The Science of Snakeskin: Black Velvety Viper Scales May be Self-Cleaning

Posted on March 8, 2014 by Michelle Dohm

West African Gaboon viper

Whether you love them or hate them, snakes have long captivated our interest and imagination. They’ve spurred countless stories and fears, some of which may have even affected the course of human evolutionary history. We must admit, there is something a little other-worldly about their legless bodies, willingness to swallow and digest animals much bigger than them, and fangs and potentially fatal (or therapeutic?) venomous bites.

Not least of all, their scaly skin is quite mesmerizing and often laden with intricate and beautifully geometric patterns just perfect for camouflaging, regardless of whether they live high up in a tree, deep in murky waters, or on the forest floor. Snakeskin was the focus of recent research by the authors of this PLOS ONE study who sought to determine whether it has any special properties less obvious to the naked eye.

Please meet the West African Gaboon viper, Bitis gabonica rhinoceros (pictured above). Native to the rainforests and woodlands of West Africa, these large, white-brown-and-black snakes can be identified by large nasal horns and a single black triangle beneath each eye—nevermind that, because they also lay claim to titles for the longest fangs and most venom volume produced per bite. The pattern of their skin is intricate and excellent for camouflage, and the black sections have a particularly velvety appearance. These eye-catching characteristics intrigued zoology and biomechanics researchers from Germany, who decided to take a closer look.

In a previously published paper, the authors analyzed the Gaboon viper’s skin surface texture by using scanning electron microscopy (SEM), as well as its optical abilities by shining light on the snakeskin in different ways to see how it’s reflected, scattered, or transmitted. They found that only the black sections contained leaf-like microstructures streaked with what they call “nanoridges” on the snake scales, a pattern that has not been observed before on snakeskin. What’s more, the black skin reflects less than 11% of light shone on it—a lot less than other snakes—regardless of the angle of light applied. The authors concluded from the previous study that both of these factors may contribute to the viper’s velvet-like, ultra-black skin appearance.

Scanning electron microscopy (SEM) of viper scales

In their most recent PLOS ONE paper titled “Non-Contaminating Camouflage: Multifunctional Skin Microornamentation in the West African Gaboon Viper (Bitis rhinoceros),” the authors conducted wettability and contamination tests in hopes of further characterizing the viper skin’s properties, particularly when comparing the pale and black regions.

To test the wettability of the viper scales, the authors sprayed droplets of water, an iodide-containing compound (diiodomethane), and ethylene glycol on the different scale types shown above, on both a live and dead snake, and then measured the contact angle—the angle at which a liquid droplet meets a solid surface. This angle lets us know how water-friendly a surface is; in other words, the higher the contact angle, the less water-friendly the surface.

Contact angle (A) and snake skin with water droplet on light and dark areas (B)

As you can see in the graph above, the contact angle was different depending on the liquid applied and the type of scale; in particular, the contact angle on the black scales was significantly higher than the others, in a category that the authors refer to as “outstanding superhydrophobicity,” or really, really, really water-repelling. This type of water-repelling has been seen in geckos, but not snakes.

Water droplet appearance on live snake skin

The authors then took some of the snake carcass and dusted it with a sticky powder in a contamination chamber, after which they generated a fog for 30 minutes and took pictures.

Skin before dusting (A), skin under black light after dusting (B), skin under black light after fogging (C), section of SEM, showing light and dark skin (D)

After 30 minutes of fogging, the black areas were mostly free of the dusting powder, while the pale areas were still completely covered with dust. The powder itself was also water-repelling, and so the authors showed that despite this, the powder rolled off with the water rather than sticking to the black areas of snake skin. Therefore, as suggested by the authors, this could be a rather remarkable self-cleaning ability. The authors suspect that the “nanoridges,” or ridges arranged in parallel in the black regions, may allow liquid runoff better than on the paler areas of the snake.

How does this texture variation help the snake, you ask? The authors posit that all these properties basically contribute to a better form of camouflage. If the snake were completely covered in one color, it may stand out against a background of mixed colors (or “disruptive coloration”), like that of a forest floor. If the black regions have fairly different properties from the paler regions, mud, water, or other substances would rub off in these areas and continue to provide the light-dark color contrast and variation in light reflectivity that helps the snake do what it does best: slither around and blend in unnoticed.

