It’s easy to Assume that all animals have a neat dividing line between the sexes, because the differences in appearance between males and females can be so striking. But the more scientists learn about wildlife, the clearer it is that nature has no rule book.
Most people know that male seahorses get pregnant and give birth. However, research reveals more about animals that defy expectations about sexual norms.
To understand why certain species evolved particular traits or appearances, you need to know why males and females of many species evolved to look so different from each other. Throughout most of the animal kingdom, females have a finite number of eggs, while males have an infinite number of sperm.
This is known as anisogamy and usually causes males to compete for females through the evolution of weapons, such as antlers on deer, or ornaments, such as the peacock’s beautiful tail. Consequently, it is in the interest of females to be more selective about their mates.
These differences in the appearance of the sexes evolved through a process called sexual selection.
A good example of this is the mallard, one of the most common ducks in the world. The brown color of the female’s feathers evolved through natural selection, where the fittest survive. in this case, those camouflaged by predators.
The bright blue and green feathers of male mallards make them stand out against their background, but also add to their attractiveness. Females choose the “sexiest” males based on their plumage. Thus, for most species, males are brightly colored and females have a somber appearance.
But this is not always the case. Evolution has created some incredible twists in the history of nature.
6. Wcollared Jacobean
A recent study found that about 20 percent of female white-throated jacobs (a species of hummingbird from Central America) have iridescent blue and green plumage that mimics the coloration of males.
Although females mimic males only in appearance rather than behavior, they gain the advantage enjoyed by more aggressive males. Males avoid females with decorative plumage, leaving them alone to have better access to food.
The narwhal, or unicorn of the sea, is an arctic whale with a long spiral tusk, up to 3 meters long. Males use the tusk to attract females and warn off male rivals. The male with the largest tusk is the most dominant and has the most mating opportunities.
However, a small percentage of females have tusks. It is not known why. But if tusks increase the chances of survival (by fighting off predators or spearing food), they would have evolved through natural selection in both male and female narwhals. Since the presence of a tusk is largely restricted to males, tusk females may benefit similarly to hummingbirds.
4. sibuttoned quail
Some species, such as the button quail (a South Asian bird), exhibit complete role reversal. Females are larger than males and have a black neck and chest patch that males lack. Females make a loud call to attract males and fight for access to mates.
Once a pair has mated, the female moves on to her next mate, while the male is left to incubate the eggs and raise the chicks on his own. However, this comes at a cost. In the animal kingdom, most females have a longer life expectancy than males, but female quail have a lifespan of four years, almost half the lifespan of males.
It’s not just females who benefit from adopting male looks or characteristics. The ruff (a bird from northern Europe and Asia) takes its name from the collar of feathers that grow around the neck of males during the breeding season, similar to the Elizabethan ruffs worn in the 17th century. Males with more impressive frills attract more females.
Thus, the males with the best swells are spoiled for choice, while some males end up as lonely hearts with no chance of mating. But these disgruntled males have found a way to beat players at their own game. Some males copy females during the breeding season so they can get close enough to the females to do some sneaky mating.
Some of the ruffs played by the females will even lure other males away from the females. The pseudo-females will then return to mate once the coast is clear.
Perhaps the most fascinating animal is the spotted hyena of sub-Saharan Africa, where females dominate the tribes. They do most of the hunting and raise the young by themselves. Females are larger than males and have more testosterone, which means that often the highest-ranking male is subordinate to the lowest-ranking female.
Females even have a penis, filled with testicles, capable of erection. This is a pseudopenia, formed by an enlarged clitoris through which females urinate and give birth. The false penis signals dominance when hyenas encounter each other, with an erect “penis” acting as a flag of submission.
1. Asian sheepshead wrasse
So in the animal kingdom, there are many benefits to looking like a member of the opposite sex. Some species of fish, such as the Asian sheephead, take it a step further and change sex during their lifetime.
Known as successive hermaphroditism, older females turn into males. A change in hormone levels causes their ovaries to transform into testes, allowing them to produce more offspring in their lifetime. We’ve learned so much about the animal kingdom since the dawn of modern science, but as these new studies show, we may have only scratched the surface.
This article was originally published on The conversation with Louise Gentle at Nottingham Trent University. Read the original article here.