Tuesday, December 12, 2017

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.

Tuesday, December 5, 2017

Why Reptiles Won't Wear Fur

A reposting of an article from September 19, 2012.

Have you ever seen a furry lizard? A fuzzy snake? A wooly turtle? Me neither. That's because a reptile in a permanent fur coat would whither like Superman with a pocket full of kryptonite. But why? Other animals are so content in their soft, luxurious layers... Why can't reptiles be?

"I wouldn't be caught dead in that fur coat you're wearing". Photo by Naypong at freedigitalphotos.net.
Animals exchange heat with their environments in four major ways: conduction, convection, radiation and evaporation:

  • Conduction is when heat moves from a hotter area to a colder area across a still surface. If you stand barefoot on a cold sidewalk, the heat in your feet is going to transfer to the cooler surface of the sidewalk by conduction and you will get cooler (which is nice in the hot summer, but uncomfortable when the weather starts to get chilly). Conduction can happen when the body is in contact with a solid (like a sidewalk), a liquid (like a bath), or a gas (like the air around you).
  • Convection is essentially conduction with movement, and this movement makes the transfer of heat even faster. If you are standing inside and it is 70ºF in the building, you will likely be fairly comfortable. But if you are outside on a windy 70º day, even though the environment is the same temperature, you will get colder faster.
  • We are all familiar with the warming effects of the sun's radiation, but in reality, all objects give off electromagnetic radiation. Radiation within the visible spectrum we perceive as colored light, but most radiation is outside our visible range.
  • Evaporation happens when water (like sweat or moist breath) converts from a liquid state to a gaseous state, taking heat away from the body. Animals are always in contact with something (like surfaces, air, or water), so conduction is always occurring.
The speed at which an animal's body heats or cools depends on the temperature difference between the animal's body and its environment. That is, in a very cold environment, an animal will cool quickly and in a very hot environment, an animal will heat up quickly, whereas in an environment that is close to the animal's body temperature, the animal will heat or cool very slowly. To put this in mathematical terms, let's call the animal's body temperature Tb and the environmental temperature Te. The bigger (Tb-Te), the faster the animal will cool. And the bigger (Te-Tb), the faster the animal will heat up. This difference between Tb and Te (in either direction) is called the driving force of heat exchange.

Imagine this circle is an animal's body, Tb is the animal's body temperature and
Te is the environmental temperature. The bigger (Tb-Te), the faster the
animal will lose heat and cool down.

This works the other way around, too.
The bigger (Te-Tb), the faster the animal will heat up.

What happens if you put fur on that animal? Now you can imagine this animal as having two separate layers, a body (with the temperature Tb) and an insulation layer (with the temperature Ti). Now for heat to be exchanged, it has to be conducted twice, once between the environment and the insulation, and again between the insulation and the animal's body. Ti is always going to be some intermediate temperature between Tb and Te and so the driving force of heat exchange will be much lower and the animal will heat up or cool down much more slowly. The thicker this insulation layer, the more stable Ti becomes and heat exchange happens even more slowly. Also, because insulation prevents movement at the body's surface, insulation layers eliminate any heat exchange at the body's surface (but not the surface of the insulation layer) by convection. (By the way, this logic also holds true if the animal has feathers or blubber or even a winter coat).

This inside circle represents an animal's body and the outside circle shows its insulation
layer. Tb is the animal's body temperature, Te is the environmental temperature and Ti is
the insulation temperature. Ti is always between Tb and Te, so the driving force of
heat exchange is reduced and the animal's body temperature does not change quickly
at all, even if the environmental temperature is extreme.

Most animals that have fur are mammals, as are most animals with blubber layers (like seals and whales) and animals that wear coats (like people and Paris Hilton purse dogs) and most animals with feathers are birds. What do these insulated mammals and birds have in common? They are endotherms. They generate most of their own body heat. This means that by slowing the exchange of heat between the animal's body and environment, the animal is provided with more time to generate heat and the insulation then helps to preserve this heat.

But reptiles (as well as amphibians and fish) are ectotherms. They get almost all of their heat from their environments. They maintain their body temperatures behaviorally, by choosing what environment to hang out in and what position to put their body in. If they are cold, they go bask in the sun to absorb radiation heat or lay on a warmed rock to absorb conducted heat. If they are hot, they lay on a cool rock in the shade to lose heat by conduction or soak in a cool stream to lose heat by convection. To maintain a relatively constant body temperature, they are constantly moving between warm and cool areas to adjust their body temperature one direction or another.

