Colours, Courtship and Camouflage
When looking around the African savannah, it seems something of a mystery as to how animals evolved the colours that they did. Against hues of yellows and green, you have black and white striped horses, yellow and black spotted cats, and bright crimson and turquoise birds that nest in huge carpets on the ground. Obviously, the ability to hide in plain sight provides a major selective advantage to both prey and predator species. So, wouldn’t it just make much more sense for all animals to have evolved to become simply bland and boring? The evolution of these striking colourations is a scientific conundrum that remains fully unsolved, even today, but they must have evolved for a reason - otherwise, these traits would have disappeared into extinction.
Let us start with the leopard, the yellow and black cat that stalks the green canopies of the forest. Despite this colouration, these big cats have the reputation of being one of the most elusive animals out there and, if you've ever been lucky enough to spot one on safari, you'll have seen how they melt into their background and can disappear in the blink of an eye. Well, it turns out that a leopard's spots are actually a kind of counterintuitive camouflage. This is achieved through a combination of "pattern blending", where the patterns on their body match the dappled lighting of their forested environment, and "disruptive colouration", where their irregular marks break up the body's outline. Together, these phenomena allow leopards to shape-shift through the canopies undetected and help explain why they are one of the most successful of the big cats.
Lions, contrary to leopards, have a relatively straightforward colour pattern, which, by comparison, makes perfect sense to us. But their young are still born with rosettes of light spots, most likely because they are left stashed while the lionesses hunt and the benefits they provide at this time are similar to that of a leopard. As they grow, however, and move out into the savannah, these spots disappear. From that point onwards, lions rely on 'crypsis'. This type of camouflage is characterised when an individual’s overall body colour resembles the general colour of their habitat, like the lion in the savannah. This cryptic colouration allows lions to sneak closer to their prey, before breaking out into a charge and taking them down.
Cheetahs, like leopards, have evolved spots that cover most of their body - this might not come as a surprise to you as they're close relatives, right? Not exactly. While cheetahs and leopards are related, they diverged over 6.7 million years ago. In fact, cheetahs are the only remaining species of the genus Acinonyx, whose closest relative is the puma. Similarly, genets may look like leopards or cheetahs, but their closest relatives are actually mongooses! 'Convergent evolution' occurs when organisms that are not closely related to another independently evolve similar features, since similar behaviours and pressures are driving their survival. Pattern blending and disruptive colouration clearly is the key to success for these animal species.
So, could this explain the colour patterns of the black and white striped horses that dot the African savannah then? Like the leopard, this stark pattern might not seem to blend in with their surroundings, but for a long time, it was assumed that a zebra's stripes, seen on mass as part of a herd, create a 'dazzle effect', optimal illusion, that confuses their predators. This theory was thrown into question, however, by the latest research which claims that while the stripes are for camouflage - it's just not necessarily against predators. Instead, a study published in Nature Communications claims that its stripes are a defence mechanism against annoying biting insects like the horsefly, mosquito and tsetse fly who, for some reason, simply do not seem able to land on striped surfaces!
“What with standing half in the shade and half out of it, and what with the slippery-slidy shadows of the trees falling on them, the Giraffe grew blotchy, and the Zebra grew stripy, and the Eland and the Koodoo grew darker, with little wavy grey lines on their backs like bark on a tree trunk; and so, though you could hear them and smell them, you could very seldom see them, and then only when you knew precisely where to look.” Rudyard Kipling.
The birds of the bush, such as the glorious carmine bee-eater with their turquoise top-hats and trailing carmine tail feathers, or the woodland's kingfisher with their electric blue coats, remain something more of a mystery. Most of the colours that we see occur when pigments, each with a unique chemical structure, absorb certain wavelengths and reflect the complementary one. Other colourations can be down to other optical phenomena, such as refraction, dispersion, or interference. Take the feathers of an open-bill stork for example, who have feathers with a unique structure on their wings which disrupts colour radiation and appear iridescent. It's important to also remember that birds are able to see in a whole other dimension than humans, using ultraviolet rays, and can appear completely different to one another than they do to the naked human eye. Therefore, while a colour might appear counterintuitive to us, it might just work for that species against certain avian predators. On top of that, if a bird nest in somewhere like a tree-hole or tunnel, as opposed to an open location, then there's really no need for them to be bland either.
Interestingly, colours, especially in birds, can change under certain conditions. The most obvious time this happens is when birds are in their most vibrant and lustrous 'breeding plumage' and nowhere are these changes more visible than on heronries. As their hormones rage in advance of the most important time of the year for a sexually receptive bird, chromatophore sizes may swell or shrink, pigments may migrate, and microstructures may reorientate, all changing the appearance of their host. It is the males who tend to develop the boldest breeding plumage, ranging from deep colourations to hilarious feathered plumes that waft in the wind. This sexual dimorphism (difference in appearance between opposite sexes) is thought to arise when sexual selection acts as a driving force in evolution. Partners may choose an individual with vibrant breeding plumage as it may be a subtle indicator that they're a better forager or even because despite sticking out like a sore thumb with their supposedly 'sexy' traits they're still surviving and thriving, and so must have some pretty good genes to pass on.
Our final example is the African wild dog, otherwise known by its Latin name Lycaon pictus, which appropriately translates to the 'painted wolf'. True to this name, wild dogs appear to have been splattered in paint, and each of their coats has a unique mottled print of beiges, browns, and black and white splodges, that is each as unique as a fingerprint. But why did they evolve such unique coats? Possible suggestions include camouflage, most likely as a type of disruptive colouration, thermoregulation, and individual recognition, so dogs can recognise one another and immediately see the place in the pack’s ever-important hierarchy within which they sit. It seems to work for them though as African wild dogs have a success rate at hunts of 80% on average – one of the highest of any mammalian predators.
While camouflage does appear to be the single most important evolutionary force for explaining the overall appearance of animals, there are other selective forces that drive the weird and wonderful colours we see. What is clear is that every animal is unique and different, and has perfectly evolved to fit its niche in its ecosystem. Today, these ecosystems are under threat from all sorts of human interference, whether that be climate change or habitat destruction. As we push animals to the boundaries of their limits, their unique characteristics go from being assets to inconveniences, and there is no telling how they can survive in our new world. It has never been more important that we protect wild spaces and do what we can to limit environmental change for their inhabitants. If you've enjoyed this blog, then please take a moment to think about what you can do to help. Every little truly makes a difference.