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IMA > News  > Colourful Connections: Unravelling the Threads of Significance in Nature’s Diverse Palette

Colourful Connections: Unravelling the Threads of Significance in Nature’s Diverse Palette

Crayons are some of the first writing instruments we are given as children as we learn about the world around us. I’m sure everyone can remember their first pack as they sat in their desks at primary school. Every basic set would have red, green, blue, orange, yellow purple, with some fancy shades thrown in between depending on the extent of your crayon collection. Colours were some of the earliest ways in which we learned about the world around us, drawing first a factually incorrect yellow sun, inaccurate birds, green stick trees, and scribbles that served as ocean waves. Nature regales us with its colourful palette each day and serves as the inspiration for many  artists;, amateur or professional. 

Nudibraunch

Have you ever wondered though, why there are so many colourful living things around us? Why isn’t the world colourless?  Do colours exist simply for our amusement? To be drawn by unsuspecting infants and toddlers on a messy scrap book? Or to be the muse of legendary artists like van Gogh? Or is there some bigger purpose to the resplendent plumage of a peacock or the vivid colours of reef fish?

Research suggests that there are two broad functions of this spectrum of colours:  they prevent some organisms from being eaten or they help them attract a mate. Seems simple enough. Don’t get eaten and procreate, the essence to most of life. Bright colourations are a call for attention in the animal kingdom, “Look at me, I am nice to mate with!”  –  the social media influencers of nature, or “you better don’t eat me, or this will end badly for you!” – nature’s warning label. 

In each case, the animal is trying to convey a message, but before we get into that, where do these bright colours come from? It is actually a lot more interesting than you realise. Two strategies are employed when mother Gaia decides to set up her easel and canvas and start painting:  pigmentation, the incorporation of nanostructures, or both. Pigments, for example those in skin, absorb some wavelengths of light and reflect others thereby producing a specific colour. Nanostructures on the other hand can amplify the reflections of certain wavelengths of light creating colours such as those found on iridescent butterfly wings. These nanocrystals enable chameleons or octopuses to change their skin colour thank to chromatophores (cells that produce colour) that lie beneath their skin layer. 

So back to the original point, why go through all this trouble of emitting and reflecting light through these different processes? One of my favourite marine creature provides an answer; the beautiful sea slug or nudibranchs that might be equally at home amongst the colourful displays during Carnival as it is in the bottom of the ocean,. Nudibranchs are certainly not shy as their flamboyant displays are unmissable. They are the very embodiment of the saying, “you are what you eat”. Through their diet of sponges, tunicates, hydroids and jellyfish, nudibranchs ingest the toxic chemicals present in the stinging cells (nematocysts) of these organisms, giving them stinging capabilities of their own. Through a process called aposematism (from the Greek words “apo” for away and “sema” for sign), the bright body colourings of nudibranchs signal to their predators that eating them is dangerous. 

There are, however, some pretenders. While some organisms are genuinely aposematic, others simply pretend they are. This is called Batesian mimicry. As anyone who has ever worked on a group project knows, there are some who are comfortable taking the credit while others do the hard work. This is known as a mimetic relationship, one where one organism benefits from looking like another. So in essence, these pretenders don’t actually do the work of producing poison but they simply look like they do. Bright colours are nature’s caution tape, so some organisms benefit from just putting up the caution tape without the actual caution. Most fishes found in coral reefs fall into this category of Batesian mimics. 

Examples of these mimics include the pinnate batfish (Platax pinnatus) which is brightly coloured like a flatworm and even swims like a flatworm by undulating its fins like they do. Why does it do this? As anyone who dines in Poseidon’s kitchen knows, flatworms hardly make a good entrée, so looking like one makes any fish less likely to end up as another predator’s dinner. The general distaste for sea slugs also makes them great muses for mimicry. The bridled burrfish, Chilomycterus antennatus mimics the looks of the spotted sea hare (Aplysia dactylomela) during its larval stages which enables them to have a greater chance of survival to grow onto maturity. Both of these are found in the beds of turtle grass (Thalassia testudinum)

Lots of other examples of fish mimicry exist such as the relationship between fang blennies (Meiacanthus spp.) and mimic blennies, (Ecsenius graviera) but mimicry is not the only survival technique that explains body colourations. Another such technique is countershading or Thayer’s Law.  Usually, the top of an animal’s body is darker compared with the underside of it, with some notable exceptions such as the Luna caterpillar (Actias luna) where the reverse is true. The difference between light and shading is a powerful visual cue, one long exploited by legendary artists like Leonardo da Vinci in a process called sfumato, where a three-dimensional representation of a figure can be perceived on a two-dimensional canvas or piece of paper. This is created by using darker colours or shading for the underside of a structure. Yet another example of art’s interplay with nature. 

This makes countershading important as a form of camouflage. For instance, viewing a shark from above, the ocean gets darker when looking downwards, so the grey colour of a shark’s skin would blend in more easily with this colour scheme. However, viewing a shark from below where there is more light above, the white under belly would offer a better degree of camouflage. This type of camouflage would be useful to enable predators to be undetected when hunting for prey. It is also true for prey who are trying to blend in to their background to make it harder for predators to detect. 

Yellows, blues, greens and all other colours that exist in nature’s diverse palette do not simply exist for our viewing pleasure but they are essential to the survival of nature itself as I have tried to demonstrate. Of course, the colours are greatly appreciated and this is probably one of the reasons why it is recommended to take a walk-in nature to improve your mood and your mental health. So next time you glance out of your window and marvel at the vibrance of a saffron finch (Sicalis flaveola), or take a swim in the ocean and interact with a nudibranch, keep in mind that there is more to those colours than simple aesthetics.

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