Why You Can’t Hibernate the Winter Away

A reposting of an original article from January, 2015.

You open your eyes, slap the alarm, and pull the covers a little tighter around your shoulders. It’s still dark outside and you dread the moment that you step out from under the warm comforter and the cold sucks your breath out. Can’t you just hibernate and sleep the winter away?

A dormouse in his snuggly hibernation state.
Image by Krysztof Dreszer at Wikimedia.

Actually, no. Hibernation and sleep are two completely different physiological processes (shown by studies of brain function). And chances are, you don’t have the physiological bits needed to hibernate safely.

Hibernation has more to do with energy and body temperature than it does with sleep. Hibernation is defined as a process in which an animal allows its body temperature to approximate the environmental temperature for several days or longer. It is a strategy that some animals use during periods of food shortage to conserve the energy that would normally be used to generate body heat. When food is scarce in the winter, the animal will lower its metabolism (the burning of food molecules to create energy and heat), which will result in the animal having less energy (and entering a sleep-like state) and less heat (until the body approaches the environmental temperature). So really, hibernation is the reduction of metabolism when food is scarce. Lack of activity and cold body temperatures are just the by-products.

Almost all species that hibernate are small mammals, including some hamsters, dormice, jumping mice, ground squirrels, marmots, woodchucks, bats, marsupials and monotremes. Bears, common examples of hibernating species, are actually debated by scientists as to whether they should even be considered hibernators due to the fact that their metabolisms and body temperatures do not decline as much as those of other hibernating species. The only bird species known to hibernate is the poorwill.

Each hibernating species has a specific range of body temperatures that their body can endure. Their first line of defense is to find a hibernaculum (a chamber or cavity in which to hibernate that is more insulated than the exposed environment). If the hibernaculum becomes so cold that the animal’s body temperature drops below its minimum endured range, it will either increase its metabolism slightly to raise its body temperature or it will arouse (wake up). Arousal is the process of increasing metabolic heat production to near-normal levels. All hibernating species seem to undergo multiple periods of temporary arousals during hibernation and scientists are still unsure why. Increasing the metabolism and body temperature from lower levels is an energetically costly process (similar to how your car uses more gas to accelerate than to maintain a higher speed). In most hibernating species, the process of increasing the metabolism uses a specialized tissue called brown fat.

Fat cells come in two main types: white fat and brown fat. White fat, the squishy stuff that we constantly try to diet and exercise away, is filled with lipids (fats) that we store to generate energy in the future. Brown fat cells also contains lipids, but they are specialized to break them down faster. Brown fat is found in newborn mammals and adult hibernators and is commonly located on the upper back, neck, chest and belly (like a vest) and around major arteries. Brown fat cells have lots of mitochondria (the metabolic parts of the cell that break down food molecules like lipids to generate energy). Brown fat mitochondria is specialized in that they have a protein called uncoupling protein 1 that causes them to generate heat rather than energy when they break down lipids. When the body becomes stressed, it releases norepinephrine, a stress hormone, which causes brown fat cells to increase the rate at which they break down lipids to generate heat. This heat warms the major arteries and increases blood flow, which then distributes the heat throughout the body.

A PET scan shows brown fat in a human.
Image by Hellerhoff at Wikimedia.

Although humans are born with a fair amount of brown fat, we lose it as we age. More specifically, it converts to white fat. We used to think that we lost it completely, but in recent years we have learned that some lean adults maintain a few pockets of brown fat in their necks and chests that obese people are more likely to lose. Researchers are currently exploring if and how we can convert some of our adult white fat to brown fat in order to increase our metabolisms and potentially combat obesity and diabetes.

So for now, we can’t hibernate the winter away. But continuing research into hibernating animals may hold an important secret to our own health.

Caught in My Web: Mind-Altering Substances

Image by Luc Viatour at Wikimedia Commons

Drunken birds have gone viral this week! For this edition of Caught in My Web, we wonder if animals alter their mental states like people do.

1. Drunk Minnesotan birds are flying into windows! At least that is what the viral story says. But the truth may be a bit more measured. As the Police Chief of Gilbert, Minnesota says, “It sounds like every bird in our town is hammered, and that’s not the case.” Read the real story here.

2. But do wild animals really drink alcohol? Not in the way that we do, maybe, but many consume overly fermented fruits. Some have developed a tolerance to the high alcohol content, others, not so much. Just ask this poor drunk moose that got herself stuck in a tree after eating too many fermented apples.

3. But it’s not just fermented fruits that get animals drunk. Some fish can make their own alcohol to help them survive a long winter under the ice.

4. What about the effects of other mind-altering substances on animals? Ever wonder what kind of web a spider would make on different drugs? In 1948, a zoologist at the University of Tubingen in Germany by the name of H.M. Peters did.

5. Octopuses are normally very solitary creatures… that is, unless they are given ecstasy. Apparently, even octopuses seek social interactions when they take the common party drug.

Freezing the Winter Away

An edited reposting of an article from January 8, 2014.

