Pycnofibers? Or trichomes?

27 Dec

Pycnofibers and trichomes

Before dinosaurs and birds, other creatures like pterosaurs lived on the Earth. They didn’t have hair or feathers. But they had surface filaments on their bodies that can be seen in their fossils. The cellular structures are called ‘pycnofibers’. They had a single empty cylinder inside each filament. Pycnofibers arose from the epidermal cells, not from under the skin like hairs with their hair follicles. Nor like feathers. 

What amazes me, and which I find amusing, is that plants have these structures, too. They are called ‘trichomes’, and are well documented, including electron micrographs depicting the variety of trichome structures and shapes. Yet, nowhere in the literature that includes ‘pycnofibers’ is any mention of trichomes! Perhaps pycnofibers are the animal equivalent of the plant trichome. 

Trichomes can be inert with no chemical activity, or metabolic. Some are single-celled, some are multi-celled. Some are metabolic, some are secretory. Some are visible with the naked eye, others require a microscope. There is even a ‘trichom-ome’ now; the investigation of all the proteins and pathways involved in producing trichomes and their contents. Yet, the content of some trichomes is only air. And I am pretty sure that some of you have had encounters with trichomes. 

A trichome encounter

Last summer, while conducting a waterfowl breeding survey, I had an intimate 18BFAB09-FEA8-4FAA-B7BA-018F7A48EF2Cencounter with trichomes. The route for the survey was a walk-through on an unmowed dike dividing two marshes. Much of the vegetation – mustards, and other composite plants- was over my head at 5 feet plus four inches. The route was like pushing through jungle vegetation. One hand held my notebook and pencil and the other hand and arm pushed vegetation aside. 

Three-quarters on my way back to the starting point, my left hand and wrist began burning, like dozens of bites by fire ants. When I reached the vehicle, both hand and wrist were burning, red, and itching like crazy. Good thing I always wear long-sleeved shirts.

The culprit was the trichomes on stinging nettle plants. These tiny hair-like structures are on the stems and undersides of leaves. The thin outer portion of the trichome is silica, and it is very brittle. Shaped like a long hair with a fine point, the tip can break off and penetrate the skin of an animal that brushes up against it. When broken, a complex mixture of chemicals inside the trichome is dumped onto and into the skin. 

A chemical analyses reveals that those trichomes contain neurotransmitters: histamines, acetylcholine, and serotonin. Several acids are also in that mix: formic acid (remember my reference to fire ants?), oxalic and tartaric acids. One or more of these compounds can elicit pain or itching. But the cocktail of all those compounds may be the synergy to induce long-lasting pain, itching and inflammation. 

Over the next week, my hand and wrist swelled so much I had trouble moving my fingers and closing my hand into a fist. I had to switch my watch to the right wrist. I usually held my lower arm up, bent from the elbow. If I didn’t, the wrist and hand throbbed in addition to burning and itching. Twice-daily applications of a dermal corticosteroid somewhat alleviated the symptoms, but not enough. Ice also helped, but I couldn’t keep ice on it 24/7. A phone call to urgent care recommended trying an oral anti-histamine and applying a dermal anti-histamine, with icing once every hour if possible. I added a dose of ibuprofen twice a day. The pain subsided before the itching, which was the hardest symptom to  to ignore. 

Why trichomes?

With that anecdote in mind, you may guess the function of some trichomes and why many plants evolved these dermal structures. Not all trichomes are bad, however, Some are merely hair-like, with pigmentation, and cover the leaves. They are inert; no compounds are inside their trichomes. Their functions may be to trap rain and morning dew to cool the surface of the leaves and stems, or to reflect light away from the surface. Many plants in arid climates have these types of trichomes. 

If you do a Google search on ‘trichome’, the most prevalent result is photos of marijuana trichomes. Trichomes on the stems and leaves of hemp plants, including marijuana, are highly evolved deterrents against herbivory by animals. The three different types of trichomes of Cannabis sativa, or marijuana, are “the very factories that produce the hundreds of known cannabinoids, terpenes, and flavonoids” that the plant is known for. Some trichomes -those that look like tall-stalked, bulbous mushrooms- have higher concentrations of the above compounds and cover specific tissues on the plants: the calyx of the flower buds. When crushed, they exude a sticky, odiferous resin that often repulses animals from eating them, except for humans. 

Why did Mesozoic pterosaurs have pycnofibers? Were their pycnofibers the animal version of plant trichomes? Possibly.  A question is, which evolved first? 

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What is the story?

19 May

This book should be required reading for all scientists, new and old. No exceptions.

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Bunny Blankets

8 Apr

A bunny in bear’s clothing? Yes, it is. A team of researchers in China developed a fabric that mimics the fur coat of a polar bear. A live rabbit was wrapped in a ‘blanket’ made img_6854-1of this prototype fabric and used infrared imaging (thermal imaging camera) to measure the difference between the rabbit’s body and ambient temperatures. The body of the rabbit under the blanket was almost completely undetected. Where the body was exposed to the changing temperatures (14-104 degrees Fahrenheit), thermal imaging detected only those exposed areas. This demonstrates good thermal insulation.

