Harker Bio: Evolution's Wonders

The Golden Silk Orb-Weaver: A Natural Architect

2009-03-26T22:20:00.000-07:00

Nephila clavipes

The genus Nephila are masters of architecture; derived from the Greek words nen(thread) and philos(love), their name epitomizes theis spinning skills: they have the strongest, best silk in the world, are skilled designers and builders, and have effectively made anything that can fly through a forest their oyster. From the equipment to the material to the design, they've got it all. They can rebuild its web perfectly every day in about an hour. Their silk has been used to lead a severed neuron through the body back to the site of injury.

General Characteristics:

Nephila clavipes are part of the Arthropod subphylum Chelicerata, which includes scorpions, mites, and spiders. While the male is a rather uninteresting brown and about 5 times smaller than the female, which has yellow and red stripes and spots and can grow up to 4 cm in length. It is the female who does all the extensive and elaborate web-building, while the males essentially just sit around about 5 cm above her, waiting for food and sex. She, on the other hand, stays quite busy building and repairing her web and wrapping and eating her food, using venom to paralyze it as she does so. Talk about gender inequality...

A golden silk orb-weaver's web

The Web:
Besides building and repairing their web perfectly in one hour every day, Nephila webs are built to last for 2 years, stretch to over a meter in diameter. In addition to the fine mesh orb seen above, she constructs barrier webs that protect the web from weather, birds, and other larger objects and also function as an alert to invaders and prey smashing against the web.

Furthermore, she may also install zig-zag lines of structural silk to increase stability or open a hole to allow wind to blow through without destroying the entire web. A special feature of golden silk orb-weavers is their yellow color, which has been shown to act both as an enticement for flower-seekers like bees and as camoflauge in shady areas with mottled sunlight. She may incorporate more or less yellow pigment in her silk depending on light conditions in the area, revealing a rather complex and cunning mind behind that pretty body.

Silk gland spigots

The Silk:
First of all, all silk is not made equal. Both the ingredients and the process differ, and Nephila clavipes, among others, can spin up to seven different kinds of silk, each with unique properties and purposes in its web.
With a tensile strength of 4×10⁹ N/m, their dragline silk is six times stronger than steel and 10 times more effective than Kevlar at dissipating energy, it has a plethora of potential uses, from parachutes, bullet-proof vests, and ropes to sutures, tendons, and ligaments.
One excellent example is the use of Nephila clavipes dragline silk in nerve guidance. Besides being incredibly strong, it is not only nonimmunogenic but also has antibacterial and antifungal properties. Furthermore, its structure promotes cell migration and adhesion and can even obtain its own myelin sheath in the presence of human Schwann cells. You'd think it was meant to be.

So how on earth do they do it? Think of silk making in terms of steel manufacture: in order to make it, you need not only the iron but also the Bessemer process to transform that iron into beautiful, powerful steel. Silk works in much the same way. Spiders have both the proteins to make it and the tools to transform them into long, strong silk. We, on the other hand, only have one of the two: the material (for now, anyway).
Using alternating parallel molecules and random-ordered regions, spider silk is able to contract or expand according to pressure, thus enabling both flexibility and strength.
Biomimic Garry Hamilton elaborates, "A single spider-silk thread can be as small as one micron (i.e., one-thousandth of a millimetre) in diameter. The protein chains that form the threads are roughly another 1,500 times smaller still. What scientists suspect is that during spinning, the spider exerts a force that causes microscopic fistfuls of these protein chains to bend back on themselves and align with one another to form tiny crystals. These crystal chiplets, containing thousands of neatly arranged amino acids, apparently prevent microscopic cracks and hold the silk together....there's not an overabundance of crystal, thereby limiting the silk's density and maximizing elasticity."
This allows Nephila dragline silk to combine incredible tensile strength with elasticity up to 40% of its original length. In contrast, capture silk trades rigidity for serious flexibility by implementing spiral structures that allow for 300% extension to snag insects flying at high speeds without breaking.