During this frigid winter we can be thankful for our home heating, our layers of warm clothing, and most of all, our bodies’ abilities to generate heat. But it is times like these that make me wonder about our friends that live outside year-round… especially those that don’t generate most of their own body heat. How do they survive these periods of intense cold? There are several species of North American frogs that have an unusual trick up their sleeve: They freeze nearly solid and still live to see the next spring.

This picture of a wood frog is by Ontley at Wikimedia Commons.

Frogs are ectothermic, meaning they take on the temperature of their surroundings rather than generate their own body heat. This introduces some intriguing questions about how these species even exist in northern climates that experience freezing temperatures every year. When various North American frog species (including wood frogs, spring peepers, western chorus frogs, and a few gray tree frog species) take on freezing winter temperatures, they actually allow their bodies to freeze nearly solid. For most species, this would be a deadly approach: a frozen circulatory system would halt the delivery of oxygen to cells, which require oxygen to generate the energy they need to do just about everything a cell does. Furthermore, jagged ice crystal edges could rupture the cells they are inside. Dead cells lead to dead organs, which in turn lead to dead animals. These freezing frogs have found the secrets to freezing without killing their cells.

The first secret of the freezing frogs is to spend the winter snuggled in the leaf litter below the snow. This environment insulates and protects the frogs from the deadly wind chills we have been facing for the last several days.

The second secret of the freezing frogs is a creative use of colligative properties. Colligative properties are properties of solutions that depend on the ratio of the number of liquid molecules to the number of molecules of stuff dissolved in that liquid. One of those properties is called freezing point depression: The temperature at which a liquid will freeze can be lowered by adding particles to it. (This is why salt is spread on roads in the winter). A critical component of the freezing frog strategy is for the liver to produce massive amounts of glucose in response to the start of freezing. This glucose is pumped throughout the body, which lowers the freezing point of all of the organs.

A third secret of the freezing frogs is the use of ice nucleating agents: proteins that actually encourage freezing. This may seem counterintuitive, but remember that ice crystals inside cells can cause them physical damage. By having a high concentration of ice nucleating agents in the fluid between the cells, this ensures that ice first forms in the spaces surrounding the cells. When ice forms, the ice crystals are made of only water molecules, which draws water out of the solution and leaves behind a higher concentration of other stuff (like glucose) in between the cells. The high concentration of glucose between the cells draws water out of the cells and into that space. This additional water also freezes. In the end, the cells are chock-full of particles, lowering their freezing temperature, and are surrounded by ice, which insulates the cells. Thus, this process of ice formation around the cells prevents ice from forming inside the cells.

A fourth secret of the freezing frogs is a metabolic shift. Most animal cells rely on oxygen to produce the energy they need to support their demands. But cells have ways of producing energy without oxygen too. These ways are not very efficient, but are useful when there is not enough oxygen available to meet demand (such as when a seal dives or a cheetah reaches burst speed). When freezing frogs start to freeze and oxygen delivery to the cells slows and eventually stops, their cells shift from an oxygen-reliant system of energy creation to an oxygen-independent system of energy creation. Additionally, freezing organs do less and don’t require as much energy anyway, so they can continue functioning at low levels for a long time if the freezing spell is prolonged.

When the environment warms up (as forecasters promise will happen), the body temperatures of these frogs raise and body fluids slowly become liquid again. The heart starts to beat again within hours of the start of thawing and oxygen can again be delivered around the body. The delivery of oxygen-carrying blood helps the rest of the organs return to their normal functions.

There are still many secrets of these freezing frogs left to uncover. Maybe you’ll be the one to do it… once we thaw out a bit.

Want to know more? Check these out:

1. Storey, K.B. (2004). Strategies for exploration of freeze responsive gene expression: advances in vertebrate freeze tolerance Cryobiology, 48, 134-145 DOI: 10.1016/j.cryobiol.2003.10.008

2. Layne, J.R., & Lee, R.E. (1995). Adaptations of frogs to survive freezing Climate Research, 5, 53-59 DOI: 10.3354/cr005053

The Truth Behind Those Sleeping Bears (A Guest Post)

A reposting of an article by Tabitha Starjnski-Schneider on December 8, 2014.

Name some animals that hibernate.

Was the first one mentioned a bear? That’s understandable…you were probably told that bears go to sleep shortly before winter, stay asleep the entire winter, and wake up in early spring.

What if I told you that your teachers lied to you, and that bears don’t actually hibernate?! Not a true hibernation, at least.

For an animal to be considered a true hibernator, it actually needs to stay in a sleep state for months at a time (like during an entire season), but also lower its body temperature far below where most other animals barely survive. Such an animal thus hibernates by lowering its metabolism, dropping its body temperature, and passing, most commonly, much of the winter in this Rip Van Winkle state. The many challenges of enduring a long and strenuous season such as winter, while "sleeping" it away, are complicated, but here we talk about just a couple.

