour cycle, not 24. So if you are remain somewhere that provides no time cues, say…… a Las Vegas casino, within a couple of weeks you will end up sleeping all day and staying up all night. And you’ll be poor.

However, the longer period is an advantage. If all animals were on the same clock, then they would all want to eat at the same time, which would make competition greater. Our primitive selves were happy to have a clock that was slightly longer and could be reset for different seasons and locations on Earth, it improved their chances at survival.

Neurons connecting your retina to your suprachiasmatic

nuclei reset your biological clock. Illuminescence is measured

in lux; it takes about 400 lux to affect your biological clock and

5000 lux to reset it, and a bathroom light at 2:00 am can put

out about 500 lux. Maybe you should use a nightlight. A sunny

day, by contrast, measures up out about 20,000 lux.

You reset your clock each day by being exposed to sunlight. Neural tracts run from your retinas to the superchiasmatic nuclei (super = above, chiasm = crossing of two tracts to form an X, nucleus = group of neuron endings with similar function) of the brain. The light signal reboots your clock and keeps you on a 24 hr cycle.

A temperature cycle can be related other functions as well. Women tend to increase their body temperature just after ovulation, so this is an infradian rhythm (longer than one day) working with a circadian rhythm. Your body is most susceptible to fever at night when your temperature is lowest (in a study of patients with low white blood cell counts). This may be a mechanism for allowing the healing aspects of febrile response (fever, the increased temperature can slow down or kill pathogens) while reducing the chance that a body-damaging temperature will be reached.

It turns out that lower core body temperatures may also have other benefits. A recent study indicated that people who live longer have lower core body temperatures (were the colder able to get older, or do you get colder as you get older? – we can’t tell from this study). However, a study in mice showed that a lower average core body temperature in young mice did result in living longer.

Is longer life really a blessing if you have to

starve yourself to get it?

How can you lower your normal body temperature? A 2010 study showed that long-term caloric restriction (1750 kCal/day) could lower core body temperature, and this was more important for longevity than was endurance exercise. Being colder means expending less energy, so less oxygen is needed, and therefore less oxidative damage is done (oxidative damage = aging). A recipe for living longer might be: don’t eat very much, sleep at least 10 hours/night, and stay calm. It is interesting how much control we can have on supposedly innate behaviors and natural outcomes.

Unfortunately, not all animals can make biological clock decisions for themselves. Some animal habitats don’t lend themselves to resetting clocks. Take arctic animals for example. For long periods of the year, there is either no day or no night. How can you hope to run a legitimate clock cycle under those conditions? Maybe there should be an exception to dependence on light cycles for clocks. Well, there is.

It turns out that arctic reindeer can turn their clocks off - sort of a biological snooze button. That way they can forage and nap, and forage and nap, not worrying about the time of day. No curfews for those teenagers! However, they must have some biologic sense of time, as they still mate and give birth in periods of relative food abundance.

Without an internal clock to rely on, does Santa have to keep

reminding Rudolph when its about to time to deliver presents?

So arctic reindeer may have no rhythm, and they live where there isn’t much food, so they are probably extending their lives by caloric restriction as well – more time for dance lessons.

The arctic and antarctic patterns definitely mess with human clock function. As humans, we are still slaves to our clocks and to light entraining of the daily rhythm. Seasonal affective disorder (SAD, affect = mood, it is like the winter blahs gone nuclear) is common in people who live in the far north, and is thought to be responsible for high suicide rates noted in winter, especially in people from Finland. Light therapy is helpful, whether by resetting clocks or by stimulating the production of vitamin D. I wonder if the arctic deer are depressed as well?

Other animals maintain circadian rhythms without light stimuli. A 2011 study indicates that blind cave fish from Somalia, Phreatichthys andruzzii, seem to have a 47 hour infradian clock. It is interesting to me that our clock is just a hair over one day, while the P. andruzzii clock is just a hair under two days and other animals have clocks near multiples of 24 – I have no idea what that might suggest – I just find it mathematically intriguing.

Cavefish have lost pigment as well as vision; neither

seem to matter much in a pitch black cave environment.

Scientists do not know what triggers may reset the P. andruzzii's clock, but the fish’s natural rhythm may be influenced by the patterns of its prey or predators. A reset based on food intake is not out of the question, as one is suspected in humans, but the molecular mechanism has not been identified.

We have seen that plants and animals (as wells fungi and bacteria) have daily rhythms that control physiology, behavior and mental processing, and we have seen that body temperature rhythm is important for mammalian survival. However, next time we will see that the vast majority of living things do not micromanage their temperature like we do, and they get along just fine.

For more information, classroom activities, or laboratories:

Circadian rhythm –

http://learn.genetics.utah.edu/content/begin/dna/clockgenes/

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Circadian.html

http://www.circadian.org/biorhyt.html

http://www.plantcell.org/content/18/4/792.full

http://bcs.whfreeman.com/thelifewire/content/chp52/5202002.html

http://web.mit.edu/newsoffice/2010/clockwork-bacteria-0319.html

http://news.bbc.co.uk/2/hi/science/nature/166363.stm

http://biology4.wustl.edu/faculty/herzog/BioTiming%20Tutorial/class.html

http://neuron.illinois.edu/curriculum/circadian.php

http://teachhealthk-12.uthscsa.edu/curriculum/sleep/sleep04c.asp