eyes on the horizon

Horizontal pupil of a goat (flickr.com)

 Literature and lore often depict satanic or demonic animals as having hooves, horns, and elongate pupils. But my experience with goats, their delicious cheese and cute little tongues lapping up food at a petting zoo suggest otherwise. So I’m going to go ahead and make a bold statement: maybe these attributes are not markers of a demonic origin, but adaptations for predator avoidance and feeding.

You’ve probably noticed that livestock animals like horses and cows have horizontally rectangular pupils? Admittedly, this difference from our own eyes can make them seem unrelatable and a little spooky… probably interpreted as “demonic” by scribes of old. But look at the eyes of an animal, you can make inferences about where they spend most of their time, and what sort of predation they are likely to face.

Wide-angle view of ungulates, thanks to eyes being on
either side of the head and horizontally stretched pupils.

Ungulates (hoofed animals like deer, goats and sheep, bovine, horses, etc. that graze on grasses) all have the horizontal pupils, and eyes generally situated on either side of the head. This adaptation gives them an expanded range of peripheral vision. As grazers that must keep their heads down in open fields and grass plains, they have to be able to keep an eye on the horizon for Mufasa and Simba coming to eat their asses, even as they are munching on grass. Once motion is spotted, the zebra/sheep/antelope/whatever is equipped with long legs and speed that usually gets them out of hot water.

Reduced angle view that carnivores
experience.

The predators of these ungulates have vision adaptations of their own. Their eyes are situated more on the front of their head, causing the images seen by each eye to overlap. This is called binocular vision, and allows the animal keen depth perception fitting for a hunter. Of course, they trade wide-angle peripheral vision for their depth perception. But as predators and not prey, they don’t need to monitor the expansive horizons for danger as attentively. In addition, rounded pupils allow for super-tight focusing, perfect for spotting a tasty morsel off in the distance. Great depth perception + focusing power = zebra for dinner.

Can you think of any other animals with crazy eyes? Or eyes placed on the head differently than they are on yours? What do these things tell you about the animal's role in the food web?

try to b positive

Do you know your blood type? I do. Turns out, I’m a proud B positive. Representin’ homies.

A few years ago, I had my blood typed out of curiosity. They had to take three vials of blood to complete the test- which I initially found absurd. But when I stopped to think about how the blood typing system works, three vials made sense.

You’ve heard the blood types before: A, B, O, or AB with a positive or negative stuck on the end. What these letters really represent are proteins that belong to the ABO blood group. You see, on the surface of all your red blood cells are imbedded little proteins in the membrane. These are fittingly called- wait for it- surface proteins. They act like identity badges, marking the cell according to which protein floats in the cell membrane. Maybe you have A proteins, or B proteins, or both, or neither. If you have both, you are an “AB” blood type. If you have neither, you are an “O” blood type (O really stands for “none”). So, if you’re “A,” you are technically either “AA” or  “AO.” At the end of the day, you only have “A” proteins so you are just called an “A” bloodtype. Same thing goes for us B types.

There’s another category of surface proteins, known as the Rhesus blood group, or “rh” for short. If you have rhesus proteins, you are “rh-positive.” If you don’t, you are “rh-negative.” This is where the positive/negative part of your blood type comes from.

When blood transfusions take place, phlebotomists must make sure to not give blood with any proteins that the recipient does not originally have. For instance, if you were to give A positive blood to a B negative person, their body would be all “what are these B proteins?! And rh proteins?! Ah HELL no!” and attack those cells. Give that very same person A negative blood, and there’s no problem. Their body would not detect any proteins with which it was not already familiar.

With this knowledge, you can figure out that O negative blood would be accepted by anybody, since it has no proteins for a donor to reject. This is why O negative people are called “universal donors.” Conversely, AB+ blood may only be accepted by AB+ people, since it has all possible surface proteins that could cause a immune reaction. Likewise, AB+ people can accept any blood, since their bodies are already familiar with all three of the possible surface proteins. Ah lah, AB+ people are called “universal recipients.”

All of these proteins are inherited genetically. Each parent can contribute one protein of each category. An “AB” parent can contribute either their A or their B, while an O parent has nothing to offer. So, if Judy (O negative) and Bill (O negative) have a B positive child, Judy got some ‘splainin to do. Blood types were historically used as paternity tests, but as you can see, can sometimes be inconclusive. They are only able to rule out, not determine, a parent- and only part of the time at that.

Armed with the knowledge that there are three possible proteins that may determine a blood type, I understood why that vampire nurse bled me like a stuck pig when I went to get my blood typed. They needed one vial to test for A proteins, one to test for B proteins, and one to test for the rhesus group.

Do you know your blood type? Go find out. Then, I dare you to figure out all the possible blood types your parents could be. It’ll be so much fun!

making heads or tails of phospholipids

Cells are, in some ways, measurable units of life. Life started out as single, functioning, living, cells. In school, they teach you to associate cells with fancy words like “endoplasmic reticulum,” “organelle,” and “Golgi apparatus.” Look past those biology tests from high school, and you can appreciate what a cell is on a deeper level. It is a division from the environment. Outside of the cell is non-living space, and inside of the cell is life. The structures that are ticking within the cell must be housed, separate from the watery dead-space around them. That housing must also provide a means of transport for waste and nutrients to leave and enter the cell, as we know a living system is not a closed system. How does the membrane of a cell work?

Figure 1: A single phospholipid

The membrane of a cell is made up of a phospholipid bilayer. When you break those terms down, you can see it has something to do with phosphorous, lipids, and two layers. Phospholipids are two-part molecules- on one end, a phosphate group- called the head; on the other, two dangly chains of fatty acids- the tail (Fig. 1).