Many ectotherms rely on their ability to adjust their body temperatures quickly, and this ability depends on creating large driving forces of heat exchange. If an ectothermic reptile were to have an insulation layer, like fur, it would reduce its ability to adjust its body temperature by conduction and convection. It would lose its heat slowly and not be able to replace it fast enough. In the end, it would become too cold. It may seem paradoxical, but a lizard in a fur coat would likely die of cold-related physical issues (if not embarrassment).

Interestingly enough, just because lizards don't have fur doesn't mean they couldn't have hair. In fact, some of them do have hair, but not how you may think. Hair, fur, feathers, and scales are all made up in large part by keratin proteins. Many gecko species are well known for their wide, sticky toes that help them climb smooth, vertical surfaces (like walls). Their secret? Ultra-thin keratin hairs growing out of the geckos' feet provide a chemical adhesive force to keep the animal secured to the wall surface. So reptiles may not have a need for fur, but some of them have an innovative use for hair.

Want to know more about hairy geckos?

Autumn K, Liang YA, Hsieh ST, Zesch W, Chan WP, Kenny TW, Fearing R, & Full RJ (2000). Adhesive force of a single gecko foot-hair. Nature, 405 (6787), 681-5 PMID: 10864324

Wednesday, November 22, 2017

Eye Didn’t See That

By Evan Hovey

A grandmother and her grandson watching the television.
The elder is straining to see while the young man is not having any troubles.
Photo by Evan Hovey.

It’s Thanksgiving and the family just finished stuffing their faces full of turkey and cranberry fluff. Everyone meanders into the living room to sit down, let the tryptophan sink in, and watch some football. As you sit there, you start to observe the older family members around you take out their glasses or bifocals and squint towards the television in attempts to see what is going on. You begin to ponder the thought, “am I going to start to lose my eye sight as well?” Well, as it turns out, as you age, the number of cells that respond to light and color (called photoreceptors) begins to decrease.

Songhomitra Panda-Jonas, Jost Jonas, and Martha Jakobczyk-Zmija at the University of Erlangen-Nurnberg, Germany, looked into the number of photoreceptors in the retina of the eye to determine whether there was a loss as you age. The retina is the thin layer of tissue that lines the back of the eye. It is the location where your eye transfers what you see to the brain. There are two different kinds of photoreceptors in your eyes: rods and cones. Rods are those that detect light at low levels, which is what helps us see at night. Cones, on the contrary, are those that take in high light levels and help decode color. The authors believed that there would be a decrease in both kinds of photoreceptors as the eye got older (the older the person, the fewer photoreceptors). They came up with this hypothesis in part because of prior knowledge of a loss of tissue associated with vision in other parts of the eye as you age.

The researchers approached this study by obtaining fifty-five eyes from human donors that died at ages ranging from 18-85. The eyes were removed from the bodies less than eleven hours after death. Then the eyes were cut open and tissue samples from the retina were obtained. To determine the amount of photoreceptors in the tissue samples, the researchers used an ultrasound to view the retina and counted the photoreceptors on a photograph taken with the ultrasound. The two different kinds of cells were distinguished by their sizes (the larger cells were the cones and the smaller cells were the rods).

The results they found were as expected: the older you get, the fewer photoreceptors you have and the worse your eyesight is. The decline of the number of photoreceptors was at a constant rate throughout all ages of life. However, the number of rods declined faster than the number of cones. The loss of these photoreceptors causes you to view things with more difficulty. As your rods die, you begin to develop night blindness (the inability to see well in poor lighting or darkness). When your cones die, you begin to lose more of your visual perception, which includes straining when looking at something from a distance, as well as affecting how you see fine detail such as reading a book or looking at a television. The combined loss of your rods and cones is part of what causes older individuals to have more vision problems.

As you progress through life, your photoreceptors decline, causing your vision to get worse. As you sit down after Thanksgiving to enjoy some good old-fashioned fall football and the elderly people strain to see the television, you now know that the oldest person in your family is most likely having the hardest time seeing that big touchdown.

