The peacock spider v. Darwin

A Tiny but Mighty (and Dancing) Example of Design: The Rainbow-Colored Peacock Spider
Evolution News | @DiscoveryCSC

The peacock spider was relatively unknown till Jurgen Otto began photographing them and posting videos of their elaborate, colorful dances. If these spiders were bigger, they would have been a sensation in the animal world long ago. It’s hard to believe such a tiny critter could put on a show like this.

Otto’s YouTube videos get millions of hits. This past September, when five new species were revealed, he told Australia’s ABC News how he became known as Peacockspiderman.

“I took a photograph and then later I went home, looked at it on the computer and was just blown away,” Dr Otto said.

“When I started with all this, there was not a single picture or video of a peacock spider on the Internet.

“Nine years later now, you get many thousand hits when you type ‘peacock spider’ into Google.”

The reaction of people when they see the latest finds remains the same.

“One could think that the novelty of this would all have worn off by now, but people still get excited when they see them,” he said.

We talked about peacock spiders  three years ago, focusing on how much information is packed into their tiny brains. But when it comes to peacock spiders, there’s no such thing as too much. Dr. Otto estimates there are about sixty species and subspecies, all native to Australia. If you only have time for one video, watch “Peacock Spider ‘Stayin’ Alive.’” It features 51 species, showing off their costumes and dance moves put to some familiar disco music (which you can always mute, but don’t).

Peacock spiders are back in the news again, because a new study shows that they have another claim to fame: they are the only animals known that can produce the entire rainbow in structural colors as opposed to pigments. This motivated the researchers to study how they do it, with the expectation that the answer could lead to new technologies.

As with birds and some other animals, it’s the males who are the most colorful and beautiful. Darwinians have their theories about why this is so (e.g., sexual selection), but the number of exceptions to the rule (e.g., in humans) hardly makes it qualify as a law of nature. For our purposes, that’s a side issue. Let’s think about how many ways this spider makes a case for design.

For one thing, as we noted before, there’s a lot of functional design packed into an animal less than 5 millimeters in size! As you watch how fast they move, shaking their legs, wagging their abdomens, and jumping all over the place, think of all the systems required to make that happen. Try packing all this into a 5-millimeter animal with a brain the size of a poppy seed:

Eight eyes and other senses that can find the female, evaluate her readiness to mate, and prepare for the show.

Articulated limbs able to cling to twigs without falling.

Muscles that can twitch faster than Spiderman can fire his web slinger.

Nerves that can activate the muscles, using rapid waves of ions traveling down neurons.

Reproductive organs that are synchronized with the mating dance in both sexes.

Numerous support systems for life, including digestion, circulation, excretion, and more.

Another design consideration concerns how all the higher-order systems sprout from a linear code in the spider’s DNA, and other support codes in its epigenetic systems. As with all multicellular life, the entire higher-order animal develops from a single zygote.

We might further talk about superfluous design. The artistic patterns on the males’ abdomens seem gratuitously beyond anything necessary for mating. Drab animals get by just fine; why the excessive color and beauty? And why the dozens of variations among different species? We could be forgiven for imagining a designing intelligence with an artist’s eye.

Aesthetic considerations, furthermore, lead us to ask why human beings are the only ones who get excited about the mating dances of an unrelated species. Does that speak to human exceptionalism? We don’t see any other animals, except the female spider, watching the performances, but people by the millions are fascinated by these tiny animals that have nothing to do with their own “fitness.” What is the evolutionary explanation for the quality of charm? Of humor? Or enchantment? We don’t eat them or train them to do our work. How did our curiosity, sense of humor, and love for beauty “evolve”?

Already we see that peacock spiders can channel our design intuition in many fascinating directions. And now the news: a study in  Nature Communications with Jurgen Otto as a co-author describes two species of peacock spiders that can produce a whole rainbow spectrum of colors — the only animals known to do so in a mating display. News from the Scripps Institution of Oceanography explains why this is interesting:

Brightly colored Australian peacock spiders (Maratus spp.) captivate even the most arachnophobic viewers with their flamboyant courtship displays featuring diverse and intricate body colorations, patterns, and movements — all packed into miniature bodies measuring less than five millimeters in size for many species. However, these displays are not just pretty to look at. They also inspire new ways for humans to produce color in technology.

Scientists have learned quite a bit about iridescence in butterflies and birds, even in some beetles and tarantulas. Layers of protein crafted into patterns at microscopic scales can interfere with light, intensifying some wavelengths and absorbing others. Deciphering the peacock spider’s optical secrets required an interdisciplinary team of biologists, physicists, and engineers, led by Bor-Kai Hsuing, using cutting-edge imaging technology. Once they had a model and a hypothesis, they used 3D nanoscale printing to test it.

In the end, they found that the intense rainbow iridescence emerged from specialized abdominal scales on the spiders. These scales combine an airfoil-like microscopic 3D contour with nanoscale diffraction grating structures on the surface. It is the interaction between the surface nano-diffraction grating and the microscopic curvature of the scales that enables separation and isolation of light into its component wavelengths at finer angles and smaller distances than are possible with current engineering technologies.

“Who knew that such a small critter would create such an intense iridescence using extremely sophisticated mechanisms that will inspire optical engineers,” said Dimitri Deheyn, Hsuing’s advisor at Scripps Oceanography and a coauthor of the study.

Even so, they only explained the physics, not the aesthetics of how the intricate patterns arise. One team member, faced with high technology in a spider, could not extricate himself from Darwinian thinking:

“As an engineer, what I found fascinating about these spider structural colors is how these long evolved complex structures can still outperform human engineering,” said Radwanul Hasan Siddique, a postdoctoral scholar at Caltech and study coauthor. “Even with high-end fabrication techniques, we could not replicate the exact structures. I wonder how the spiders assemble these fancy structural patterns in the first place!”

The other team members apparently did not need evolution to do their work, because the word does not appear in the paper. The word “design” does, though, some twenty times. Their own engineering designs sprang from the “design principles” of this lowly spider:

[O]ur nano-3D printed prototypes demonstrate that the design principle of the peacock spiders’ scales could inspire novel, miniature light-dispersive components.

By understanding biological design principles and emulating them through engineering, our research may allow light-dispersive components to perform under irradiances, and millimetre length scales, not possible before.

It would be instructive for these researchers if they sat back for a moment and just contemplated the implications of their own words. Or come to think of it, maybe they’ve already done so, but are too prudent and self-protective to go the extra step and spell it out really clearly. So we take the liberty of doing that for them.