The phosphate head is polar, while the fat chains are non-polar. Polar simply means that the charges within the molecules are more clumped than evenly distributed. Polar molecules are attracted to other polar molecules, like, oh say, water. As a result, the phosphate heads love to snuggle up next to water, and always try to acclimate so that they are in contact with it. As for those fat chains, well, they’re lipids. And we all know that lipids (oils, fats, wax) repel water. Slap some fancy terminology in there, and we have a molecule with one hydrophilic (water-loving) end and one hydrophobic (water-fearing) end.

Figure 2: Phospholipid bilayer that forms a cell membrane

The end result of all this is that phospholipids tend to form sheets, where the hydrophobic fatty acids are sandwiched in between the protective phosphate heads, which are exposed to the aqueous environments inside and outside of the cell. These sheets form the shell of a sphere, and are the cell membrane (Fig. 2).

Now, let’s apply this setup to reality. The phospholipids are not cemented in place, and in fact shuffle amongst each other like tightly-packed floating ducks in a bath tub. This non-static membrane system is described by the fluid mosaic model.  That basically says that cell membranes are fluid (non-static) and mosaic in nature (made up of sub-units). Ah lah, a membrane that is made up of subunits that float and shift to form an ever-changing cell surface. 

I like this cell membrane business because it shows how a bunch of non-living molecules like phosphates and fatty acids can work together to form a system that is living. Because of the fluid mosaic model and it’s important duty of dividing non-life from life, the spectrum of “living” spans from an itty bitty amoeba to a T-rex. As complex as we are as vertebrate organisms, it’s important to remember that we are complexities made up of even more complexities. Complexities like phospholipids, that are flashes of our humble beginnings as single cells- a collection of working parts, housed together.

big gurl hongry

Here in Alaska, the temperatures have dropped a good bit recently. We went from having highs in the 60’s to highs in the 20’s. Considering I’ve only ever lived in Texas, Louisiana, and Alabama and used to shiver at 60°, I’d say I’ve adapted very well. I have noticed an unexpected side effect however: increased grocery bill. I mean, like double. But what’s an endotherm to do?

I’m sure you’ve heard the terms “warm-blooded” and “cold-blooded.” Those are silly. Let’s use “endotherm” and “ectotherm.”  They describe an animal’s strategy to temperature regulation. You see, all animals have an optimal temperature at which their metabolic processes occur most efficiently. So life has developed ectothermy and endothermy as ways to maximize the bang for your buck. Or, energy for your food, as it were.

And herein lies a common misconception. Heat is not the end-goal of metabolism; you do not eat food for the purpose of heating your body. You- and all animals- eat food to power your systems, like the muscle fibers that contract to make your heart beat, or the network of brain cells that allow you to form thoughts. True, heat determines the efficiency of these functions, but does not directly power them.

As an endotherm, your body produces heat from the inside. Humans have evolved to produce- and dissipate- enough calories of heat to keep our bodies at a steady 98.6°. Each and every one of your living cells contributes a bit of by-product heat in the midst of its own chemical reactions to maintain this temperature.

Ectothermic animals absorb heat from their environment- not as a means of energy acquisition- but simply as a means of heat acquisition. They also dissipate heat to the environment- think of a snake hiding under leaves trying to escape the hot sun. Here, it is easier to see that heat ≠ energy when it comes to metabolism. It’s all about keeping the body at its optimum temperature- and for ectotherms, that temperature is usually significantly lower than that of endotherms- hence the warm/cold blooded silliness (but, the temperature of the blood of the animal doesn't determine nor describe how it temperature regulates- ectothermic and endothermic do. They win).

To me, the really interesting difference between endothermy and ectothermy is how they keep temperatures regulated: endothermy by physiology, ectothermy by behavior. Endotherms’ (mammals and birds) steady metabolic reactions take care of the temperature regulation for them. Ectotherms (reptiles, amphibians, fish, etc.) must actively scuttle between shade and sunny spots to either absorb heat or dissipate it, always trying for that sweet spot.

Hot breath from a dinosaur? Could it be?

You know that scene in Jurassic Park where the brother and sister are hiding in the kitchen and the velociraptor peers in through the kitchen window and fogs it up with its hot breath? Well, seeing as we know reptiles are ectotherms- what do you think of that? Have we caught good ole Spielberg in a blunder?

Of course we haven’t; he’s Steven Spielberg. Once an exothermic species reaches a certain size, heat from metabolism is actually unable to escape from the large body. The density and size of the body keeps internal heat from dissipating to the environment, in effect, making the animal endothermic. This is called gigantothermy- and all large dinosaurs are thought to have been gigantotherms. So indeed, a velociraptor would probably fog the window up with its breath before it ate your ass.

Now, I must go consume the family-sized portion of red beans and rice I made for supper. It’s frickin cold here, folks. Girl’s gotta supply her chemical pathways with carbohydrates and protein so they can release heat to keep her little body warm. Don’t judge.

a delicious anomoly

Somebody's lame (but oh-so-comfy) shoes and socks

What is your reproductive strategy? Are you the jerk with the popped collar who hits on every girl ever, knowing that with an increased sample size comes increased odds of taking one home? Maybe you’re the sassy lady who dresses to the nines to increase visibility of your secondary sexual characteristics (sexual traits other than the obvious one- like boobs). Maybe you have good intentions to be attractive but find yourself wearing “active casual shoes” with striped socks and high-water jeans to work and wonder what happened to your self respect.

Well, let me just go ahead and answer the question for you. You, PUNY HUMAN, have an iteroparous reproductive strategy.

Iteroparity and semelparity are the two main approaches life can take to reproduction. Semelparous organisms are usually short-lived and “put all their eggs in one basket,” if you will. They pool all their bodily resources into a single reproductive event and then die. Think about those clouds of gnats that buzz around in your yard during the summer. Those little gnats are just a few days old and are already having a giant orgy. After their thousands of eggs are fertilized and laid, the bugs’ tiny bodies are so exhausted and depleted that they die. Then just days later, their offspring emerge and the cycle starts again. This is semelparity.

