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!