Relationships can be complicated, especially in the wild. There are dozens of ways for creatures to couple up, whether they’re microscopic bacteria or massive jungle mammals. But as is true for human, there’s no one-size-fits-all in the animal kingdom—and no shortage of variety in reproductive and parental habits.
In the act of furthering their species, male and female animals undertake distinct sex roles. The term doesn’t just refer to their part in copulating, but the specific tasks they fulfill in mating and parenting. A common theme in nature’s courtship world is one female choosing a mate from among competing male suitors, then raising her young, predominantly alone.
Male humpback whales, for example, compete for females and leave calf care to the mother. Other animals, like elephant seals, will form a harem: a group of females led by one male who holds a mating monopoly and interacts little with his offspring. Both scenarios fall under the umbrella of polygyny, where one male mates with several females.
Alternatively in monogamous animals, such as the albatross, a breeding pair mates for life. These are considered conventional sex roles.
However, breeding relationships like matriarchies or female-led harems that fall outside traditional polygyny or monogamy are deemed role reversals.
Role reversals in the sea, sky, and underground highlight the diversity of courtship in the animal kingdom—and the wonderful variety of life on Earth.
In underground colonies of naked mole-rats, a powerful queen reigns over hundreds of blind, hairless subjects. As in bee or ant colonies, naked mole-rat queens are the only females who mate and give birth. She’s joined by one—or occasionally a few—breeding males, who she has granted the right to sire the next generation. The rest of the colony is tasked with baby care, in addition to expanding burrows with their robust teeth and feeding the queen. Biologists call this “extreme cooperative breeding.”
“Naked mole-rats are the most extreme example of this among mammals,” says Melissa Holmes, a behavioral neuroscientist at the University of Toronto. “It’s extremely rare.”
The queen rules supreme by suppressing breeding behaviors in the colony. Researchers suspect she does this with dominant behavior, by pushing and shoving colony members around. When the queen dies, another female may peacefully take her place by starting to mate and bearing offspring. But sometimes, before her death, subordinate females will stage a coup, attacking the queen and fighting to the death for a chance at the throne. Because of their unusually long lifespan–over 30 years–queens can rule for decades if not overthrown.
Above ground in Africa’s floodplains and savannahs, female topi antelopes also take control of breeding situations. Instead of males fighting each other for mates, it’s the female topis who aggressively attack their competitors—some even ambushing couples mid-copulation. The competition is warranted: Female topis are only fertile for one day a year. By mating with around four other males in a day, they increase their odds of conception. Meanwhile, male topis play their own love games, by rejecting females they’ve already mated with and allowing more advances from new prospective mates.
Under the sea
Similar to naked mole-rats, groups of clownfish are also led by one female who is “very much in charge,” says senior aquarist Savannah Dodds at the Oregon Coast Aquarium. Swimming beside her is a male mate, the only fish with permission to fertilize her eggs. Together, they care for their developing eggs until they hatch. But if the female dies, a reversal of a different kind happens: her mate turns into a female and takes her place.
All clownfish are hermaphrodites, meaning they are equipped with both sets of reproductive gear—but they’re all born male. The now-female clownfish begins laying eggs and the largest male in the school assumes the role of fish father.
Sea dragons hiding in the swaying kelp off Australia’s coast take role reversals one step further: the males are the ones who carry and birth babies. Like their seahorse relatives, seadragon males receive unfertilized eggs from females, who leave their young-to-be in a special pocket beneath males’ tails. If a male is unimpressed by a female—who attempts to seduce him with an intricate dance—he rejects the eggs.
But if wooed well, he keeps the eggs and fertilizes them. The eggs develop within their father’s fold for the next six weeks before emerging. Once born, the babies must face the ocean’s dangers and changing currents on their own. Only around five percent of these unique seadragon babies make it, Dodds says, and the International Union for Conservation of Nature considers some species to be near-threatened.
In mainland Australia, male emus also take on dad duty. When breeding season begins, male emus win over females with a slow, neck-waving display. But after mating, instead of incubating the eggs she lays, the mother emu leaves them with her mate and saunters off to repeat the process with someone else—a mating pattern called polyandry. The emu father is left with a clutch of massive eggs and must remain seated in his nest for the next two months. In that time, he’ll forgo food and lose up to one-third of his body weight. After hatching, the dedicated daddy raises his chicks for around a year, teaching them how to survive in the rugged outback.
Meanwhile, in the tropical trees of New Guinea, Australia, and neighboring islands, colorful parrots are challenging the notion that females must be the drab ones in a pair. In a stunning display of reverse sexual dichromatism, where females are more vibrant than males, female eclectus parrots stand out like gems against their nesting hollows with bright red and blue plumage. Their male counterparts sport mostly green feathers, which they rely on to blend into the tree canopy.
Although sex appeal plays a part in the bold palette swap, the females’ coloring likely arose to announce their claim on territory, says Rob Heinsohn, an evolutionary biologist at Australian National University.
“It's a very loud signal of hollow ownership: ‘Don't come here; I will fight you,’” he says.
The hollows that eclectus parrots inhabit are in high demand, and the birds defend them at all costs from other marauding mothers. Their dazzling coloration announces that a tree is occupied, but some females will still kill each other over a prized nest site. Because they guard their hollows around the clock, females rely on their mates to bring them food. And the more mates they have, the more food they get.
Even though they only lay two eggs per clutch, females mate with many males, leading them all to believe they may be the father. The males, chasing the chance to further their lineage, also mate with several females. Males will help to care for all their chicks by bringing fruit from tree to tree, which females eat and regurgitate for their young. This is a type of cooperative breeding called cooperative polyandry, a behavior that combines the parenting methods of the naked mole-rats and the multi-mate habit of emus.
A handful of other birds display reverse color schemes, but “nothing is as bold or obvious as the eclectus parrot,” says Heinsohn. Shimmering in the bright sunlight of the canopy, “there's probably nothing more beautiful in the whole world.”