Iteroparity (latin for “to beget repetitively”) is characterized by multiple reproductive events before death- ones that usually occur over a much longer time span. Almost all vertebrates are iterparous and invest only part of their physical resources towards gravidity, allowing them to live past each reproductive event and have future ones. Subsequently, iteroparous organisms have longer lifespans and experience more growth.

Of course, each strategy has its pros and cons. Semelparous events are usually so large that a single gnat will have more offspring in a single event than you, as an iterparious critter, ever will. Iterparous organisms generally live longer, experience more parental care, and grow larger; therefore they have increased fitness and odds of surviving the elements (gnat vs. human in high winds or something of the like).

I’ve been living in Alaska for a few months now and have become well acquainted with one of the foremost exceptions to the semelparity/iteroparity trends. The Pacific Salmon is a relatively large vertebrate with a fascinating reproductive cycle. First off, a little salmonlet hatches in a freshwater stream. The newborns hang around in their stream anywhere from a few months to a few years, depending on the species. During this time, 90% of them will die. When they have grown into little silver fishies, they swim down the streams and into the salty ocean, where they will spend up to five years swimming around and eating. During this time, they grow in size and sequester the nutrients that the ocean has to offer. After five or so years, it is time to do the hanky panky.

These incredible fish find their way back to the same spot on the shore from which they emerged as little tiny salmon years ago, with their destination being the original stream in which they were hatched. There, females lay eggs and males fertilize them and are responsible for defending the nests. Their bodies, ravaged from the long journey from the ocean and reproduction are physiologically spent. At this point, the fish begin to die.

When this sexy journey begins, the physiology of the fish changes into reproductive mode. This means they completely quit eating, and their bodies begin to consume reserves and tissue for energy. Some species undergo a color change- males becoming bright red to attract the lay-des, and their mouths changing so dramatically as to become hooked with a ferocious set of teeth. Aside from their bodies being energetically depleted, this new morphology is completely unsuitable for life in back the ocean. Any way you slice it, it is the end of the road for these fish.

Top: Sockeye salmon before reproductive journey
Bottom: Sockeye salmon during reproductive jounrey
(adfg.alaska.gov)

And there you have it- a single reproductive event before death. Semelparity. But in a vertebrate that devotes five years and hundreds of miles to becoming a 4 pound hunk of impressive fish! It is an anomaly. But it is a successful enough strategy to cause the yearly Pacific Salmon runs to be stable, repetitive, and critical cornerstones of coastal ecosystems of the great Northwest.

It seems as though the odds are stacked against these guys. They must overcome so many treacherous obstacles- not being eaten as an egg and surviving larval-hood, dodging the hungry predators of their natal streams, enduring 5 years in the perilous ocean, and then making the arduous journey back (without being caught by a bear or fly fisherman). But nonetheless, it works. Millions of years of natural selection and random chance have whittled what we see as statistically unlikely into a highly refined, highly adapted system.

AND, they taste really good. Especially when fresh. And with butter.

nature's russian nesting dolls

Geoff Grammer, evolutionary baggage reader and master of science geekery, requested I write a little something up about reoccurring patterns in nature, and more specifically, fractals. But the two topics are so interesting that I think we should cover just one per post. Fractals, you’re up.

Fractals are physical phenomena where patterns occur infinitesimally within themselves. You could say they are the Russian nesting dolls of natural design. The same design occurs over and over within itself; the catch being that it does not lose detail with magnification level. For example, the crystalline structures of snow flakesare just the same when looking at the flake with your naked eye as it is when you put it under a microscope. Ice crystals, lightening bolts, sea shells, fiddleheads, animal coloration patterns, blood vessels, and various vegetables are a few well-known instances of fractal development. You could generalize and say that things that “branch” have a tendency to exhibit fractals. Let’s begin our tour-de-fractals.

Lichtenberg figures are the nifty designs that electricity produces when traveling through an insulator. They show the branching paths that electricity wants to take when it travels. Often times, lightening-strike survivors have Lichtenberg figure burns on their skin. They represent electricity's tendency towards entropy- little fingers desperately stretching in all directions seeking a medium by which to travel.

Man struck by lightening marked by Lichtenberg figure
(en.wikipedia.org)

A full head of Romanesco broccoli
(fourilab.ch)

Romanesco broccoli is what we call an approximate fractal, since the pattern does not exactly occur infinitesimally- but pretty darn close. Once it reaches a very tiny size, the pattern ceases. But for some magnification levels, each little bud looks like an entire head of broccoli. And each bud on that bud looks like an entire head of broccoli. And each bud on that bud on that bud... okay I'll stop. Same deal with the fronds of a fern.

Ice crystals are fractal in nature. They are always hexagonal and symmetrical- but no two are exactly the same. When a snow flake lands on you, you can see with your naked eye that it is snow-flakey looking (hexagonal and symmetrical). Take it apart, and you will see that it is really a clump of ice crystals, each of which is snow-flakey. As the frozen water masses fall through different temperatures and humidity, ice crystals form on the ice crystals. It is this stage of formation that creates the details that make each snowflake unique. In the pictures below, you can see the "pieces" of a snowflake and how they come together to make more intricate, larger versions of themselves.

(wikipedia.com)

When people see the detail and "perfectness" of such things, they often say "how could that just happen? There's got to be something bigger." And I agree- there is something bigger. It's the definition of "something bigger" that varies from person to person. But really, does that definition matter that much? I think we can all agree on the impressiveness of nature when viewed through a microscope.

you're so vein

Arteries and veins are the major vessels that carry blood to your body parts. Arteries carry blood away from the heart, while veins carry blood back to your heart. Although these vessels seem to be identical mirror images of each other, they are certainly not. There are profound differences between arteries and veins.

Arteries are more highly pressurized the veins, since they are at the beginning of the circuit and carry blood being pumped right out of the heart. Like a garden hose with one of the spray triggers on the end: the water pressure is greatest right at the opening of the trigger, and less the farther away from the opening you get. To account for this pressure, the walls of the arteries have a layer of muscle that contract in rhythm with your heart to absorb the pressure waves (so when you feel your pulse in your wrist, it is this muscular contraction you are feeling rather than the pressure wave from your heart).