Citations

Spinner M, Kovalev A, Gorb SN, Westhoff G (2013) Snake velvet black: Hierarchical micro- and nanostructure enhances dark colouration in Bitis rhinoceros. Scientific Reports 3: 1846. doi:10.1038/srep01846

Spinner M, Gorb SN, Balmert A, Bleckmann H, Westhoff G (2014) Non-Contaminating Camouflage: Multifunctional Skin Microornamentation in the West African Gaboon Viper (Bitis rhinoceros). PLoS ONE 9(3): e91087. doi:10.1371/journal.pone.0091087

Images

First image, public domain with credit to TimVickers

Remaining images from the PLOS ONE paper

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Can You Image That? Imaging a Cell and Its Proteins Together

Posted on October 25, 2013 by Michelle Dohm

Observing the world around us is a natural human instinct, and exploring the realm of the tiny and beautiful is especially captivating for scientists and the public alike. The business of building and testing new microscopes, and developing new methods of microscopy, is rapidly changing and evolving over time. As early as 1914, scientists started documenting the history of the microscope.

Thankfully, rather than drawing out what we see through the lens onto a piece of paper, there are now advanced forms of microscopy, like electron microscopy, that allow scientists to scan a substance—with an electron beam—to sample its topography, or surface shape, and produce wonderfully detailed images that also contain tremendous amounts of data. In a separate form of microscopy called fluorescence microscopy, fluorescent proteins—proteins in the cell engineered to have a fluorescent tag—and intracellular proteins fused to a fluorescent protein can be imaged because they emit light in response to certain wavelengths of light coming from the microscope.

In a continuous effort to “see what’s going on a bit better,” Howard Hughes Medical Institute researchers published an article in PLOS ONE today detailing improvements of their relatively new form of 3D super-resolution microscopy. It combines what they call PhotoActivated Localization Microscopy, or PALM (a type of fluorescence microscopy), with electron microscopy (EM), and lets us have a look at organelles, like mitochondria, and the location of nearby proteins, right in the same cell at roughly the same time.

For instance, if we know a specific protein attaches directly to DNA in a specific organelle, PALM allows us to see precisely the nanometer-scale location of this protein, when it is fused to a fluorescent protein. EM on the other hand, allows us to see the overall structure of the organelle, and so combining these to see both at the same time is extremely useful to cell biologists studying structure and function.

In their study design, PALM needs to be performed before EM (see image of sample preparation and setup below), and then the two images are overlaid by correlating the area of fluorescence, seen during fluorescence microscopy, to the area of the cell structure seen during electron microscopy. The overlaid image is the final result, and the goals of the researchers in this improvement study were to optimize the image resolution and the number of useable fluorescent dyes, speed up the protocol, and simplify the equipment involved by moving it from 3D (very difficult, less accessible) to 2D (easier, common in research institutions), in hopes of making this technique accessible to cell biologists.

In this and the previous work, the researchers describe how they combined the two forms of microscopy to achieve the results they were looking for. All forms of microscopy have limitations, especially when it comes to the limits of the optics and sample preparation, and in this case, scientists overcame a barrier between optimizing the available fluorescence and also optimizing the quality of the EM images that were produced.

As you might imagine, the better the overall image quality is, the better biologists can use the image information to help understand the structure and function of biological components, such as organelles and proteins. Additionally, though the cells used in this study were frozen and prepared, there is a possibility that live cells could be directly imaged using this technique.

Though explaining and understanding the method are a little complicated, the pictures make it all worth it—and the scientists would agree. Below are example image sets. The first set is of an image containing mitochondria, or the powerhouse of the cell, and a protein that localizes in its DNA.

The first image in the set shows the result of PALM, the second contains the EM, and the third is the alignment of the two images (and M is for mitochondria).

And here’s a second set, with imaging of a whole cell by traditional confocal microscopy (A), followed by a similar sequence as above (B-D) for a nucleus and the location of a fluorescent dye that adheres to actin (protein) filaments.

The researchers also managed to perform imaging using two colors (title image), demonstrating the versatility of the technique. Check out the full details and image set here, as well as other recent studies involving new imaging techniques here, here, and here.

Citation: Kopek BG, Shtengel G, Grimm JB, Clayton DA, Hess HF (2013) Correlative Photoactivated Localization and Scanning Electron Microscopy. PLoS ONE 8(10): e77209. doi:10.1371/journal.pone.0077209

Image Credits: All images from the article

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Can You Image That? Imaging a Cell and Its Proteins Together