Like the fur of polar bears, the fabric also reflects infrared light. The blanket fabric reflected light up to twice that of commercial textiles and can’t be detected by night-vision scopes and cameras, just like polar bears.

What makes polar bear’s fur so special? A fiber from the fur of a polar bear is a

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Polar bear fiberS

simple cylinder. The interior core of the fibers are hollow, which helps traps their body heat and insulate them from Arctic winters. This hollow trait of the bear’s fibers also reflect back infrared light, but the transparency of those same fibers scatter UV light to neighboring hairs, via light scattering. Their black skin absorbs and stores heat from that UV light. All these factors help insulate the polar bear from cold, even when wet. Think of passive solar energy and storage.
Despite being so porous, the fibers are strong because a thick layer of keratin surrounds the hollow core. Keratin is a protein common in nails and hair. Keratin protein molecules form a helix, and two keratin helixes wind around each other conferring both strength and elasticity. You can think of animal fiber as a thick rope containing many stings of these entwined keratin filaments. In the case of the polar bear, these keratin layers surround the hallow core.

So how did those scientists mimic the fur of a polar bear? They did so through a very complex process of spinning a mixture of compounds found in silk and crustaceans (like shrimp and crabs). A solution of fibroid, a protein in silk, and chitosan, a structural carbohydrate made from chitin, was spun in freezing conditions. Ice particles separated the fibers leaving air spaces when warmed. These resulting fibers, which had both properties of thermal insulation and strength, were aligned and then woven into a fabric, and tested on the bunny.

Being a fiber artist, I wondered how fibers from sheep compare to the properties of polar bear fibers. The variability of fiber between breeds and individual sheep is immense. So many factors influence the characteristics of wool fibers: breed, age, nutrition, and weather. However, the primary composition of wool fibers is fairly consistent.

Because I raised sheep in Oregon (decades ago) and spun their wool, I was familiar with the overall structure – overlapping scales in varying lengths – of wool fibers. However, I wanted more details on its morphological structure. I can quickly draw and label the structure of muscle fibers and fibrils, but not a wool fiber! So I searched online for a diagram and electron micrographs, longitudinal and cross-sectional,  of a typical wool fiber. From these we can see how polar bear fibers are structurally different, but they both have insulating properties.

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Mammal, silk, and plant fibers

Most animal fibers contain exterior scales (except polar bears,  remember). You can see the difference in scales, or lack of, in the image to the right, in both animal, silk and plant fibers. Also apparent are the sizes of the scales, and their distance apart. These are the images most of us are familiar with when we think of fiber structure. But it’s more complex than this.

If we compare the fibers in this image to that of the polar bear fiber, we can see that fiber structure of wool is more complex. You don’t see slightly rough exteriors and hollow centers! Instead, wool has irregular and overlapping scales. But that’s not where the differences end.

Let’s look at the interior morphological structure of wool. Wool fiber contains three

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Morphological structure of a wool fiber.

primary parts: the outer cuticle, the cortex (divided into two sections), and the medulla. The cuticle includes the scales and several layers that surround and protect the cortex.

The cortex is the bulk of a fiber. In that cortex are many macro- and microfibrils, similar to a muscle fiber. A similarity to the polar bear fiber, and that of most mammals, is keratin. The medulla is not really distinct, depending on the mammal species. It is empty space and arranged in a honeycomb fashion within the cortex. That space can be tiny, as in sheep breeds with fine fiber, or larger, which is more typical in medium and coarse fiber breeds.

The structure of the wool fibers, and the fiber ‘community’ (meaning the collective grouping of fibers in what we sheep folks call ‘fleece’), contribute to the insulating properties. Another structural component is fiber crimp. Wool fiber can be long and straight, or short with many crimps. The number of crimps, how they are spaced along the length of the fiber, and how close they are to neighboring fibers, greatly influence how much air a fleece can hold within it. That air also contributes to its insulating properties.

But it doesn’t stop there! At least for humans that shear those fleeces, wash and prepare them to spin into yarn that is eventually knitted or woven into fabric to wear or for other domestic purposes. The natural structure and characteristics of those fibers determine how we process the fleeces, how we spin them, use the yarn for a final product.

We could even knit a blanket for a bunny.

Writer’s Block

27 Mar

I really need to get rid of this block. CA595853-ED63-47D8-9C69-FBBAC89A0B8D

2018 Year of the Birds

8 Feb

Like Jonathan Franzen (author of this article), birds were just simple pleasures in my life until my fourth decade. Watching groups of evening grosbeaks chatter and bully each other in the large feeder outside my cabin’s picture window was often the amusement of my winter days in Maine. As was observing parental red-tailed hawks on fir tree branches teach their fledglings to fly by taunting them next to the pastures in Oregon.

Thinking back, the enchanting swans in the fog that occasionally visited the small ponds of spring melted snow in the field next to the house I grew up in, the majestic snowy owl that often perched on a large tree branch in our back yard looking at me while I sat in my snowsuit and looked at it……. These are still vivid memories that probably contributed to my path to become a biologist so many decades ago.