Something your teacher may have also told you was that bears are mammals, and therefore are "warm-blooded". That seems a little silly; all animals with blood are going to have warm blood. Bears are actually called endothermic, meaning they don’t have to rely on warming or cooling their bodies by outside forces such as the sun. While undergoing this sleep-state, bears possess internal and external temperature control. These animals slightly lower their heart rate and body temperature internally and minimize their external movements in an effort to save energy and conserve heat. Of course these periods of reduced heart rate, temperature and inactivity don’t actually last all winter, as with true hibernation, but only a few weeks at a time. This overall ability and state is called torpor, not true hibernation. And although there is debate over the definitions of each, most researchers believe there is enough of a difference to categorize them separately (like cat naps versus comas).

One of the reasons for taking these naps is as basic as why we grocery shop. When the environment changes in such a way that doesn’t suit an animal (i.e. an empty fridge), they can better survive by conserving energy and going inactive until food returns. Before napping however, each adult bear will begin to dig a den, hollow out a tree trunk, and/or find a cave to prepare for winter. Once tucked away in their little beds, they use these dens like a Thermos, retaining as much of their body heat as possible. For the most part, these giants go to sleep for a few weeks at a time, wake up to warm their bodies some, then fall back asleep. This occurs over the course of a winter season until spring arrives and the bear can reemerge into the re-warmed world outside.

There is another, more important reason why these bears slumber though. After breeding in spring/summer, these mammals begin their fall-time buffet, eating foods high in carbohydrates and fat to gain as much weight as possible. Why you ask? So that the mothers gain enough fat and energy to develop, birth, and feed their young while in the winter hideaways. Ever see the videos of polar bears emerging with their cubs from a snowy fortress in the side of a hill?

Now how could they ever give birth if they were sleeping the whole time? It’s the same with black bears and grizzly bears, for that matter.

It all sounds pretty cool right? These mama bears should be given a medal for their dedication. And the next time someone refers to bears hibernating, you can assuredly respond that they actually enter a state of torpor, or winter-long cat naps.

The Weirdest Animals on Earth: 12 Amazing Facts About Platypuses

What IS that? A photo by Stefan Kraft at Wikimedia Commons.

1. Platypuses are so strange, that when British scientists first encountered one, they thought it was a joke: A Governor of New South Wales, Australia, sent a platypus pelt and sketch to British scientists in 1798. Even in their first published scientific description of the species, biologists thought that this duck-beaked, beaver-bodied, web-footed specimen may be some Frankenstein-like creation stitched together as a hoax. But this is only the beginning of their oddities…

2. Platypuses are egg-laying mammals. Mammals are animals that have a backbone, are warm-blooded, and females produce milk for their young. Most females that nurse their young also carry their developing babies in their bodies and give birth to live young… But platypuses don’t play by those rules. Platypuses are monotremes, egg-laying mammals that include the platypus and four species of echidna. Most female mammals have two functional ovaries, but female platypuses, like most female birds, only have a functional left ovary. Once a year, a female platypus may produce a clutch of two or three small, leathery eggs (similar to reptile eggs), that develop in her uterus for 28 days. Because female platypuses don’t even have a vagina, when the eggs are ready, she lays them through her cloaca, an opening that serves for reproduction, peeing and pooping. (In fact, monotreme comes from the Greek for “one hole”). She then curls around them and incubates them for another 10 days until they hatch.

3. Platypuses sweat milk! Not only do female platypuses not have vaginas, they don’t have nipples either! Instead, lactating mothers ooze milk from pores in their skin, which pools in grooves on their bellies so the babies can lap it up. …And they’re not even embarrassed about it!

4. Adult platypuses are toothless. Baby platypuses (that is the actual technical term for them, by the way… not “puggles”, which would be way more fun) are born with teeth but they lose them around the time that they leave the breeding burrow. In their place are rigid-edged keratinized pads that they use as grinding plates. When they catch their prey (worms, bugs, shrimp, and even crayfish), they store it in their cheek pouches and carry it to the surface, where they use gravel to crush it in their toothless maw.

5. The platypus “duck bill” is a sensory organ used to detect electric fields. Muscles and neurons use electrical impulses to function, and these impulses can be detected by electroreceptors. Although common in shark and ray species, electroreception is rare in mammals, only having been discovered in monotremes and the Guiana dolphin. Platypuses have rows of around 40,000 electroreceptors on their highly sensitive bill, which they wave back and forth in the water, much like a hammerhead shark, to determine the location of their prey. It’s a good thing this sense is so sensitive, since they close their eyes, nose and ears every time they dive.

6. Platypuses don’t use their tails like beavers do. Whereas beavers use their large, flat, leathery tails for swimming and slapping the water to send signals, platypuses don’t use their tails for any of that. Platypuses have large, flat tails for storing fat in case of a food shortage. Unlike beaver tails, platypus tails are covered in fur, which the mothers use to snuggle with their incubating eggs.

A platypus ankle spur. Photo by E.Lonnon at Wikimedia Commons.

7. Male platypuses have venomous ankle spurs. Their venom is strong enough to kill small animals and to create excruciating pain in humans. Since only males have it and they produce more venom during the breeding season, we think its main function may be to compete for mates and breeding territories.