Veins are not muscularized and so do not assist in pumping blood back to the heart. On top of not having any muscular getty-up, the blood they carry is under little pressure on its way back to the heart. And furthermore, blood has to fight gravity on its way back to the heart, seeing as most of the body is below the position of the heart. So what makes blood "go" in the veins?

Skeletal muscle contraction squeezes it back through the veins. Walking, running, playing hackysack (that’s what the kids are doing these days, right?), any motor activity squeezes the blood like toothpaste through your veins. But there is still the low pressure issue, so there must be a mechanism in place to keep backflow from occurring- especially in the legs, where gravity is pulling it back down towards the feet. Once again, nature has got it covered.

Left: valve open, blood moves forward
Right: valve closed, blood is stationary

Your veins have little one-way valves in them that open when blood is squeezed forward, and shut when pressure drops and gravity starts to pull it back down. These valves are passive, meaning they require no expenditure of energy and no innervation. They run off of gravity and blood pressure generated by skeletal muscle contraction. An elegant solution. Unless, these valves fail. 

If the valves become worn out and do not close completely, backflow of blood occurs. This pooling of blood generates little out-pockets along the veins. Fairly benign, but unsightly. We call these "varicose veins." 

Two questions for you:

1. When you sleep and are not moving, how is blood squeezed back through your veins? Hint: Latin word for "partition"

2. Say you were in a severe car accident. The powers that be give you the option of having either an artery or a vein severed. Which would you choose and why?

stop it, your bib is turning me on

Male house sparrow (gardening-for-wildlife.com)

We all have those certain “turn-ons” that get us going. For me, a solid set of shoulders and manly forearms catch my eye. And a little stubble never hurt anyone. And dark hair. Oh, and strong hands.  And a defined jaw. But I digress. Unlike human males, male house sparrows have black patches on their chin and upper chest, known as badges. It looks like they’re wearing little bibs. Some males have large ones, some have smaller ones (he he). Now, when one sex has a characteristic that the other doesn’t, one must always question if it plays a role in sexual attraction.

My taste for square shoulders and strong forearms is clearly linked to fitness. The latent cavewoman in me sees a potential mate who can build shelter and fight off threatening people or animals. Therefore, it is in my and my future offsprings’ best interest for me to be attracted to a male who is physically strong. But how is a black bib linked to fitness? Does it function in camouflage? Make the bird healthier in some way? What’s the deal?

A study by behavioral zoologist Anders Moller took a closer look at house sparrow badges. Come to find out, males with larger badges occupied prime real estate with more nesting sites. Territory defended by males with big badges had safer nests and fewer hatchling fatalities. So this showed that the bigger the badge, the more successful the offspring. But on top of that, Moller found that the big-badged males were… well, pimps. He pumped some females full of estradiol to get their lebidos up, and they were all over those big-badged males like a cheap suit. Poor little small-badged males were just sitting there, dejected and alone. Like me at my eighth grade dance.

So, back to the question. How does a badge function in fitness? Moller’s study reveals that the badge is a signal of fitness, but not a direct determinant. Which is really neat, I think. These types of characteristics- ones that signal but don’t directly function in fitness- show the nuances of evolution that go deeper than “survival of the fittest.” That black bib didn’t make ancient sparrows more likely to survive. Somewhere along the line, by chance, ancestral sparrow males with bigger badges happened to have more fit offspring frequently enough to make it significant. Then genetic drift began to waltz with selective pressure and chance, and before you know it, having a big black throat patch makes you an irresistible house sparrow.

Human sexual attraction seems to be so much more complicated than house sparrows. Do we have fitness signals? If so, what might they be? How do they compare to badges of the house sparrow?

Here's the Moller paper. Ya' know, for fun.

Badge size in the house sparrow Passer domesticus

BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY

Volume 22, Number 5 (1988), 373-378

i'm feeling a little gassy

Fancy me this.

Let’s say you were to fill a Ziploc baggie partly with air and a little bit of solid mass. What would happen if you put it in a tank of water? Depending on the air:solid ratio, it would settle at one particular depth and stay there. Try to force it down, it will float back up. Pull it up, it will sink back down. To make it rest at a different depth, you have to alter the air:solid ratio. But in a closed system like a Ziploc- or a fish- how can buoyancy be adjusted to change depth?

In most fish, there exist buoyancy-control organs called the swim bladder. In some fish, the swim bladder is connected to the digestive tract and the fish can gulp air at the surface to expand the bladder, expel it to contract the bladder. So in that case, the fish is not exactly a “closed system”. The more air the fish gulps, the higher it settles in the water column. If it wants to descend, it burps some out.

In other fish, the swim bladder is unconnected to any other system. No amount of burping or gulping air will affect the fish’s buoyancy. Instead, a gland moderates how much gas fills the swim bladder. Fittingly, it is called the gas gland and excretes both lactic acid and carbon dioxide. The resulting reactions cause hemoglobin to release its oxygen from the blood stream, which then inflates the swim bladder. Up the fishy goes.

Oxygen diffuses back into the bloodstream and goes home to its hemoglobin at another little structure called the oval window. Down the fishy goes. And then the cycle is free to start again.

Although the sea kind of freaks me out, I do think it’s pretty neat that its residents must locomote in one more dimension than us. Our physiology does not need to accommodate “floatability.” Otherwise, we would have to evolve some sort of regulator like a swim bladder.

five fabulous phyla

In “an ant rant,” I asked readers how you could tell a boy ant from a girl ant. One person responded (I’m crying inside, btw), and he answered correctly.  In a haplodiploid reproductive system, the sex-determining factor is the number of chromosome sets an individual has. Females have two sets of chromosomes and are therefore diploid. Males have only one, and so are therefore haploid. So, Roger Birkhead, this one goes out to you.

