What is Biological Ornamentation?

Animals display a wide variety of spectacular accessories. But, what are they and why did they evolve?

The Colour of Love

If you’ve seen any documentary on birds, you’ll definitely have seen a sequence involving the Birds of Paradise. Producers of bird documentaries may fail to include many winged beings in their film, but the one species they will never miss is the Birds of Paradise. Why? Their colourful plumage and brilliant displays of courtship are the answers.

Birds of Paradise, the males, in particular, have exceptionally colourful feathers and tails. They are curious little creatures who decorate their nests with the most eclectic of objects, from shiny pebbles to colourful mushrooms. Their unique courtship dance is an eye-catcher; especially so because it is only the males who indulge in them.

This brings us to the question – what do the females do? Female Birds of Paradise are quite the Plain Jane’s of the bird world. Neither do they have the beautiful plumage their counterparts do nor do they decorate nests or take part in the entertaining courtship ritual.

This isn’t true of only Birds of Paradise. In fact, there are many species where the male does the work and the female remains the spectator. Take peacocks for example. The peacock’s tail is one of the most spectacular in the animal kingdom. Whether roaming in tropical jungles or strutting about in a wildlife reserve, you can always spot a peacock displaying its ‘tail’ing glory with pride.

The peahen, on the other hand, is exceptionally drab. She does not have the magnificent tail feathers that her companion does and she has a more subdued personality. During mating season, you are more likely to spot a peacock strut to a peahen, than the other way around.

When compared to human mating rituals, where males and females play equal roles, the rituals of the animal kingdom leave the work to the men. It is the males which are more colourful than the females and it is the males who have the burden of sealing the deal.

Where Males Strut and Females Observe

In most of the cases (with the exception of lions, zebras, penguins and a few other species) the males fertilize the egg and move on, leaving the female to incubate the eggs and deliver the offspring. If you consider this fact, you’ll notice how the female’s investment in incubation and birth is significantly higher than that of males.

Therefore, once a female is impregnated, chances are she won’t be looking for a new male. The female will lay her eggs or give birth (as the case may be), care for her offspring and once the offspring no longer needs her help, she moves on in search of a new mate.

But, the males, on the other hand, are woven of a different cloth. Males are designed to quite literally “sow their wild oats far and wide”. At the end of the day, the objective of any animal is to continue the existence of its own bloodline. A female, due to her time commitment, will be unable to fulfill this requirement. A male can do wonders here.

Charles Darwin’s Theory of Evolution spoke of two important aspects – sexual selection and biological ornamentation. If a male intends to mate with as many females as possible, the first step is to attract the female’s attention.

Ornamentation serves to attract a number of mates and with it greater chances of mating. Biological ornaments act as indicators of a potential mate’s health and virility, allowing the females to judge whether the male has the genes needed to produce healthy offspring.

Stags with bigger antlers, lions with darker manes, Polyphemus moths with large & hairy antenna and sea slugs with fluorescent colouring are just a few examples of biological ornamentation used in sexual selection.

Weapons of War

Not all biological ornamentation is meant for mating. Some animals take this a step further and turn these ornaments into armaments.

Take orb-weaver spiders for example. These little critters can weave webs of brilliant hues. The rainbow coloured web serves two purposes – a display of virility to the females and an enticing death trap to prey. Bees and other nectar collecting insects mistake these webs for flowers and approach them. Once they land on the webs, it’s almost impossible to escape.

Stag beetles are another example. With one of the largest mandibles of any beetles on earth, stag beetles use these ornaments not just as a weapon of seduction, but also as a weapon of war. When it comes to stag beetles, there is a well-known belief – the larger your mandibles, the more likely you’ll land the female.

Stag beetles reside on trees. When a male sees a female he likes, he climbs up to her with the intention of mating. But, in 9 out of 10 cases, he encounters a rival in his path. In a storybook attempt worthy of being captured in the pages of a classic, the male uses his gigantic ‘antler-like’ mandibles to literally ‘overthrow’ his opponent. The fight for the dark maiden’s mandibles is won only after one male successfully throws his opponent out of the tree.

The Time of the Females

While the males are the recipients of biological ornamentation in most cases, there are certain species where the females are more ornamented or have better armaments.

Take the female seahorse for example. Seahorses are some of the only animals where the male incubates the eggs until hatching. Post-fertilization, the female transfers the eggs to the male and moves on in search of a new mate.

Male seahorses, unlike their other species counterparts, are drab and plain to look at. The females are infinitely more colourful and are much larger than the males. The purpose is obvious. Just like male Birds of Paradise, female seahorses need to look unique and attractive to grab the attention of males. This is a classic case of sexual role reversal in the animal kingdom, with the male preoccupied with rearing the young and the female looking to mate more often.

When it comes to armaments, females can be equally deadly. Take the female angler fish for example. A glowing spine sticking out of the top of her head and large, distended and extremely sharp fang-like jaws, the female anglerfish is gigantic compared to the minuscule male. The spine doubles as a glowing death trap which attracts bioluminescent fish towards her. The male angler doesn’t have any such armaments to boast of.

The female black widow spider is another example. Much larger than the male and extremely poisonous, the females have beautiful hourglass-shaped red markings on their abdomen which are highly attractive to suitors and prey alike; although in most cases, the suitors turn out to be prey themselves.

An Evolutionary Gamble

It all started with a lack of fertile females. With fewer females available to mate with and more competitors than wanted, males had to stand out from the crowd in order to get noticed. As time passed, evolution took its toll.

The change in predatory conditions, problems with weather & pollution, destruction of habitat and the rise & decline in species population numbers all had an impact on the biological ornamentation of animals.

Over the years, some ornaments have remained the same, while others have improved. Some armaments have become vestigial, while others have evolved. The fight for food and mates and the race for survival are the primary reasons for biological ornamentation.

Today, we see so many spectacular ornaments and armaments on display; some of which were non-existent just a handful of years ago. Only time will tell what new biological ornamentation we will get to see in the future.

 

NISHA PRAKASH