It’s easy to do assume that all animals have a neat dividing line between the sexes, because the differences in appearance between males and females can be very striking. But the more scientists learn about wildlife, the more it becomes clear that nature has no rulebook.
Most people know that male seahorses get pregnant and give birth. However, research reveals more about animals that defy expectations about gender norms.
To understand why some species develop particular traits or appearances, you need to know why the males and females of many species have evolved to look so different from each other. Most of the animal kingdom has a limited number of eggs in females and an infinite number of sperm in males.
This is known as anisogamy and usually results in males competing for females through the evolution of weapons such as antlers on deer or ornaments such as the peacock’s beautiful tail. Consequently, it is interesting that females are more selective about their mating partners.
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 feathers of females has evolved through natural selection, where the strongest survive; in this case those camouflaged from predators.
The bright blue and green feathers of the male maples make them stand out against their background and add to their attractiveness. Females choose the “sexiest” males based on their plumage. Thus, for most species, males are brightly colored and females are dark in appearance.
But this is not always the case. Evolution has created some incredible twists in nature’s story.
6. Wa left-necked Jacobin
A recent study found that about 20 percent of female white-necked jacobins (a species of hummingbird native to Central America) have iridescent blue and green feathers that mimic the coloration of males.
Although females mimic males more in appearance than behavior, they gain the advantage that more aggressive males use. Males avoid females with decorative feathers and leave them alone to make better use of the food.
The narwhal, or sea unicorn, is a long spiral-toothed Arctic whale up to 3 meters long. Males use teeth to attract females and warn off male rivals. The male with the largest female is the most dominant and has the most mating opportunities.
However, a small proportion of females have teeth. The cause is unknown. But if tusks improved 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 one tooth is mostly limited to males, females can benefit as hummingbirds.
4. Bcurled button quail
Some species, such as the hooded button quail (a South Asian ground bird), show a complete role reversal. Females are larger than males and have a black throat and breast patch that males do not have. Females call loudly to attract males and fight for access to their mates.
After the pair mate, the female moves on to her next mate, while the male remains to incubate the eggs and raise the chicks alone. However, this comes at a cost. In the animal kingdom, most females live longer than males, but female button quails live for four years, almost half the lifespan of males.
Women aren’t the only ones who benefit from adopting masculine looks or characteristics. The ruff (a sailing bird from northern Europe and Asia) was named for the collar of feathers that developed around the neck of males during the breeding season, similar to Elizabethan ruffs worn in the 17th century. Men with more impressive ruffs attract more women.
Thus, the best males are spoiled for choice, and some males become lonely hearts with no opportunity to mate at all. But these disgruntled men found a way to beat the players at their own game. Some males copy females during the breeding season, so they can get close enough to females to perform secret matings.
Some ruffs that imitate females will even drive other males away from females. Once the coast is cleared, the false females will return to mating.
Perhaps the most fascinating animal is the spotted hyena of sub-Saharan Africa, whose females dominate clans. They do most of the hunting and raise the young alone. Females are larger than males and have more testosterone, meaning that often the highest-ranking male is subservient to the lowest-ranking female.
Females even have an erect penis with testicles. It is a pseudopenis formed by an enlarged clitoris where females urinate and give birth. The false penis signals dominance when hyenas meet each other, with an erect “penis” acting as a subjugation flag.
1. Asian bighorn hunter
So, in the animal kingdom, looking like a member of the opposite sex has many benefits. Some species of fish, such as the Asian sheepshead wrasse, take this a step further and change sex throughout their lives.
The largest females become males, known as successive hermaphroditism. A change in hormone levels turns their ovaries into testes, allowing them to produce more offspring in their lifetime. We’ve learned a lot 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 Conversation by Louise Gentle at Nottingham Trent University. Read the original article here.