Today, we’re going to do a quick tour of five phyla of animals that receive way too little attention. Most of them are microscopic critters that are unloved either because A. go unnoticed B. lack a bilateral body plan. Let’s push through these prejudices.

a typical Rotiferan (ucmp.berkeley.org)

Rotifera: means “wheel bearer” in latin.  Usually only a fraction of a millimeter, you need a microscope or a dissecting scope to get a good look at them. They live in freshwater and can either be sessile or travel by inching along a substrate. These guys look like they are wearing little crowns, called coronas, which are rings of cilia around the top of the head that help to filter food into the mouth. The coronas can be quite elaborate. They are capable of sensing light with their little eyespots, though incapable of forming images. They play an important part in freshwater ecosystems and are part of the beds of lakes and rivers.

Velvet worm (brittanica.net)

Onychophora: meaning “claw bearer” in latin. More commonly known as velvet worms. These soft-bodied curiosities live in tropical areas and look a lot like caterpillars, coming in a variety of eye-catching colors. They have tiny eyes and antenna, squirt slime at their prey to catch it, and give live birth. Their stubby feet are particularly interesting structures. There can be up to 40 jointless, hollow lobopods (lobed appendages) that terminate in two hardened claws that help the animal to travel treacherous surfaces. Weirdly enough, they are becoming popular in the pet trade.

Jaw worm (zmuc.dk)

Gnathostomulida: meaning “jaw mouth." More commonly known as jaw worms. They glide along the submerged sand grains in coastal areas. They are a little less than a millimeter long and are pretty much little threads with jaws at the end. They are extremely basic little animals. In fact, their most complex parts are their mouths, which resemble those of rotifers and therefore suggest that they are related phyla. Their digestive system ends in a “blind terminus”- meaning, they have no butt. Food simply enters and absorbs.

A sea cucumber (wikicommons)

Echinodermata: meaning “spiny skin.” This phylum includes sea stars, sand dollars, sea cucumbers, and sea urchins. Most follow a pentaradial body plan, meaning that they are arranged around 72° segments. Although sea cucumbers are heavily derived, they do follow a pentaradial body plan that is more easily seen in early stages of development when they are just little cucumberlets.

Rhombozoan
(simple.wikipedia.org)

Rhombozoa: Known as “lozenge animals.” These are parasites that live inside of cephalopods (squid, octopi, cuttlefish, and nautiluses). They may grow to be several millimeters long and are surrounded by ciliated cells. So, they look like tentacle-covered threads that attach to the kidney cells of cephalopods, from which they receive all nourishment. Very strange.

That completes the tour of our 5 phyla. Roger, I am a little saddened that your name doesn’t contain a “p.” After all, the funniest of all the phyla starts with a “p.” So we’re going to do it as a bonus.

Priapulida:  means “little penis.” I mean, just look at them.

Priapulia

Have a nice day!

i'm winging this one

I feed a Red-tailed Hawk everyday. When I first started several months ago, he wouldn’t even eat with me in the room. No matter how hungry he was, even if I put his food on his foot, he would not budge. After about four months of patience and persistence, he began to eat in front of me. Then, he took food from my hand. After another few weeks, he was standing on my hand and eating from it. To me, this was the ultimate act of trust. We had finally arrived.

But then, one day, he was standing on my glove eating and began to lose his balance. He spread his wings quickly to recover, and then looked me, expressionless, in the eye. He lowered one of his wings and rested it on my shoulder and turned back to his food. He finished his meal, one wing around my shoulder for balance the whole time. I could feel his stiff primary feathers against my neck and the heat from his light but powerful wrist. That hawk choosing to put his powerful wing around me was one of my favorite moments to date.

Over the past few months, I’ve been lucky enough to interact with raptors. I’ve spent many hours staring at them, falling in love with the eyes of a Great Horned Owl, the feet of a Bald Eagle, and the beautiful feathers of the Red-tailed Hawk. But what I’ve grown to appreciate most about birds is their wings. They need explanation to really understand.

A folded wing (baykidsmuseum.org)

When a bird is not in flight, you see only a small portion of their wings. They have them folded up tight, exposing only the tip. But under those feathers are the forearm, an elbow, and a humerus. These words should ring a bell, since they are parts of the human arm as well. As evolution would have it, bird wings evolved from limbs adapted for terrestrial locomotion- aka- arms.

Wings are highly adapted arms that are specialized for flight- so specialized that they are used essentially only for flying. Somewhere in the transition between arm and wing, several big adaptations developed. A sheet of skin grew on the inside of the elbow joint, providing more surface for lift and limited motion between the humerus and forearm. This skin is called the patagium.

Comparison between human arm and bird wing

The wrist bones fused and elongated, forming the carpus (the portion that is exposed when a bird’s wings are folded). The bones of the hand reduced in number, as did the phalanges. They shifted to be in line with the carpus and lost almost all flexibility. And the feathers; we can’t forget about the feathers.

Flight feathers sprout posteriorally from the limb. The large primary feathers toward the tip of the wing sprout from the bird’s “hand” and help provide thrust, pushing the bird forward through the air. Secondary feathers are the large ones that sprout from the forearm. Their flat, boxier shape provide upward lift- not unlike the wing of an airplane.

Bone positions in an extended wing

To me, these things are not easy to understand just by looking at a bird sitting there. You have to extend the wing, fold it back up, extend it, and fold it back up several times to appreciate how the segments are put together and how the feathers fit into the whole picture.

Even in flight, it takes keen observation to understand. Most of what you see is feathers- the actual wing ends way before the feathers do. When a bird is flying, the outstretched forearm and humerus can appear to be one segment. But if you ever have the opportunity to feel an outstretched wing, you can trace the bones with your fingers and clearly feel that elbow joint. It’s there, disguised by feathers and that tricky patagium.