8. Platypuses are knuckle-walkers with a reptilian gait. Although they are well-built for swimming with their webbed feet and legs on the sides of their bodies, these traits make it quite awkward to get around on dry land. To walk, they pull in their webbing and walk on their knuckles, exposing their claws. Like reptiles and salamanders, platypuses flex their spines from side-to-side, supported by their sprawling legs.

9. Platypuses have unusually low body temperatures. As unusual as they are, platypuses are still mammals, which are defined, in part, by their ability to generate most of their own body heat with their metabolism. Platypuses do this as well, but whereas most mammals maintain body temperatures between 37-40 degrees C (99-104 degrees F), platypuses are happy with a body temperature of 32 degrees C (90 degrees F). This lower metabolism reduces the amount of calories they need to eat.

10. They have no stomach. Stomachs are specialized protein-digesting chambers of digestive tracts that contain protein-digesting enzymes and acids to activate them. Not all animals have them, but most carnivores do. The most common exceptions to this rule are fish… and platypuses. Why? We don’t know for sure, but many of these animals consume diets high in calcium carbonate, which is a natural antacid. If their own diet would constantly neutralize their stomach acid, then the stomach really isn’t going to do them any good anyway.

11. They have 10 sex chromosomes! Most mammals have two sex chromosomes, one from each parent. An individual that has two X chromosomes is usually female and an individual that has one X and one Y chromosome is usually male. Thus, female mammals pass along an X chromosome to each offspring and males can pass along an X or a Y. But platypuses are not content to be normal in any way…They have 10 sex chromosomes: 5 from mom and 5 from dad. All 5 chromosomes from mom are Xs, whereas a male sperm either contains 5 Xs or 5 Ys. Birds also have two sex chromosomes, but in birds, individuals with two of the same type are usually male and individuals with different chromosomes are usually female. Their system is called ZW, where the mammalian system is XY. The platypus X chromosome is more similar than the X chromosome of other mammals to the bird Z chromosome.

12. The platypus genome is as much of a hodgepodge as its body. Only 80% of the platypus’ genes are like other mammals. Some of their genes have only previously been found in birds, reptiles, fish, or amphibians.

To learn about more weird animals, go here.

References:

Scheich, H., Langner, G., Tidemann, C., Coles, R., & Guppy, A. (1986). Electroreception and electrolocation in platypus Nature, 319 (6052), 401-402 DOI: 10.1038/319401a0

Warren, W., Hillier, L., Marshall Graves, J., Birney, E., Ponting, C., Grützner, F., Belov, K., Miller, W., Clarke, L., Chinwalla, A., Yang, S., Heger, A., Locke, D., Miethke, P., Waters, P., Veyrunes, F., Fulton, L., Fulton, B., Graves, T., Wallis, J., Puente, X., López-Otín, C., Ordóñez, G., Eichler, E., Chen, L., Cheng, Z., Deakin, J., Alsop, A., Thompson, K., Kirby, P., Papenfuss, A., Wakefield, M., Olender, T., Lancet, D., Huttley, G., Smit, A., Pask, A., Temple-Smith, P., Batzer, M., Walker, J., Konkel, M., Harris, R., Whittington, C., Wong, E., Gemmell, N., Buschiazzo, E., Vargas Jentzsch, I., Merkel, A., Schmitz, J., Zemann, A., Churakov, G., Ole Kriegs, J., Brosius, J., Murchison, E., Sachidanandam, R., Smith, C., Hannon, G., Tsend-Ayush, E., McMillan, D., Attenborough, R., Rens, W., Ferguson-Smith, M., Lefèvre, C., Sharp, J., Nicholas, K., Ray, D., Kube, M., Reinhardt, R., Pringle, T., Taylor, J., Jones, R., Nixon, B., Dacheux, J., Niwa, H., Sekita, Y., Huang, X., Stark, A., Kheradpour, P., Kellis, M., Flicek, P., Chen, Y., Webber, C., Hardison, R., Nelson, J., Hallsworth-Pepin, K., Delehaunty, K., Markovic, C., Minx, P., Feng, Y., Kremitzki, C., Mitreva, M., Glasscock, J., Wylie, T., Wohldmann, P., Thiru, P., Nhan, M., Pohl, C., Smith, S., Hou, S., Renfree, M., Mardis, E., & Wilson, R. (2008). Genome analysis of the platypus reveals unique signatures of evolution Nature, 453 (7192), 175-183 DOI: 10.1038/nature06936

A True Underdog…or Undermouse (A Guest Post)

By Spencer Henkel

People love a good underdog story, and nowhere is that image more embodied than in the rodents that live in deserts. In the desert there are two main problems that animals must face: it is way too hot and way too dry. You would think that rodents, the smallest of mammals, would not have much difficulty surviving in this kind of habitat. You might think that they would need far less food and water than their larger neighbors like reptiles and birds. Unfortunately, this is not the case; in fact, rodents’ small size actually makes life harder for them in such harsh conditions. Rodents gain and lose body heat faster through surface exchange with their environment, their highly active lifestyle requires a lot of food and a high metabolism, which generates a lot of extra heat that must be dispersed, and the distance they can travel to find food and water is extremely limited. Desert rodents must find ways to deal with all these issues, a tremendous feat for such tiny creatures.


