Spiders have rich pigmentary and structural colour palettes

Abstract

Elucidating the mechanisms of colour production in organisms is important for understanding how selection acts upon a variety of behaviours. Spiders provide many spectacular examples of colours used in courtship, predation, defence and thermoregulation, but are thought to lack many types of pigments common in other animals. Ommochromes, bilins and eumelanin have been identified in spiders, but not carotenoids or melanosomes. Here, we combined optical microscopy, refractive index matching, confocal Raman microspectroscopy and electron microscopy to investigate the basis of several types of colourful patches in spiders. We obtained four major results. First, we show that spiders use carotenoids to produce yellow, suggesting that such colours may be used for conditiondependent courtship signalling. Second, we established the Raman signature spectrum for ommochromes, facilitating the identification of ommochromes in a variety of organisms in the future. Third, we describe a potential new pigmentary-structural colour interaction that is unusual because of the use of long wavelength structural colour in combination with a slightly shorter wavelength pigment in the production of red. Finally, we present the first evidence for the presence of melanosomes in arthropods, using both scanning and transmission electron microscopy, overturning the assumption that melanosomes are a synapomorphy of vertebrates. Our research shows that spiders have a much richer colour production palette than previously thought, and this has implications for colour diversification and function in spiders and other arthropods.

Multifunctionality of an arthropod predator’s body coloration

“…This orange coloration is distinct from the yellow colours of crab spider bodies or the spots and stripes in other orb‐web‐building spiders (Blamires et al, ; Chuang, Yang, & Tso, ), and the various shades of red that occasionally appear (e.g. Blamires et al, ), so is likely derived from different pigments (Hsuing et al, ). Some individuals have additional red spots on their book lungs (see Figure a).…”

“…The variety in body colour patterns among spiders is thought to be primarily a product of body surface features so most are unlikely to be readily changed (Hsiung, Deheyn, et al, ). However, recent analyses have implicated cuticular pigments such as carotenoids, ommochromes, bilins, guanines and eumelanins as producing vibrant spider body colours that are changeable across habitats or diet (Hsuing, Blackledge, & Shawkey, ; Hsuing, Justyn, Blackledge, & Shawkey, ; Insausti & Casas, ).…”

“…The function of different body colours, for example yellow, white, green, silver and so on, within spider species has been examined in detail (Blamires et al, , ; Tso, Liao, Huang, & Yang, ; Tso et al, ), but bright orange is a relatively rare body colour in spiders. This may be because orange body coloration is a product of cuticle β‐carotenoid deposition (Toews, Hofmeister, & Taylor, ), and few spiders produce cuticular carotenoids de novo or are unable to attain them from their diet (Hsuing et al, ). We have incidentally noticed that H. multipuncta positions itself in a manner that displays its dorsal orange bands when foraging and lifts its abdomen to expose its bright orange ventrum when disturbed.…”

High contrast yellow mosaic patterns are prey attractants for orb‐weaving spiders

“…They are sit‐and‐wait foragers that rely on a range of strategies to acquire prey. These strategies include modifying the architecture of the web in response to fluctuating prey availability (Blamires, ; Blamires, Martens, & Kasumovic, ; Blamires & Tso, ; Heiling & Herberstein, ; Sandoval, ; Schneider & Vollrath, ), and exploiting different sensory channels to attract prey to the vicinity of the web, for instance by adding odours (Henneken, Goodger, Jones, & Elgar, ), colours (Craig, Weber, & Bernard, ; Hsiung, Justyn, Blackledge, & Shawkey, ), silken decorations (Tan et al, ; Walter & Elgar, ; Yeh, Blamires, Liao, & Tso, ) or prey remains (Bjorkman‐Chiswell et al, ; Tan & Li, ) to their webs, as well as conspicuous colour patterns on the body (Peng, Blamires, Agnarsson, Lin, & Tso, ; Tso, Lin, & Yang, ). There is remarkable variation in the colour patterns of web‐building spiders, and the commonly seen yellow or orange mosaic pattern on the ventral surface of orb‐weaver spiders can serve as visual lures to enhance foraging success (Blamires et al, ; Chuang, Yang, & Tso, ; Liao, Liao, Blamires, & Tso, ; Tso, Liao, & Huang, ; Tso, Tai, Ku, Kuo, & Yang, ; see also White & Kemp, for a review).…”

Unique evolution of vitamin A as an external pigment in tropical starlings

“…Carotenoids, melanins and porphyrins derive from the metabolism of three chemical precursors: mevalonic, shikimic and levulinic acids, respectively (Gudin, 2003). Other exclusive classes of pigments are only found in particular groups of animals, such as psittacofulvins in psittaciform birds (parrots and allies;Martínez, 2009), spheniscins in penguins (Thomas et al, 2013) and ommochromes in spiders and other invertebrates (Hsiung et al, 2017).…”