After studying a bird’s wing, it will make you want to cut the Wright Brothers a break. The complex and precise design of a bird’s wing is a tough thing to replicate for us clumsy humans. I think we’ll have to leave graceful flight up to the birds and their elegantly evolved arms.

your lanula is showing

This one time, my toenails fell off.

My dad and I had gone on a backpacking trip and I committed the rookie mistake of not breaking in my new hiking shoes first. Also, I wore tissue-thin socks like a jerk and didn’t cut my toenails short enough. The entire first day of the hike was downhill into a valley, and by the time we set up camp, both of my big toenails were barking. By the end of the week, they began to turn blue. Flash forward a few months, and they fell off. Klink klink, right onto the floor.

Now, I’m sure you’re wondering why I shared that all-too-personal story with you. I shared it with you as an opener to today’s topic: the exciting world of keratinized structures.

Keratin is a fibrous protein, one of the three major classes of proteins. Keratin is the major protein component in hair, nails, feathers, scales, horns, and a variety of other epidermal structures found in vertebrates. Within the field of anatomy, you hear these types of structures referred to as “epidermal outgrowths.” As you can surmise, this means that they originate from the epidermal tissues and can be heavily modified for different species.

Sometimes these structures arise as a means of sexual display, like big horned sheep that butt their gigantic horns for sexual rights to females. Feathers have many functions, some of which include thermoregulation, sexual display, and flight. Hair in mammals is primarily for thermoregulation. Claws are generally for foraging and defense. Scales help to protect reptiles’ bodies like armor. How do our weird little fingernails fit in to all this?

Our nails evolved from claws. Our mammal ancestors walked on all fours and foraged with claws. As the primates began to branch off and perform dexterous tasks with their hands, claws became cumbersome. Fingernails were the evolutionary solution to this problem; they protect the supple fingertips and help to perform very tiny tasks, like removing splinters.

The nail plate is made up of several layers of dead cells, the remainders of which are almost entirely keratin. It is curved so that it covers the terminal segment of your finger in a way that protects the soft nail bed underneath from damage and impact. The lanula (the half-moon shaped thing at the base of your nail) is where live cells are that produce the nail plate.

Sometimes, as a result of traumatic impact, the nail bed is damaged so badly that it separates from the nail plate, which will eventually fall off. Luckily, that little lanula will keep on working and grow a new nail plate over the course of a few months. Trust me, I know. 

an ant rant

Ants have a three-tiered social system. You have the queen, the male concubines, and the all-female working class. The queen has one duty and one duty only: lay eggs. The “male concubines,” or drones, are responsible for knocking up the queen. And the workers must take care of all the rest. They feed the babies, build and repair the nest, defend the colony, and wait on her majesty.

There can be multiple queens per colony, but usually just one. She is fed by the workers and lays eggs. These suckers can live for up to 20 years- longer than either the drones or workers. A queen can lay eggs from a single mating for several years. In a single lifetime, a queen can give rise to millions of ants.

The drones are the only males of a colony, and pretty much just eat and have sex. They really have the life. That’s pretty much it for them.

The worker ants are sisters- all sterile daughters of the queen. They take care of their little sisters from the time they are eggs to emerging pupae. They carefully move them from nursing chamber to nursing chamber as they go through the stages of being an egg, larvae, and pupae. They also maintain the mound by expanding, building, and maintaining the hallways by spitting on the walls for structural support. Furthermore, they do all the foraging. The sisters find food, bring it back, and organize it into a stash for the entire colony. A subset of super beefy workers- called soldiers- are in charge of defending the nest from invaders or adverse weather.

When an ant dies, her sisters will drag her little body out of the nest, as far away as possible. They do that as though they are following hospital protocol, aware of the biohazard of a degrading body or the increased possibility of disease present in that deceased ant. One experiment from a while back sought to isolate the hormone that is secreted at death, so the scientists took dead ants and rubbed them all over live ones. I bet it was pretty funny/horrible watching the unwilling test subjects being dragged out of their nest by their instinct-driven sisters.

All hymenopterans (bees, ants, and wasps) operate using a haplodiploid reproductive system. To be haploid means to have only one set of chromosomes. Diploid means to have two sets of chromosomes. You, human, are diploid, since you have two sets- one from your mama and one from your daddy. Depending on whether you’re a boy or girl, your sperm or eggs are reduced by one half so that they are haploid. That way, one haploid sperm + one haploid egg = one diploid baby.

But with ants, it’s a little different. A queen lays both fertilized and non-fertilized eggs. Unfertilized eggs develop into haploid male drones, and fertilized eggs develop into diploid female workers.

These workers share 75% of their DNA, which is clearly more than the typical 50% that human siblings share. They have their haploid drone daddy to thank for this. Since he only has one set of chromosomes to offer them, they all get the exact same set of genetic material from him. They have a 50% chance of getting either of mom’s sets of chromosomes. Add this all together, and the sister workers are on average 75% genetically similar. (Sister power! See below figure.)

The distribution of genetic material in a haplodiploid system. Each "x" represents a chromosome.

Now, you may be wondering how inbreeding is avoided, since the only males around seem to be the disturbingly genetically similar queen’s sons. But an adaptation has evolved to keep this from happening: wings. Both queens and drones are born with wings. Upon reaching maturity, drones will fly away from the nest and find a new queen to breed. Meanwhile, worker ants selectively beef up a few female larvae here and there by feeding them more nutrients… and spitting on them… to produce new queens. When a little queen is ready, she’ll fly away and shed her wings after she breed. She establishes a little nesting site and boom- a few generations later, you have a new colony. Genetic dispersal is at it again…

How would you characterize a female ant from a male ant? Their sexy bits don’t matter, since the workers are sterile and essentially androgenous. Whoever guesses the gender-determining factor in a haplodiploid system gets to choose A.) to pick the topic for the next post B.) a personalized poem written by yours truly to be featured on the blog.