Nature's architects are the best of the best from hundreds of millions of years of development, and we have a lot to learn, if we're willing to listen.

-Vishesh Jain

Image Sources and Cool Links:

Images:
Keith Ramos - Golden Silk Orb-Weaver
Discover Life - Golden Silk Orbweaver
Wikipedia Commons - Nephila Clavipes - Merritt Island
Dennis Kunkel Microscopy - Spider Silk Gland Spigots
Protein Spotlight - Nephila Clavipes (Frank Starmer)

General:
Featured Creatures - Golden Silk Spider - Nephila Clavipes
Animal Diversity - Nephila Clavipes

Web:
New York Times - Crafty Signs Spun in Web Say to Prey, 'Open Sky'
YouTube - Nephila Clavipes. Golden Silk Spiders
YouTube - Nephila Weaving Circumferential and Radial Fibers

Silk:
Health Hinge - Spider Silk Fiber of Nerve Guidance Conduit
World and I - Artificial Biomaterials
Equinox - Stealing Nature's Secrets
Protein Spotlight - The Tiptoe of an Airbus

The Velvet Worm: An Evolutionary Enigma

2009-03-21T17:39:00.000-07:00

Dating back to over 540 million years ago, velvet worms are lost in a mysterious fog in terms of their exact place in phylogeny with respect to arthropods. Apparently worms with legs, Onychophora are an evolutionary nightmare. Treated for years as a missing link between annelids and arthropods, new research from 2006 reveals a closer association to the latter, particularly Chelicerates.

Skin of Wambalana makrothele

In particular, their brains share remarkable similarities to spiders, and as one biologist points out, "The animal looks simple, but the brain is not simple. Onychophora have pretty complicated behaviors. Colleagues in Australia have discovered that they have fascinating rivalry behaviors, interesting group behaviors and group interactions. Their ecology and genetics are fascinating, and they have really weird sex." The presence of such a developed brain so early in evolutionary history could lend serious insights into the development of the brain itself. What's really bizarre is that although velvet worms have striking similarities to spiders within their heads, at that point all resemblance ends.

Euperipatoides rowelli

Except for one thing.
While spiders shoot silk, velvet worms shoot stringy goo.
Admittedly, velvet worm slime is far from silk molecularly, and spider silk departs from spinnarets on their abdomen while velvet worms use oral tubes. Nevertheless, the slime is amazing. Without congealing within the worm's own body, the slime is still a quick-hardening, sticky substance that sprays from two oral tubes, intertwining and lacing over its prey. This substance does not adhere to the water-repellent skin of the velvet worm, which can therefore safely approach its victim, bite a hole in its skin, and suck out its vital systems after digesting them with powerful saliva.

Here's a Spanish video of a velvet worm capturing and eating a small beetle.

The elegant Nodocapitus inornatus

If you're still curious about that "weird sex," velvet worms use spermatophores, or packets of sperm, to transfer the male gametes to the female. Now this is weird enough, but there are several arthropods that do it too. What really begs explanation is that the spermatophores are transferred from spikes on the the head of the male to the back or sides of the female. Enzymes in the female's body then break down both the spermatophore casing and the female's own skin, allowing the sperm to flow through this self-inflicted wound to her reproductive organs. For one reason or another, the wound usually escapes infection, and velvet worms have apparently been successful enough to survive hundreds of millions of years without modification. Velvet worms give birth in a variety of forms, ranging from oviparous(egg-laying) to ovoviviparous(egg-hatching within the body and then live-bearing) to viviparous(live-bearing). Weird.

