Wednesday, August 29, 2012

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.           

Saturday, August 18, 2012

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).

Thursday, August 16, 2012

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.

Tuesday, August 14, 2012

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.