Photo of a Golden Spiny Mouse (Acomys russatus) in Israel
by Mickey Samuni-Blank at Wikimedia Commons.

The most pressing concern of any animal that lives in the desert is making sure its body has enough water to carry it through the day. Needless to say, water can be hard to come by in such arid lands, and what water is present is usually found in seeds, tubers, and other plant material. Rodents will find and take in this water, but they face another problem: the contents of their diet are very salty. The rodents must now find a way to get rid of this excess salt while still holding onto a fair amount of water, for they cannot afford to simply excrete a steady stream of urine like we can. They must call upon a chemical from their brain, vasopressin, to help them out with this process. Vasopressin is an antidiuretic hormone, what I like to call an “anti-makes-you-pee”. It is made in the hypothalamus part of the brain, and when called upon it exits the pituitary gland and travels by blood to the kidneys. Once there, vasopressin causes the tiny blood vessels in the kidneys to clench up, slowing the flow of blood and increasing the time water has to be reabsorbed before urine is produced. When Nature eventually does call, the rodents will have made a small amount of urine that rids them of a whole lot of salt.

Now the rodents must turn to the other issue at hand: keeping cool. Water plays an active role in cooling an animal’s body by evaporation through sweating, panting, urinating, and defecating. Unfortunately, as with the salt in their diet, rodents can’t afford to lose all that water if they want their insides to keep functioning. So instead, rodents will lower their metabolisms. This reduces the amount of heat generated inside the body, so their core temperatures will decrease. A lower metabolism will also reduce the amount of water the rodents need to cool themselves down. However, if this process keeps up, the animal could die of hypothermia, ironically. So to keep that from happening, these rodents increase the amount of heat generated by their brown fat, masses of fat found primarily in animals that hibernate. This tissue will keep the animal’s core body temperature stable even when their metabolism slows way down.

In spite of their size, rodents actually have a rather tough time surviving in the desert. Yet they have found efficient ways of dealing with such extreme challenges. They can conserve enough water to live while still filtering out a great deal of salt, and they can slow down their own heat production while maintaining stable body temperatures. It is indeed quite a feat when the smallest of mammals succeeds in living in one of the harshest places on earth!

Sources Cited

SCHWIMMER, H., & HAIM, A. (2009). Physiological adaptations of small mammals to desert ecosystems Integrative Zoology, 4 (4), 357-366 DOI: 10.1111/j.1749-4877.2009.00176.x

This Animal Looks Like a Penis With Teeth... But It's Even Stranger Than That

This is a naked mole rat.

Yes, this is arguably the freakiest-looking animal on Earth.
Photo by Roman Klementschitz at Wikimedia Commons.

Naked mole rats are rodents that live in underground tunnels under East African savannas and grasslands. There's nothing all that strange about that... but how they have adapted to this lifestyle is unique... and, quite frankly, amazing.

For one thing, to cope with the low oxygen levels of the subterranean environment, naked mole rats have very low metabolisms and breathing rates. One of the biggest uses of metabolic engines in mammals is to produce our own body heat. These little guys have cut this big expenditure by being what may be the only ectothermic mammals on the planet. Ectotherms are animals like most fish, amphibians and reptiles that get most of their body heat from their environment, rather than making it themselves. Because naked mole rats want to exchange heat with their environment, they want to eliminate insulation... giving them their hairless and fatless bodies. Now when they bask in the sun at their tunnel entrances or huddle with their family they can take in all that warmth without anything getting in the way.

There are some benefits to having low metabolisms and not using much oxygen: Naked mole rats live for nearly 30 years (compared to 1-3 years in regular rats). Oxygen creates free radicals, highly reactive chemicals that cause damage to DNA, leading to a wide range of diseases. Naked mole rats don't just use less oxygen, but they have special proteins that are resistant to these damaging chemicals. They also produce a specialized super-sugar that has essentially eliminated cancer in this long-living species. What's more, these elderly rodents have managed to avoid dementia and osteoporosis, traits we hope to learn more about through ongoing research.

Naked mole rats have also developed some unique sensory traits. Living with your entire extended family in underground burrows means that you live in high levels of carbon dioxide and walls saturated in pee. These little guys don't even have any body hair to protect their pink skin from all that burning ammonia. Their solution: get rid of pain. These guys have no pain receptors for noxious chemicals like acids or capsaicin (the stuff that makes hot peppers hot). Furthermore, they are lacking a specific neurotransmitter, called substance P, that other mammals use to send many pain signals. Since naked mole rats have less need for sensation in their skin, they have developed brains that have repurposed about 30% of the sematosensory cortex (the part of the brain that interprets touch sensations) to their digging teeth!