Learning about their evolution (and ties to dinosaurs), their adaptive biology and physiology, the unique complexity of colorful plumage, the often amusing social interactions with each other and within their ecosystems, their impressing tenacity to migrate thousands of miles, their inherent traits that we covet as amusing (such as the burrowing owls clownish movements), and even ornithologist’s taxonomy, which reveals more about ourselves than the animals; it all deepened my respect and wonderment for the world of birds.

Now, in my retirement and no longer in the whirlwind of academic life, birds have become more personal and intimate, which has increased my passion for them. Holding a six-week golden eagle nestling while working with two USFWS biologists to band and collect data was like holding an angel in my hands. Bird surveys allow glimpses into aspects of their lives: breeding, migrating, feeding, competing, parenting, and housekeeping. Handling birds while banding them with metal ‘bracelets’ is more than just data collection; it is a rare and privileged opportunity to share a moment of respectful interaction between bird and human.

This winter by a lake in west-central New York State has provided me with the same fascination and enjoyment of my childhood. Instead of purposeful counting, naming, banding, and poking, I have been simply a bystander observing and enjoying that simple delight. When the small group of four trumpeter swans expanded to 19 swans, I was out on the edge of the lake with binoculars searching for them every day. When an adult bald eagle swerved down from the air to instantly grab a fish from the water barely 25 feet from the side of my kayak, I was a giddy kid again. Watching the antics of house finches play hide and seek in the weeping elm tree next to the deck made me smile and laugh. While I stood on the edge of the Genesee River gorge this past fall, a male American kestrel flew and kited below me with the sun gleaming off its blue feathers. It was like watching a ballet in the air.

Many people share a passion for birds. For some its about ticking off names on lists, some fans have favorites and spurn other non-favorites, others travel around the world to see exotics, and many colleagues think about them mostly when they are a component of their research. Others delight in watching birds out their windows, and I know a few that give them their own names. Many avid birders organize and participate in bird watching groups, which sometimes amusingly reminds me of bird social behavior.

We all have our own source of what birds bring to our lives. And there is a growing number of us that work towards improving the world in which birds live. In today’s human-contructed world, we attempt in diverse ways to protect them from disappearing. Part of this mission entails educating people on how wonderful and important birds are, part is “boots on the ground” activism, such as volunteering with groups that rescue and rehabilitate injured and orphaned birds, or participating in bird counts that provide numbers from which we can estimate populations and movement. The importance of the latter is information to help us manage and improve habitat for birds.

This year is dedicated to the birds. Learn about birds, all birds. Let birds expand your world and share it with others. You don’t even have to learn their names. It’s just that simple.

Happy Anniversary Plate Tectonics!

5 Dec

Fifty years ago, the ideas of plate tectonics crashed into the earth science arena. First proposed in the early 1900’s by Alfred Wegener, the hypothesis that continents drifted around the planet like floating icebergs was naysayed. He could not explain how or why.

In 1967, while many of us were wearing flowers in our hair and inciting a revolution, Dan McKenzie and his colleague Bob Parker at Scripps Institute in California (and independently, Jason Morgan at Princeton Univsersity) put together pieces of the puzzle and described how plates move and continents drift. They started their own revolution.

Geology was changed, like a volcano erupting in the field. Not only does geological evidence confirm plate tectonics, but also biological. Fossils of some species of plants and animals are located within specific areas on continents where they adjoined each other. Those continents are now separated by thousands of miles of ocean.

Plate tectonics and continental drift have awed me since I was a child. I have no idea why, except that they are like a memory of deep time. And seeing examples and remnants of plate tectonics and continental drift is like looking at old family photos. I’m captivated.

In honor of the anniversary of plate tectonics theory, follow the link to a poem I wrote years ago. Ode to Plate Tectonics.  Meanwhile, enjoy your daily ride on your continental plate.

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Sagebrush

12 Mar
Sagebrush.

Its aroma is almost an aphrodisiac.

It is the timeless scent of an ancient organism
that evolved with the sand and deserts

of the Great Basin.

Many of the Artemesia spp. are very aromatic; their leaves lush with terpenoids. These aromatic lipids are volatile and will relinquish their scents when leaf cells are crushed, or even under the right weather conditions.

Adding to the symphony of volatile compounds are the three isoprene rings that build the  sesquiterpenoids; lactones that repel herbivory, invite the sagebrush checkerspot butterfly to lay their eggs, and gall midges to build galls to house their nymphs.

But they also attract humans that cherish the yin and yang of their leaves and scent. The silver hairs, the trichomes, on the leaf surfaces that catch the sun and dew; the aroma they impart when crushed between fingers, the scent when scattered upon a fire.

In a harsh land where sun and sand cover the earth,

in the shadow of the mountains,

sagebrush provides shade for sage grouse,
structure for fly nymphs,
caterpillar homes,
and an aroma that
sits
and
waits
between the fingers
of the Ancient Ones.
Sagebrush,
all Artemesias,
are my spiritual plants.

 

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