Hint: I already gave you a hint in the previous sentence. Don’t be greedy.

how to ruin your crustacean karma

A few weeks ago, a local Alaskan was kind enough to drive my coworkers and me up a mountain to a particularly scenic spot that is hard to get to. I rode in the backseat, and within the quarter mile up the mountain, was overcome with my first-ever bout of (severe) motion sickness. The only relief was to close my eyes and try to think happy thoughts of kittens and Anthropologie. I never saw that scenic spot, unfortunately. But I did leave my lunch, which I had eaten 2 hours prior, on the roadside. It happens.

This experience caused me to recall an experiment where an ingenious but somewhat evil scientist discovered the mechanism by which most invertebrates sense up from down. Let me explain.

In the late 1800’s, people observed newly-molted crawfish picking up small rocks and particulate from their surroundings and placing them in little cavities in their heads (called statocysts).  In 1893, a zoologist by the last name of Kreidl decided to solve the mystery behind this strange behavior. His hypothesis was that it functioned in balance or orientation, so he came up with his malevolent plan.

Kreidl placed newly-molted crawfish in terrariums with iron filings at the bottom instead of sand. As predicted, the crawfish placed the iron filings into their statocysts. And then started the fun.

He took an electromagnet and brought it close to the crawfish. When the magnet was brought close to the animal’s right side, the crawfish tried to turn over so that it’s belly was facing the magnet. Vice versa when the magnet was exposed to the left side. When held right above the crawfish, it tried to flip over onto its back. Clearly, the crawfish associated the position of the iron filings within their statocysts with the direction of gravitational pull. Ah hah!

When at rest, the ventral setae are excited.

But there’s more to this story than simply acclimating towards gravity. The inertia of the statolith (grain of sand, rock, iron filing, whatever) can also tell the crawdaddy which way it is moving. If the posterior setae are excited, then the animal experiences the sensation of moving forward.

When scuttling forward, the posterior setae are excited.

In Kreidl’s experiment, the animals showed general disorientation when the magnet was brought to the posterior. This is likely because they weren’t locomoting forward, but still felt like they were moving forward. They were all “what the hell?!” and started flipping around, searching for the sensation of gravity and rest.

Come to find out, every time a crustacean molts, it loses the lining of the statocysts and therefore the statoliths within. This explains why the statolith-gathering behavior is observable after molt. How strange this is to me: physiology dependent upon the addition of external objects to a sensory system, i.e. having to stick rocks in your head every so often. Strange, but pretty neat.

But seriously, those poor crawfish- if only they had more sophisticated cognitive abilities and inner ear complexity, I’m sure they would have felt about like I did on that mountain. If Kreidl had a mustache, I bet he twirled it and laughed the whole time.

In reality, Kreidl was not evil but super smart. His experiment was a seamless and inspired piece of scientific work. Well done, Kreidl.

Resume petting your evil cat.           

shedding light on bioluminescense

To me, one of the most horrific environments to imagine is the bottom of the ocean. It’s completely foreign and black, it’s miles from the surface, it’s under water, it’s highly pressurized, and there are scary ass animals. Among them, the deep-sea fish: most of which have one redeeming quality: light-up body parts. When it comes to glow-in-the-dark deep-sea fish, bioluminescent body parts are generally used as lures and so are feeding purposed.

Humpback Angler Fish. Yeah, good luck ever sleeping again.

Last week, an evolutionary baggage reader (Matt Martin, holla!) asked a thoughtful question. “How did deep sea bioluminescence evolve?” How can a consumer survive in the bathypelagic zone of the ocean, where virtually no light reaches, and life is scarce? What is a vertebrate doing down there to begin with?  How was bioluminescense even given a chance to evolve in such an extreme place?

Not very well. Luckily, the road for biolumeniscent evolution had already been paved by the time these deep-sea fishes sank from the middle depths to the deep. A gradual shift towards selection for those fish that could exist a little deeper and occupy a specialized niche began to occur. And so, they descended.

Within that shift, selection for increased concentration of luciferinases occurred, gradually turning into specialized organs with high concentration of coelenterazine and the luciferinases to light them up. Whoa, s*!# just got real. Let’s back up.

Luciferins are the key chemicals in the reactions that produce bio-light. A specific luciferin called coelenterazine has strong antioxidative properties (just like the antioxidants in blueberries and prunes- they bind free radicals and keep them from wrecking your cells. They’re good for you. Eat lots.) Way back in the day, the predecessors to glow-in-the-dark deep-sea fish had coelenterazine all throughout their bodies serving as antioxidants.

In the deeper parts of the ocean, oxidative stress is way less than it is closer to the surface. This is because 1. There is less UV exposure 2. There is less oxygen. When the ancient fish began to sink into the deep-sea consumer niche, the lessening physiological demand for coelenterazine as an antioxidant gave it the chance to fulfill the new demand for having a glowy dangly thing. So it began to locally accumulate, forming light-emitting organs. Of course, this was all very gradual. The glowy dangly things probably started off as a very dim photogenic patches of skin, but evolved into a specialized structure- technically known as an “esca.” Or a glowy dangly lure thing. Whichever.

Lots of other critters can glow, too. Plants, fungi, marine invertebrates, bugs, worms, you name it. But that’s a whole ‘nother can of… well, worms.

Here's the paper if you're feeling ambitious:

The origins of marine bioluminescense: turning oxygen defence mechanisms into deep-sea communications tools. Rees, De Wergifosse, Noiset, Dubuisson, Janssens, Thompson. The Journal of Experimental Biology 201, 1211-1221 (1998).

that tooth thang

Currently, I’m interning at a raptor education center. Basically, I show people birds and explain all the cool things about them. Some people come in and ask really good questions like “can they see in color?” or “do they mate for life?” However, some people ask not-so-intelligent questions. The other day, a young presenter was holding an Eastern Screech Owl and was asked by a guest “what is that tooth thang in the middle of its face?”

The guest was referring to the bird’s beak.