Perhaps the strangest quality of all for these animals is their behavior. Naked mole rats are one of only two known mammals that are eusocial (the other being the Damaraland mole rat). Eusociality is a social organization common among bees, wasps, ants and termites, in which the colony has castes that include queens, workers and soldiers. Among naked mole rats, there is a single queen in the colony that mates with a few dominant males; workers that dig the tunnels, gather food, and care for the young; and soldiers that protect the colony from predators. Workers and soldiers are all reproductively sterile with undeveloped gonads and low hormone levels. However, if the queen dies, one of the non-reproducing females will go through puberty and take on her role as the new queen.

Now that you know that naked mole rats are so much more than just a "freaky thing", enjoy this naked mole rat rap (or maybe even a whole episode of Disney's Kim Possible, which features Rufus, the naked mole rat):

How Fungus Makes Ant Zombies

"Ants biting the underside of leaves as a result of infection
by O. unilateralis. The top panel shows the whole leaf with
the dense surrounding vegetation in the background and the
lower panel shows a close up view of dead ant attached to
a leaf vein. The stroma of the fungus emerges from the back
of the ant's head and the perithecia, from which spores are
produced, grows from one side of this stroma, hence the
species epithet. The photograph has been rotated
to aid visualization." Image and caption by David P. Hughes
and Maj-Britt Pontoppidan at Wikimedia Commons.

The parasitic fungus, Ophiocordyceps unilateralis sensu latu (O. unilateralis, for short), infects the brains of Carpenter ants, turning them into zombies that live and die for the sole purpose of helping the fungus thrive and reproduce. Under the influence of the fungus, zombie Carpenter ants leave their nests at an odd yet specific time, move randomly and convulsively, and climb up the north side of a plant to almost exactly 25 cm, where they bite the leaf vein. Once they bite the leaf, the muscles of their mandibles (mouth parts) deteriorate, causing lockjaw and fixing the ant victim in place while its legs kick and twitch. After a few hours, the movement stops as the fungus kills the ant, continues to grow throughout the victim's head, and then sprouts out of the back of the head. The fungus anchors itself to the plant and releases antimicrobial chemicals to protect itself and grows fruiting bodies from the ant's head to release its spores, spawning the next generation of fungus. O. unilateralis has been known to infect and wipe out entire Carpenter ant colonies, leaving dense aerial graveyards of ant carcasses in its wake.

Today at Accumulating Glitches, I talk about new research that has used genetic techniques to determine how this parasitic fungus takes over the minds of its ant victims. Check it out here.

And to learn more, check this out:

de Bekker, C., Ohm, R.A., Loreto, R.G., Sebastian, A., Albert, I., Merrow, M., Brachmann, A. and Hughes, D.P. Gene expression during zombie ant biting behavior reflects the complexity underlying fungal parasitic behavioral manipulation, BMC Genomics, 16:620, 1-23 (2015). DOI 10.1186/s12864-015-1812-x.

Why You Can’t Hibernate the Winter Away

You open your eyes, slap the alarm, and pull the covers a little tighter around your shoulders. It’s still dark outside and you dread the moment that you step out from under the warm comforter and the cold sucks your breath out. Can’t you just hibernate and sleep the winter away?

A dormouse in his snuggly hibernation state.
Image by Krysztof Dreszer at Wikimedia.

Actually, no. Hibernation and sleep are two completely different physiological processes (shown by studies of brain function). And chances are, you don’t have the physiological bits needed to hibernate safely.

Hibernation has more to do with energy and body temperature than it does with sleep. Hibernation is defined as a process in which an animal allows its body temperature to approximate the environmental temperature for several days or longer. It is a strategy that some animals use during periods of food shortage to conserve the energy that would normally be used to generate body heat. When food is scarce in the winter, the animal will lower its metabolism (the burning of food molecules to create energy and heat), which will result in the animal having less energy (and entering a sleep-like state) and less heat (until the body approaches the environmental temperature). So really, hibernation is the reduction of metabolism when food is scarce. Lack of activity and cold body temperatures are just the by-products.

Almost all species that hibernate are small mammals, including some hamsters, dormice, jumping mice, ground squirrels, marmots, woodchucks, bats, marsupials and monotremes. Bears, common examples of hibernating species, are actually debated by scientists as to whether they should even be considered hibernators due to the fact that their metabolisms and body temperatures do not decline as much as those of other hibernating species. The only bird species known to hibernate is the poorwill.

Each hibernating species has a specific range of body temperatures that their body can endure. Their first line of defense is to find a hibernaculum (a chamber or cavity in which to hibernate that is more insulated than the exposed environment). If the hibernaculum becomes so cold that the animal’s body temperature drops below its minimum endured range, it will either increase its metabolism slightly to raise its body temperature or it will arouse (wake up). Arousal is the process of increasing metabolic heat production to near-normal levels. All hibernating species seem to undergo multiple periods of temporary arousals during hibernation and scientists are still unsure why. Increasing the metabolism and body temperature from lower levels is an energetically costly process (similar to how your car uses more gas to accelerate than to maintain a higher speed). In most hibernating species, the process of increasing the metabolism uses a specialized tissue called brown fat.

