Tuesday, March 27, 2018

Those Aren’t Chocolate, Easter Bunny!

A repost of an original article from March 27, 2013.

The Easter Bunny has a dirty secret. When he’s not hopping around in his pristinely white fur hiding beautifully colored eggs and decorated baskets full of treats…he’s eating his own poo. Gross!

Never trust a rabbit. Photo by the Mosman Library at Wikimedia.

But don’t judge him before you understand him. It’s not that he chooses to eat poop, but that he has to for his own health. In fact, all rabbits do.

Rabbits are herbivores, which means that they only eat plant material. Plant material is very difficult to digest, although it may not seem like it (I mean, we eat plants all the time with no problem, right?). But when it comes to digestion, it’s not what you put in your mouth and swallow that matters, but what your body can break down.

This process of breaking down food depends on digestive enzymes, a group of chemicals that break down food. Each type of digestive enzyme is specific for breaking down a particular type of food chemical. Plant material is so hard to digest because it is largely composed of cellulose, a sugar that we vertebrates don’t have an enzyme for.

Herbivorous animals that lack this enzyme have developed an alternative strategy to get the nutrients they need out of these plants – They have microbes that live in their guts and ferment the plant material. Many of these microbes, which include bacteria, protists, yeast and fungi, produce the enzyme needed to break down cellulose. But these microbes are slow-acting (which means herbivores with longer guts get more nutrients), and they are sensitive (which means herbivores with special microbe gut chambers get more nutrients).

Rabbits have a special gut chamber called a cecum (or caecum) that houses many of their gut microbes. The cecum is so important to rabbit digestion, it’s even bigger than their stomach! When a rabbit eats something, the food is broken down by chewing, swallowed, and passed on to the stomach (follow along with the diagram below). The stomach stores and sterilizes the food while breaking down some of the nutrients before it passes the food on to the small intestine. The small intestine absorbs the nutrients it can before the remaining food gets sorted at a fork in this digestive road. The fibrous food parts move on to the colon, where it is converted into little hard turd-balls. The non-fibrous parts go to the cecum, where the microbes living there work their magic, breaking down the remaining food into absorbable nutrients.

This diagram of the rabbit digestive system was posted by Sunshineconnelly at Wikimedia. Trace through it as we talk about where each digestive step happens.

The trouble is, this food has already passed the part of the digestive tract that absorbs most of these nutrients: the small intestine. Now, it has nowhere to go but out. So the cecum pushes these remaining nutrients into the colon, which turns them into cecotropes (or caecotrophes): mucus-covered, nutrient-rich, moist turds shaped like a bunch of grapes (and according to the Easter Bunny, just as delicious). And the only way rabbits can get the nutrients (and remaining microbes) out of these little nuggets is to send them through the digestive tract all over again by eating them. So that is what they do.

Eating poo sounds gross and unusual, but it is actually fairly common in the animal kingdom. So common, in fact, that there is a term for it: coprophagia. Hamsters and capybaras have similar digestive tracts to rabbits and eat their own poo for the same reasons. Other animals, like elephants, hippos, pandas, and koalas, are born without the necessary microbes to digest the food available, so the babies obtain these microbes by eating their mothers’ poo. And many coprophagous insects, like flies and dung-beetles, subsist on diets composed of the poo of large animals.

So don’t hate on the Easter Bunny for his repulsive ways. He can’t help what he is. Just appreciate him for all the chocolate eggs he brings you every Easter. Wait… Those are chocolate eggs he brought you, right?

Tuesday, March 20, 2018

Physicists Determined That Cats Are a Liquid

Marc-Antoine Fardin, a physicist at Paris Diderot University, was inspired by a post at boredpanda.com called “15 Proofs That Cats Are Liquids” and set out to use the tools of his trade to determine if this is, in fact, true.

Figure from "On the Rheology of Cats": (a) A cat appears as a solid material with a
consistent shape rotating and bouncing, like Silly Putty on short time scales.
(b) At longer time scales, a cat flows and fills an empty wine glass.
(c-d) For older cats, we can also introduce a characteristic time of expansion and
distinguish between liquid (c) and gaseous (d) feline states.

Rheology is the branch of physics that studies the flow of matter. Matter can come in three forms: solid, liquid and gas. Under pressure or stress, solid matter deforms whereas liquid and gas matter flows. Liquid matter is incompressible, whereas gas matter is compressible. Thus, liquids are substances that conform to the shape of their containers (i.e. are fluid) and have constant volume (i.e. are incompressible).

Flow is the process of conforming to the shape of containers and has a set duration for different substances. In rheology, this duration is called the relaxation time. The ability to determine if a substance is a liquid depends then on whether you observe it for longer than its relaxation time. Based on the evidence provided in images, Marc-Antoine determined that cats can, in fact, conform to the shapes of their containers if given enough time. Therefore, cats are liquid.

But this leaves us with additional questions about how cats flow. For one thing, some fluids are more viscous (thicker) at some times and less viscous (runnier) at others. This property is called thixotropy. Do cats exhibit thixotropy? In other words, does the relaxation time of a cat depend on its age? And do they flow with vortices or with laminar flow? A substance flowing with vortices would spin around the container and start to climb of the walls of the container. A substance flowing in a laminar way would calmly follow the outline of their container. Cats may be a fluid that can do both.

Figure from "On the Rheology of Cats": (a) A cat spontaneously rotates in a cylindrical jar.
(b) Normal forces and Weissenberg effect in a young sample of Felis catus.

Clearly, more work needs to be done on this very important question. If you have a cat, you can explore this question with some photographic evidence of your own.

Want to know more? Check this out:

Fardin, M.A. (2014). On the Rheology of Cats. Rheology Bulletin, 83(2):16-17.

Tuesday, March 13, 2018

The Science Life 3

The science life is a stressful one, no matter what stage you're at. Take a music break and know you're not alone.

"Take Exams" by AcapellaScience (parody of "Shake it Off" by Taylor Swift):

"Part of Your Lab" by Florence Schechter (parody of "Part of Your World" from The Little Mermaid):

"Some Budding Yeast I Used to Grow" by Nathaniel Krefman (parody of "Somebody That I Used to Know" by Gotye):

Vote for your favorite in the comments section below. If you would like to see more music videos on the life of a scientist, check out The Science Life and The Science Life 2. 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 post!

Tuesday, March 6, 2018

Caught in My Web: Marine Technology

Image by Luc Viatour at Wikimedia Commons
For this edition of Caught in My Web, allow yourself to be amazed both by the range and depth of behaviors of marine animals, and by the incredible technologies we have used to learn these things.

1. Penguincams show that Gentoo penguins “talk” to one another while foraging and you can see some of the penguincam footage here.

2. Scientists built an 8-foot touchscreen for the dolphins at the National Aquarum in Baltimore and discovered they like to play “Whack-an-Angelfish”.

3. Using audio-recording tags, we learned that mother and baby humback whales “whisper” to one another to avoid predators.

4. Scientists created virtual reality holodeck for zebrafish.

5. Thanks to the fact that zebrafish larvae are transparent, scientists have discovered a way to image brain activity in an animal as it is behaving in real time. Humans may be cool enough to have developed this technology, but now we know that zebrafish have developed predator eversion strategies when they are still larvae.

What will we come up with next?