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.