A velvet worm crawling all over a leaf

-Vishesh Jain

Image Sources and Cool Links:

Images:
Wikipedia Commons - Velvet Worm (Thomas Stromberg)
Australian Museum - Wambalana makrothele (A. Reid)
Australian Museum - Nodocapitus inornatus (J. Norman)

Evolution and Phylogeny
Science Daily - Petrified Velvet Worms from 425 Million Years Ago
Bio-Medicine - Velvet Worms Reveal Secret Sisterhood With Spiders
ABC Science - Velvet Worms Spin Web of Intrigue

General
Australian Museum - Velvet Worms
Wet Tropics - The Velvet Worm
YouTube - Onicoforo cazando luciernagas
YouTube - Costa Rican Onychophora

The Peregrine Falcon: Fastest Animal on the Planet

2009-02-19T22:45:00.000-08:00

Peregrine Falcons are raptors with keen eyes, strong wings, powerful beaks, and tremendous speed. Outside their nesting season, peregrine falcons earn their name by traveling extensively, as much as 15,500 miles a year. Once endangered by DDT and human development, they have rebounded and are now found all over the world. Though they prefer open spaces such as plains and sea coasts, they live everywhere from tundra to desert to cityscape.

Peregrine falcons are known for their speed. When they plummet to catch an unsuspecting pigeon below them, they can reach velocities over 200 miles per hour (320 km/h). That's over a fourth of the speed of sound. Zoom. But what's also fascinating about these remarkable birds are the adaptations that allow them to use such power.

The Eyes:
If a peregrine falcon is flying or perched over a kilometer in the air, as they often are, it would be useful, perhaps, to be able to see what it's trying to strike. While they're no mantis shrimp in terms of spectral range, they do indeed have some of the keenest eyes on the planet. With full color vision and rapidly focusing lenses, their eyes have a resolving power up to 8 times greater than humans, enabling them to spot prey miles away and keep track of it while approaching at breakneck speed.

The Shape:
To achieve 70 mph speeds in pursuit of prey and 200 mph plummets to attack those below, the peregrine falcon has one of the most streamlined bodies in the air. The curved wings create an air foil effect in multiple dimensions, maximizing maneuverability, lift, and speed.

The Wings:
Besides the streamlined structure of the wings themselves, peregrine falcons maximize speed in every way possible. In pursuit, it can flap its wings up to four times a second, and in its dive it is able to let gravity pull it down with negligible air resistance, locking its wings in place to create minimum drag. The feathers themselves are stiff, slim, and unslotted, allowing them to literally slip through the air as they attack. As in all birds, their wings are hollow, enhancing flight and maneuverability in the air.

The Power:
Small tubercles and bones in the nose prevent the immense air pressure from flowing into and rupturing their respiratory system. In addition to tons of strong red muscle fibers, peregrine falcons have one-way lungs, like most birds, to maximize oxygen intake. To achieve torpedo-like speed both horizontally and vertically, peregrine falcons have an enormous keel, part of the sternum. As the attachment site for flight muscles, the larger the keel, the more powerful the flight, and this makes these birds some of the fastest in the world.

The Attack:
Now, if you were to drop a couple hundred stories, you'd probably be going pretty fast too. The question, then, is whether you'd be able to catch something, halt your dive, and be in a medical condition to eat it. From the muscle, to the talons, to the beak, these raptors are serious predators. When their keen eyes finish guiding their dive into their prey, if the impact of 200mph razor-sharp talons hitting a poor pigeon's back doesn't kill it, the tomial tooth of their strong beak can break the stunned bird's spine in a second. Then the falcon can leisurely eat it in the air or on the ground, after plucking its feathers, of course.

A National Geographic video tracking a peregrine falcon's flight speeds from the air.

