Peacock spider’s radiant rump comes from teeny tiny structures

Pigments produce reds and creamy yellows, while nanostructures turns other parts blue
Oct 26, 2016 — 7:00 am EST
peacock spider

The peacock spider gets its blue bling from small reflective structures.

JÜRGEN C. OTTO (FLICKRYOUTUBE)

Male peacock spiders know how to work their angles and find their light. These arachnids are native to Australia. And males are quite a sight to see. They rely on the vibrant hues coloring their hind ends to attract females. A guy will raise skyward  his derriere — or, more accurately, a flap on his hind end — and shake it catch the gals’ attention. Now scientists have figured out where his fancy colors come from.

Doekele Stavenga is an expert in optics at the University of Groningen in the Netherlands. He and his colleagues started by collecting peacock spiders. They found these specimens of Maratus splendens in a park outside Sydney, Australia. Then they zoomed in on the scales that cover the spiders’ rears.

The team used microscopy, spectrometry and other techniques to image the scales. The red, yellow and cream scales rely on two pigments to reflect their colors. (Pigments are chemicals that reflect light to produce colors.) Even the white scales contained low levels of pigment. Spines lining these scales scatter light randomly. That gives them slightly different hues when viewed from different angles.

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spider structures
Scientists made close-up images of a peacock spider’s rear end with a scanning electron microscope. The results reveal the miniature scales that produce colors in the hairlike scales that adorn the spider: white (left), red or yellow (middle) and blue (right; whole structure at right, detail at left).
D.G. STAVENGA ET AL/J. R. SOC. INTERFACE 2016

Blue scales worked differently. They’re transparent and lack pigment. Instead, the shape of the scales cause them to reflect iridescent blue and purple hues. Each scale resembles a sac or a peapod. It is lined with tiny ridges on the outside. Inside there’s a layer of threadlike fibers. The spacing of those fibers may determine whether scales appear more blue or more purple.

Whether peacock spiders’ eyes can actually see these posterior patterns is not certain, the researchers say. Species of jumping spiders can see at least three color ranges, just as humans do. So it seems unlikely that such vivid, come-hither dance moves play out in only black and white.

The findings appear in the August Journal of the Royal Society Interface.

A male peacock spider’s rear end is adorned with bright colors. After waving at a gal to get her attention, he uses his eye-catching decoration in a shimmy-like dance. It's designed to further rev up the interest of a female, which in his species is drably colored.
Peacockspiderman (JÜRGEN C. OTTO)

Power Words

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angle     The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.

arachnid     A group of invertebrate animals that includes spiders, scorpions, mites and ticks. Many have silk or poison glands.

chemical     A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.

colleague     Someone who works with another; a co-worker or team member.

fiber     Something whose shape resembles a thread or filament of some kind. (in nutrition) Components of many fibrous plant-based foods. These so-called non-digestible fiber tends to come from cellulose, lignin, and pectin — all plant constituents that resist breakdown by the body’s digestive enzymes.

iridescent     Adjective that describes something that seems to change color with a shift in the angle at which it is viewed or at which lighting is applied.

native     Associated with a particular location; native plants and animals have been found in a particular location since recorded history began. These species also tend to have developed within a region, occurring there naturally (not because they were planted or moved there by people). Most are particularly well adapted to their environment.

optics     Having to do with vision or what can be seen.

organism     Any living thing, from elephants and plants to bacteria and other types of single-celled life.

pigment     A material, like the natural colorings in skin, that alter the light reflected off of an object or transmitted through it. The overall color of a pigment typically depends on which wavelengths of visible light it absorbs and which ones it reflects. For example, a red pigment tends to reflect red wavelengths of light very well and typically absorbs other colors. Pigment also is the term for chemicals that manufacturers use to tint paint.

range     The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists. (in math or for measurements) The extent to which variation in values is possible. Also, the distance within which something can be reached or perceived.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

spectrometry      The collection of data using an instrument that measures a spectrum, such as light, energy or atomic mass. Typically, chemists use this technique to measure and report the wavelengths of light that it observes to help identify the elements or molecules present in an unknown sample.

spider     A type of arthropod with four pairs of legs that usually spin threads of silk that they can use to create webs or other structures.

transparent     Allowing light to pass through so that objects behind can be distinctly seen.

Citation

Journal:​ ​D. Stravenga, J. Otto and B. Wilts. Splendid coloration of the peacock spider Maratus splendensJournal of the Royal Society Interface. Vol. 13, August 2016. doi: 10.1098/rsif.2016.0437.

Journal: D. Zurek et al. Spectral filtering enables trichromatic vision in colorful jumping spidersCurrent Biology. Vol. 25, May 18, 2015, p. R403. doi: 10.1016/j.cub.2015.03.033.