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Dandelions, Darwin’s Bark Spider, and More: No Shortage of Biological Wonders

David Coppedge
Photo credit: John Liu, via Flickr (cropped).

How can Darwinians really enjoy awe and gratitude when believing that everything made itself by chance with no purpose or plan? Well, here is some awesome biology, starting with a commonplace item in the yard — dandelions — that’s featured in a short video from Illustra Media:

Who would have thought that so much engineering expertise is built into a small, lightweight package like that? Now, scientists have found an additional design feature. The two-minute video shows how the pappus closes in moist air and opens fully in dry air, when conditions for flight improve. But it doesn’t explain how. What actuates this response to humidity? 

News from Imperial College London explains how the pappus responds to moisture: “Engineers uncover secret ‘thinking’ behind dandelion’s seed dispersal.”

Their work, published in Nature Communications, found the seed-carrying parachutes open and close, as in the GIF below, using something like actuators — devices that convert signals into movement — without active input of energy. [Emphasis added.]

Animated GIFs show how the actuators work. They use the bilayer principle — as in thermostats — made of tissues that respond differently to moisture. Absorbing humidity from the air, they swell or shrink accordingly. One may be excused for thinking that dandelions are thinking:

Responding to these humidity signals, they ‘decide’ to either open their parachutes and fly away, or to close their parachutes and stay put.

Bilayer differences in moisture absorption properties initiate movement: “differences in capacity to absorb water is key to actuation and therefore parachute opening and closing.” And since these tissues are arranged in a circle, all the parachutes open and close simultaneously. The paper in Nature Communications by Seale et al., “Dandelion pappus morphing is actuated by radially patterned material swelling,” is open access with all the details, including micrographs and movies; fascinating.

Engineers might have to think less about copying this design now that dandelions already “thought” about it — or rather, had thought embedded into their design.

We find that the actuator relies on the radial arrangement of vascular bundles and surrounding tissuesaround a central cavity. This allows heterogeneous swelling in a radially symmetric manner to co-ordinate movements of the hairs attached at the upper flank. This actuator is a derivative of bilayer structures, which is radial and can synchronise the movement of a planar or lateral attachment. The simple, material-based mechanism presents a promising biomimetic potential in robotics and functional materials.

Engineers love self-actuating devices that don’t need batteries. Here was a good one right from the garden. The dandelion seeds can fly for 100 kilometers (62 miles) — much farther than the 10 miles stated in the film.

Darwin’s Bark Spider

The biggest orb webs in the world are spun by Darwin’s bark spider of Madagascar. This spider’s webs, with bridge lines 25 meters long (82 feet) can cross a river! The female, three times larger than the male, lets a silk strand drift into the wind till it catches a branch. Then, the spider crawls to the middle and builds the orb from the top down. The completed web can be almost 3 square meters in size, catching plenty of prey. 

It’s not really Darwin’s spider, because he never saw one. It was only discovered in 2009 but was named for him on the 150th anniversary year of the publication of The Origin of Species.

For such large webs, the silk must be exceptionally strong. And it is: nearly twice as strong as the strongest web silk previously measured. Wikipedia says it is the strongest biological material known, ten times stronger than a similarly sized piece of Kevlar. 

A paper in PLOS ONE by Babb et al. investigated the genome and trascriptome of Darwin’s bark spider, Caerostris darwini. The researchers found 31 putative spidroin genes, including some motifs unique to this species.

Broad expression of spidroins across silk gland types suggests that silks emanating from a given gland represent composite materials to a greater extent than previously appreciated. We hypothesize that the extraordinary toughness of C. darwini major ampullate dragline silk may relate to the unique protein composition of major ampullate spidroins, combined with the relatively high expression of stretchy flagelliform spidroins whose union into a single fiber may be aided by novel motifs and cassettes that act as molecule-binding helices.

Meanwhile, at Shinshu University in Nagano, Japan, researchers are continuing the quest to mimic the properties of spider silk. According to Phys.org, this team went straight to the spiders for their data collection.

In previous studies, experiments were conducted with recombinant spider silk-like proteins instead of natural spider silk. Therefore, the size of the protein was about 1/10 of that of natural spider silk. The research group that includes Dr. Jun Negishi, an expert in biomaterials believed that it is important to collect spider silk directly from live spiders and observe cell adhesion of natural spider silk.

That must have been adventurous lab work.

The researchers prepared three types of spider silk; reeled fibers, film, and nanofiber (non-woven fabric). It was challenging to wind live spider thread so that it would be oriented in the same direction. However, they were able to achieve this and found that there was a difference in the shape of cell adhesion among the three shapes of spider silk.

They published their findings in the journal Langmuir.

Quick Takes

Here are a few other awe-inspiring natural wonders to end on:

Moth scales “act as excellent sound absorbers even when placed on an artificial surface,” reported scientists at the University of Bristol. Photos show the micro-structure of the scales. Because the moth scales are so thin, imitating their acoustical trick could lead to sound absorbing wallpaper and many other applications, especially for the travel industry. Using the lightweight material in cars, trains, and planes could make travel more pleasant while also reducing fuel use and CO2 emissions.

Seals have a secret weapon when hunting in the dark: their movable whiskers. The National Institute of Polar Research reported that northern elephant seals have the most nerve fibers per whisker of any mammal. A research team used video loggers with infrared LEDs to non-invasively monitor the whiskers while the seals foraged in the deep dark ocean trenches (see the movie at the link). “With their whiskers extended forward ahead of their mouth, the seals performed rhythmic whisker movement — protracting and retracting their whiskers — to search for hydrodynamic cues, similar to the ways a terrestrial mammal explores its environment.” This gives the animals precision signals of vibrations in the water from prey. 

Hummingbirds just gave people more reasons to install backyard feeders: they are the most colorful birds in the world. Paul Nelson described hummingbirds as living jewels in the Illustra film Flight. Now Yale University reports that “The range of colors in the plumage of hummingbirds exceeds the color diversity of all other bird species.” Look at the eight sample photos here. The colors, remarkably, are not from pigmented feathers. Rather, it “is the result of nanostructures in their feather barbules, the smallest filaments that project from their feather barbs.” These “structural colors” use diffraction to accentuate and focus certain colors — a trick of physics that delights the female birds and all human birdwatchers.

Wellspring of Wonders

Is that enough awe for one sitting? It’s just a taste. The wellspring of natural wonders never runs dry, because the closer you look, the more evident the design appears. Every part of our world is loaded with examples of functional design with flair.