-Vishesh Jain

Image Sources and Cool Links:

Speed and Strike:
Extreme Science - Fastest on Earth
HowStuffWorks - How Do Peregrine Falcons Fly So Fast?
National Geographic - High-Velocity Falcons

Endangered:
Science Daily: Peregrine Falcons May Face New Environmental Threat
Royal Belgian Institute of Natural Sciences: The Return of the Peregrine Falcons
Texas Parks and Wildlife: Peregrine Falcon

General:
Cornell Lab of Ornithology - Peregrine Falcon
National Geographic - Peregrine Falcon
University of Wisconsin - BioWeb: Peregrine Falcon

Images:
U.S. Fish and Wildlife Service - Ozzie
Raptor Guide Gallery - Peregrine Falcon
TreeHugger - DDT Redux
Jerry Ting - Peregrine Falcon
Audubon - Signature Species: Peregrine Falcon

The Mantis Shrimp: Pinnacle of Evolution

2009-01-20T15:48:00.000-08:00

Overview:
What, you may ask, is a mantis shrimp? It's neither a mantis nor a shrimp, but might be what you would get if you could make J.K. Rowling-esque hybrids and pumped in a lot of magic. View at your own peril.

Mantis shrimp are essentially a true beacon of evolutionary progress. You will soon see that if a scientist wanted to prove the absolute amazingness of evolution, this would be the creature to pick. And they're not just one species, or even a genus: they make up an entire order, if a small one: Stomatopoda.
They're marine crustaceans, reaching about a foot in length, usually living and looking for food on the ocean floor, chilling out in rock formations or tunnels they build in the sea bed. They diverged from other crustaceans over 400 million years ago during the Cambrian period, so they are only distantly related to the likes of shrimp and lobsters. They mostly live in tropical waters, and can be diurnal, nocturnal, or crepuscular and have an extremely diverse diet, both of which characteristics depend on the species.

Why Mantis Shrimp?
If I were to tell you that the mantis shrimp is not just a crustacean, but a very intelligent crustacean that is long lived (monogamous for up to 20 years) and exhibits complex behavior like ritualized fighting (common in larger phyla like mammals and reptiles), excellent learning ability and memory (they can remember the individuals they meet, by sight, smell, and sound), and several modes of communication (like fluorescence, smell, sound, and visual cues), you would probably agree that this is one awesome order.

But wait! There's more!

The same organisms, the same order, that has all of these complex and highly developed characteristics, also has amazing vision. Mantis shrimp have hyperspectral color vision, allowing them to see and distinguish anywhere from infrared to visible to ultraviolet light at once. They are each separated into three bands (trinocular vision), allowing each eye to see objects from three different perspectives, giving both of them highly-developed depth perception. Their eyes, mounted on stalks and capable of moving independently, can sense up to twelve distinct color channels extending to UV, can execute both serial and parallel image processing, have up to 10,000 ommatidia (the individual parts of compound eyes) and 16 different photoreceptor types (where as humans have 4), and can distinguish polarised light (the orientation of the oscillations of the waves of light).

Before it was discovered that mantis shrimp could see circular polarized light, there were only three known modes of sight - black and white, color, and linearly polarized vision. So mantis shrimp alone occupy a quarter of the known ways of perceiving light. Mantis shrimp eyes have special filters that convert circular polarized light into linear polarized light. To humans, linear polarized light appears as glare; but for mantis shrimp, the polarized light is used in mating displays. Gonodactylus smithii is one of two known species that can see circular polarized light, finishing up all the possibilities (four linear and two polar) for polarized light and thus is the only known organism to have optimal polarization vision. There are a couple of theories as to why they developed these legit eyes, which include improved communications using the fluorescence we talked about earlier and internal processing of images within the eye so that the small brain can have some help from the rest of the nervous system.
If you don't want to read that awesome paragraph packed with so many cool facts, just know that stomatopod eyes are largely considered to be the most complex eyes in the animal kingdom.

A fluorescent stomatopod catching its prey.

But wait! There's more!

These same organisms, this same order, that has such complex behavior, intelligence, life-span, and vision also has some of the coolest weapons on the planet (just remember that these guys are violent). So mantis shrimp, as you may have guessed or seen in the pictures, have these claw-type appendages. There are two kinds of mantis shrimp: spearers and smashers. Spearers have spiny, pointy arms to skewer, snag, and generally catch and slice prey, while smashers have clubs that they use to...smash stuff.