Fat cells come in two main types: white fat and brown fat. White fat, the squishy stuff that we constantly try to diet and exercise away, is filled with lipids (fats) that we store to generate energy in the future. Brown fat cells also contains lipids, but they are specialized to break them down faster. Brown fat is found in newborn mammals and adult hibernators and is commonly located on the upper back, neck, chest and belly (like a vest) and around major arteries. Brown fat cells have lots of mitochondria (the metabolic parts of the cell that break down food molecules like lipids to generate energy). Brown fat mitochondria is specialized in that they have a protein called uncoupling protein 1 that causes them to generate heat rather than energy when they break down lipids. When the body becomes stressed, it releases norepinephrine, a stress hormone, which causes brown fat cells to increase the rate at which they break down lipids to generate heat. This heat warms the major arteries and increases blood flow, which then distributes the heat throughout the body.

A PET scan shows brown fat in a human.
Image by Hellerhoff at Wikimedia.

Although humans are born with a fair amount of brown fat, we lose it as we age. More specifically, it converts to white fat. We used to think that we lost it completely, but in recent years we have learned that some lean adults maintain a few pockets of brown fat in their necks and chests that obese people are more likely to lose. Researchers are currently exploring if and how we can convert some of our adult white fat to brown fat in order to increase our metabolisms and potentially combat obesity and diabetes.

So for now, we can’t hibernate the winter away. But continuing research into hibernating animals may hold an important secret to our own health.

The Truth Behind Those Sleeping Bears (A Guest Post)

By Tabitha Starjnski-Schneider

Name some animals that hibernate.

Was the first one mentioned a bear? That’s understandable…you were probably told that bears go to sleep shortly before winter, stay asleep the entire winter, and wake up in early spring.

What if I told you that your teachers lied to you, and that bears don’t actually hibernate?! Not a true hibernation, at least.

For an animal to be considered a true hibernator, it actually needs to stay in a sleep state for months at a time (like during an entire season), but also lower its body temperature far below where most other animals barely survive. Such an animal thus hibernates by lowering its metabolism, dropping its body temperature, and passing, most commonly, much of the winter in this Rip Van Winkle state. The many challenges of enduring a long and strenuous season such as winter, while "sleeping" it away, are complicated, but here we talk about just a couple.

Something your teacher may have also told you was that bears are mammals, and therefore are "warm-blooded". That seems a little silly; all animals with blood are going to have warm blood. Bears are actually called endothermic, meaning they don’t have to rely on warming or cooling their bodies by outside forces such as the sun. While undergoing this sleep-state, bears possess internal and external temperature control. These animals slightly lower their heart rate and body temperature internally and minimize their external movements in an effort to save energy and conserve heat. Of course these periods of reduced heart rate, temperature and inactivity don’t actually last all winter, as with true hibernation, but only a few weeks at a time. This overall ability and state is called torpor, not true hibernation. And although there is debate over the definitions of each, most researchers believe there is enough of a difference to categorize them separately (like cat naps versus comas).

One of the reasons for taking these naps is as basic as why we grocery shop. When the environment changes in such a way that doesn’t suit an animal (i.e. an empty fridge), they can better survive by conserving energy and going inactive until food returns. Before napping however, each adult bear will begin to dig a den, hollow out a tree trunk, and/or find a cave to prepare for winter. Once tucked away in their little beds, they use these dens like a Thermos, retaining as much of their body heat as possible. For the most part, these giants go to sleep for a few weeks at a time, wake up to warm their bodies some, then fall back asleep. This occurs over the course of a winter season until spring arrives and the bear can reemerge into the re-warmed world outside.

There is another, more important reason why these bears slumber though. After breeding in spring/summer, these mammals begin their fall-time buffet, eating foods high in carbohydrates and fat to gain as much weight as possible. Why you ask? So that the mothers gain enough fat and energy to develop, birth, and feed their young while in the winter hideaways. Ever see the videos of polar bears emerging with their cubs from a snowy fortress in the side of a hill?

Now how could they ever give birth if they were sleeping the whole time? It’s the same with black bears and grizzly bears, for that matter.

It all sounds pretty cool right? These mama bears should be given a medal for their dedication. And the next time someone refers to bears hibernating, you can assuredly respond that they actually enter a state of torpor, or winter-long cat naps.

Freezing the Winter Away

The clutches of the Polar Vortex are finally releasing its grasp on us and we can be thankful for our home heating, our layers of warm clothing, and most of all, our bodies’ abilities to generate heat. But it is times like these that make me wonder about our friends that live outside year-round… especially those that don’t generate most of their own body heat. How do they survive these periods of intense cold? There are several species of North American frogs that have an unusual trick up their sleeve: They freeze nearly solid and still live to see the next spring.

This picture of a wood frog is by Ontley at Wikimedia Commons.