If you would like to read the actual paper, the source is located below:

Panda-Jonas, S., Jonas J., Jakobczyk-Zmija, M. (1995). Retinal photoreceptor density decreases with age: Ophthalmology, 102 (12), 1853-1859

Tuesday, November 14, 2017

Let’s Talk Turkey: 8 Surprising Facts About Turkeys

A reposting of an article from November 24, 2014.

A wild male turkey struts his stuff.
Photo by Lupin at Wikimedia Commons.
1. Turkeys are all-American. The modern domesticated turkey is descended from the wild turkey of North America, which is essentially a pheasant.

2. Domestic turkeys can’t fly or have sex. Domestic turkeys have been bred to have enormous breast muscles for our dinner tables. Their breast muscles have become so large that these top-heavy birds have lost the ability to fly and even to have sex! Domestic turkey eggs now have to be fertilized by artificial insemination. Wild turkeys with their functionally-sized breast muscles, however, can fly up to 55 mph for short distances and have sex just fine.

3. Male turkeys (called toms) are courtship-machines. Wild turkey males are substantially larger than females, and their 5,000 to 6,000 feathers have red, purple, green, copper, bronze, and gold iridescence. Like peacocks, male turkeys puff up their bodies and spread their elaborate feathers to attract mates and intimidate rivals. In comparison, female wild turkey feathers are duller shades of brown and grey to better hide from predators. And as if their flashy feathers weren’t enough, toms also have fleshy body appendages called snoods (the fleshy snotsicle that hangs over their beak) and wattles (the thing that looks like a scrotum under their chin). When the male is excited, the snood and wattle fill with blood and turn bright red. Sexy!

4. Turkeys are intelligent animals. They even have the ability to learn the precise details of a 1,000-acre area. And no, turkeys will not drown if they look up into the sky during a rainstorm.

5. Turkeys are social animals. They create lasting social bonds with each other and are very affectionate. Turkeys can produce over 20 different vocalizations, including the distinctive gobble (produced only by males), which can be heard up to a mile away! Individual turkeys have unique voices that they use to recognize each other.

6. Female turkeys (called hens) are good moms. Wild turkey babies (called poults) are precocial, which means that they hatch out of their eggs already covered in fluffy down and able to walk, run and feed themselves. They stick close to their mother for protection from predators, but unlike many other species of bird mothers, she doesn't have to feed them. Although wild turkeys roost in the trees at night to avoid predators, poults are unable to fly for their first few weeks of life. The mother stays with them at ground level to keep them safe and warm until they are strong enough to all roost in the trees with her.

A wild turkey mom and her poults. Photo by Kevin Cole at Wikimedia Commons.

7. Ben Franklin wanted the turkey to be America’s national bird. Benjamin Franklin famously argued that the wild turkey, not the bald eagle, should be America's national bird. In a letter to his daughter, he wrote, "For my own part, I wish the bald eagle had not been chosen as the representative of our country; he is a bird of bad moral character; he does not get his living honestly...like those among men who live by sharping and robbing...he is generally poor, and often very lousy. Besides, he is a rank coward; the little king-bird, not bigger than a sparrow, attacks him boldly and drives him out of the district...For in truth, the turkey is in comparison a much more respectable bird, and withal a true original native of America. Eagles have been found in all countries, but the turkey was peculiar to ours...".

8. Turkeys were once endangered. Although millions of wild turkeys used to live across the Americas, they were almost completely wiped out due to a combination of over-hunting and habitat destruction. Thanks to strong conservation efforts that included better hunting management, habitat protection, captive breeding, and reintroduction into the wild, wild turkey populations are now healthy and found in all of the lower 48 states.

Tuesday, November 7, 2017

Science Beat: Round 8

It is midterm time again. If you learn science better with a beat, check these out:


Cellular Biology:

Anatomy and Physiology:

Vote for your favorite in the comments section below and check out other science songs worth learning at Science Beat, Science Beat: Round 2, Science Beat: Round 3, Science Beat: Round 4, Science Beat: Round 5, Science Beat: Round 6, Science Beat: Round 7, and Science Song Playlist. Check out some song battles about the life of scientists at The Science Life, Scientist Swagger and Battle of The Grad Programs! And if you feel so inspired, make a video of your own, upload it on YouTube and send me a link to include in a future battle!