Of course, I mentally shook my head and entertained thoughts about how ignorant one must be to not know a bird’s beak when one sees it. But later on, I began to think that maybe I was being narrow-minded. Is it so dumb so register a tooth and a beak in the same category? Could the beak be the evolutionary cousin of teeth? Perhaps.

I started looking into the matter, this time with my mind set to evolution mode. When you think about it, beaks are pretty unique and useful structures. Birds have them, and even turtles kind of have them. Some are curved into a sharp points and tear flesh. Some are flattened into a bill and sift solids from water. Some are heavy-set and can crack macadamia nuts with no problem. Others are long and tubular, perfect for sticking down into a flower and licking out nectar. Though avian beaks are diverse now, it does not change the fact that modern birds came from a single common ancestor from Dinosaura. So the beak came from a single evolutionary point. That begs the questions- why, when, and how?

Lindsay Zanno and Peter Makovicky published a study in Proceedings of the National Academy of Science where they used a wide variety of evidence to figure out what therapods ate (theropods are the two-legged dino forebearers to birds). Evidence included fossilized dung and tooth marks on fossils (remember what fossilized poo is called?! Brownie points!). They found that early therapods were largely herbivorous, but some later evolved to be omnivorous and eventually carnivorous.

Come to find out, beaks emerged FIVE separate times within Therapoda. The diverging phyla of little herbivorous dinos experienced the drift towards and pressure for omnivory, which favored selection for having a beak. One lucky lineage went on to spawn our friend Archaeopteryx, and consequently, all of the birds both past and present.

The real kicker here is that these early beaked creatures still had teeth. I entertained this lady’s question thinking that perhaps the beak arose from the same germ cells as the teeth. But no siree, teeth were still present within the beaks. Therefore, teeth are not the structural forbearers to the beak. Not even on a germ line level.

If the lady who asked about the owl’s beak was asking because she thought maybe the beak was the product of increased selective pressure for a ripping mechanism over grinding teeth, like herbivorous therapod forebearers had, then that question was pretty good. Bravo.

But judging by her description of the beak as that “tooth thang,” my first instinct was right. That lady asked a really, really, dumb question.

polo blue and sloth poo

Instead of writing the usual first paragraph of lazy bloggers that apologizes for “not writing for so long” because of “how busy” I’ve been, I’m going to spare you the crap and go ahead and jump right in to a related (yet actually interesting) topic: sloths.

Sloths are the poster animals for laziness. They move really slowly and spend their entire lives in the trees. They exhibit few behaviors aside from eating, pooping, and mating (doesn’t sound so bad, I know). While they themselves are exceptionally interesting, they really do not possess any exceptional senses. Their eyesight is so-so. Their hearing is “good-enough.” Their sense of smell is existent but not super sensitive. You could say their most extreme qualities are their cuteness and their ability to hang on to stuff.

These solitary animals move so slowly that they rarely encounter each other. After leaving their mothers as babies, they begin to disperse and live by themselves. Adult sloths are spread throughout the jungle, slowly lumbering around in the trees unable to hear, see, or smell other sloths. Which is fine (and even nice, if you are one who prefers sloth bachelor-hood) until it comes time to fulfill that little ole’ purpose for existing. How do sloths find each other when it comes time to procreate?

They have really, really, smelly poo. So smelly that all the animals within a few square miles can smell it. A frisky sloth will slowly make its way towards the smelly, pheromone-laden poo until it encounters the poo or the maker of the poo. And chances are the maker of the poo isn’t that far away from the poo, seeing as they move at the speed of, well, sloths.

Can you imagine having to smell your way to a potential mate by… their poo? Thank goodness humans don’t function like sloths in this regard. I definitely prefer sniffing out Ralph Lauren Polo Blue or Very Sexy For Him 2. Just sayin’.

P.S. I am sorry for being such a sloth of a blogger. From here on out, I promise to write with the determination and motivation of a sloth trying to find another sloth’s poo. Sloth’s honor.

i don't know nothin' bout birthin' no porcupine babies

Let’s just dive right in. How much must it suck to birth a porcupine?! Yeah, bet you never thought of that before.

Luckily, nature has addressed this issue. But for suspense, I’ll save the solution to this prickly problem for the end. First, let’s cover a little background knowledge about our splintery mammalian cousins.

Porcupines are big rodents, kind of like beavers. In fact, a porcupine’s front teeth are just like that of the beaver. They are found in North America, concentrated in Canada and Alaska. Their rumps are covered in quills that lay down towards the rear. When the porcupine becomes agitated and feels the need to defend itself, it bows its back up like a cat. Its quills raise up in a primed a ready position. 

Quills are modified hairs that are reinforced with lots of stiff keratin. They can grow in clusters or can be evenly spaced out, depending on the species. Quills are embedded in the muscles directly beneath the skin. Since the quills are akin to hair, they can fall out as part of a natural replacement cycle, or they can be pulled out by force. These lethal weapons conjure images of blood and strike fear in the hearts of people, making the porcupine one of the most misunderstood animals around.

Being attacked by a porcupine and ending up with painful quills sticking out of your flesh is a highly improbable event. Porcupines are slow and lumbering creatures. Moreover, they cannot shoot out their quills. If an animal sees a porcupine as prey and throws its own body upon it in an attack, quills will become lodged in it. But a porcupine has no ability to shoot out its quills like Spiderman does spider webs. When you combine this revelation with the fact that porcupines cannot chase you down, the only thing you have to worry about is accidently stumbling upon a porcupine. And if that happens, well, it’s just in the cards.

Now let’s reveal the secret behind birthin’ porcupine babies. First of all, a porcupine baby is called a porcupette. And thankfully for porcupine mamas, porcupettes are furry little fluff balls. Their quills are present but not yet hardened. The keratin hardens within the first few weeks of life, making the birthing process not too horrible. Evolution gave mama porcupines a break on this one, thank goodness.

And now, let me leave you with some pictures of porcupettes. 

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