A Californian mantis shrimp-amazingly cute.
It starts playing around with an octopus at 0:50, and starts trying to attack it at 1:55.

The raw data for their punches:
Peak speeds: 23 m/s (75 ft/s) (fastest kick in the world)
Peak accelerations: 10400 g (like a .22 caliber bullet)
Immediate strike force: 1500 N
That's one of the top fastest movements in the animal kingdom, and the fastest feeding strike.
The punch is so fast and so powerful that it creates a collapsing cavity between the claw and the victim. When it collapses, it produces sonoluminescense(a little light and very high temperatures) and an explosive shock wave. Essentially, with one punch, the prey is hit twice: once by the original (1500N) punch, and once by the resulting shock wave, which can often paralyze or even kill small prey.

How do they do it?
Using a saddle shaped structure (a hyperbolic paraboloid) in their arm cavities, they can store immense amounts of elastic energy and then shoot out their arm with tremendous acceleration, speed, and force. Considerable developments of what we know about stomatopods and the strike in particular have come from Sheila Patek, Wyatt Korff, and Roy Caldwell, from Berkeley. According to Science Daily:
"Patek is currently conducting experiments which show that the blow yields a tremendous amount of force - well over a hundred times the mantis shrimp's body weight.
In a short note appearing in the April 22 issue of the journal Nature, Patek and her colleagues, graduate student Wyatt Korff and professor of integrative biology Roy Caldwell, report the record-setting strike and the unusual saddle-shaped spring in the hinge of the shrimp's striking appendage that makes it all possible.
This spring is technically a hyperbolic paraboloid, a structure similar to a Pringles potato chip. Very strong, especially when compressed, hyperbolic paraboloids have been used by architects to create structures that don't easily buckle. The nautilus employs this structural element to build a sturdier shell. In mantis shrimp, however, the saddle-shaped structure can also function as a spring, the UC Berkeley researchers found. It stores energy until a quick release propels the shrimp's club in a shell-crushing blow.
"We know of no other biological example where this saddle-shaped structure is used as a spring," Patek said."

Here's a video of Patek presenting the stomatopod's kick to the TED conference in 2004.
A few key time points:
1:20 - types of mantis shrimp
2:30 - striking speeds
4:55 - kicking mechanism
8:55 - striking force
10:20 - cavitation
13:45 - prevention of claw deterioration

So, now you know stomatopods. One order's got it all: intelligence, complex behavior, a long life-span, Superman-like vision, and a spring-loaded hyper-punch. Evolution for the win.

-Vishesh Jain

Image Sources and Cool Links:

The Eyes:
Wired Blog - The Magnificent, Ultra-Violent, Far-Seeing Shrimp from Mars (by Brandon Keim, Image: Justin Marshall)
Wired Blog - Shrimp Eyes May Hold Key to Better Communications (by Brandon Keim, Image: Roy Campbell)
Science Daily - Mantis Shrimp Vision Reveals New Way That Animals Can See

The Claws:
TED - Sheila Patek Clocks the Fastest Animal on Earth
Trek Earth - Mantis Shrimp (Image: Rabani HMA, 2006)
UC Berkeley News - Mantis Shrimp May Have Fastest Kick in the Animal Kingdom

Behavior and Reproduction:
Animal Life Resource - Behavior and Reproduction
Flickr - Peacock Mantis Shrimp

Fluorescence:
UC Berkeley News - Mantis Shrimp Fluoresce to Enhance Signaling in the Dim Ocean Depths
Night Sea - Fluorescing Mantis Shrimp Catches Fish (Video: Charlie Mazel)

General:
Zoomr - Peacock Mantis Shrimp
YouTube - Californian Mantis Shrimp (Deep Sea)
UC Berkeley - Roy's List of Stomatopods for the Aquarium
UC Berkeley - Secrets of the Stomatopod
The Lurker's Guide to Stomatopods - Stomatopod Biology