Frogs are ectothermic, meaning they take on the temperature of their surroundings rather than generate their own body heat. This introduces some intriguing questions about how these species even exist in northern climates that experience freezing temperatures every year. When various North American frog species (including wood frogs, spring peepers, western chorus frogs, and a few gray tree frog species) take on freezing winter temperatures, they actually allow their bodies to freeze nearly solid. For most species, this would be a deadly approach: a frozen circulatory system would halt the delivery of oxygen to cells, which require oxygen to generate the energy they need to do just about everything a cell does. Furthermore, jagged ice crystal edges could rupture the cells they are inside. Dead cells lead to dead organs, which in turn lead to dead animals. These freezing frogs have found the secrets to freezing without killing their cells.

The first secret of the freezing frogs is to spend the winter snuggled in the leaf litter below the snow. This environment insulates and protects the frogs from the deadly wind chills we have been facing for the last several days.

The second secret of the freezing frogs is a creative use of colligative properties. Colligative properties are properties of solutions that depend on the ratio of the number of liquid molecules to the number of molecules of stuff dissolved in that liquid. One of those properties is called freezing point depression: The temperature at which a liquid will freeze can be lowered by adding particles to it. (This is why salt is spread on roads in the winter). A critical component of the freezing frog strategy is for the liver to produce massive amounts of glucose in response to the start of freezing. This glucose is pumped throughout the body, which lowers the freezing point of all of the organs.

A third secret of the freezing frogs is the use of ice nucleating agents: proteins that actually encourage freezing. This may seem counterintuitive, but remember that ice crystals inside cells can cause them physical damage. By having a high concentration of ice nucleating agents in the fluid between the cells, this ensures that ice first forms in the spaces surrounding the cells. When ice forms, the ice crystals are made of only water molecules, which draws water out of the solution and leaves behind a higher concentration of other stuff (like glucose) in between the cells. The high concentration of glucose between the cells draws water out of the cells and into that space. This additional water also freezes. In the end, the cells are chock-full of particles, lowering their freezing temperature, and are surrounded by ice, which insulates the cells. Thus, this process of ice formation around the cells prevents ice from forming inside the cells.

A fourth secret of the freezing frogs is a metabolic shift. Most animal cells rely on oxygen to produce the energy they need to support their demands. But cells have ways of producing energy without oxygen too. These ways are not very efficient, but are useful when there is not enough oxygen available to meet demand (such as when a seal dives or a cheetah reaches burst speed). When freezing frogs start to freeze and oxygen delivery to the cells slows and eventually stops, their cells shift from an oxygen-reliant system of energy creation to an oxygen-independent system of energy creation. Additionally, freezing organs do less and don’t require as much energy anyway, so they can continue functioning at low levels for a long time if the freezing spell is prolonged.

When the environment warms up (as forecasters promise will happen), the body temperatures of these frogs raise and body fluids slowly become liquid again. The heart starts to beat again within hours of the start of thawing and oxygen can again be delivered around the body. The delivery of oxygen-carrying blood helps the rest of the organs return to their normal functions.

There are still many secrets of these freezing frogs left to uncover. Maybe you’ll be the one to do it… once we thaw out a bit.

Want to know more? Check these out:

1. Storey, K.B. (2004). Strategies for exploration of freeze responsive gene expression: advances in vertebrate freeze tolerance Cryobiology, 48, 134-145 DOI: 10.1016/j.cryobiol.2003.10.008

2. Layne, J.R., & Lee, R.E. (1995). Adaptations of frogs to survive freezing Climate Research, 5, 53-59 DOI: 10.3354/cr005053

Metabolism and Body Size Influence the Perception of Movement and Time

Zoetropes like this one have been used
for almost 2000 years. If you look in the
slits from the side, the image appears to
be animated. Image by Andrew Dunn
at Wikimedia Commons.

When we watch TV or a movie, we are essentially watching a series of still images presented in rapid succession… so rapid, in fact, that we perceive them to be a single moving image. The ability of movie-makers to convince us that still images are fluid in time is based on our physiology. Specifically, moving-pictures, as they were once called, rely on our critical flicker fusion frequency (CFF), the lowest speed at which we perceive a flashing light source to be a constant light. But we don't have our CFF so we can enjoy movies and TV; it came about from our need to identify and track moving objects.

The ability to identify and track moving objects is critically important for finding and catching prey, avoiding predators, and finding mates. It is these visual abilities that rely on an animal’s CFF. An animal with a low CFF will miss many visual details, like watching your TV with a fast-forward function that jumps ahead 15 seconds at a time. An animal with a high CFF will see all the details that happen in between with a fine-time-scale resolution. But if having a high CFF conveys such an advantage, why don’t all animals have a high CFF?

This week at Accumulating Glitches I talk about how an animal's size and metabolism can influence how it sees the world. Check it out here.

And to learn more, check this out:

Healy, K., McNally, L., Ruxton, G.D., Cooper, N., & Jackson, A.L. (2013). Metabolic rate and body size are linked with perception of temporal information Animal Behaviour, 86, 685-696 DOI: 10.1016/j.anbehav.2013.06.018