Bloody hunts, territorial disputes, coprophagy: the animal world doesn’t seem very romantic. When it comes to reproduction, we usually think of protocol copulations and brief unions – here and now, there is no future. There doesn’t seem to be what gives the heart and makes the lovebirds stay together forever. But the truth is that monogamy is not exclusive to humans.
Gray wolves, swans, macaws, penguins – what do these animals have in common? Second Renato Ordones, a veterinarian who works with wild animals, they are some examples of monogamous species, that is, that spend their entire lives with only one partner. “The white-headed eagle, for example, migrates in a solitary way, but usually returns to the same partner during mating seasons”, says the professional.
There are also studies citing monogamy in shrimp, crabs, sharks, cichlids, beavers, marsupials, monkeys, among others.
The two of us, one by one
An article written by Charlotte Kvarnemo, professor of zoology at the University of Gothenburg (Sweden), makes it clear that monogamy can occur unilaterally in the relationship. This is what happens to a species of fish called Ceratias holboelliwhose males, significantly smaller than females, remain monogamous, while their mates may practice polygamy.
Among seahorses, both sexes benefit from monogamy, which usually yields larger litters.
Who is to say that there is no reason?
Second Rafaela Rodrigues Almeida Ribeiro, a veterinarian who works with an emphasis on medicine for wild animals and unconventional pets, genetics is a factor that can explain monogamy in animals. “Species with reduced ecological niches have a greater potential to be evolutionarily monogamous, as they have some difficulty in finding a compatible partner”, she explains.
Charlotta’s article points to habitat limitation as an important reason for monogamous relationships between marine mammals, birds and fish. This reduces potential mates, and in some cases it can be more advantageous to stick to one mate.
For butterflies, time is what ends up limiting the number of partners. Because they live very little during adulthood and have long copulations, these animals tend to have a single pair throughout their lives.
The male’s difficulty in caring for many females at the same time may also explain why some of them mate exclusively with a particular mate.
Another important element seems to be reproductive success. For example, in seahorses, already mentioned, this practice usually generates more offspring, which is beneficial for the perpetuation of the species.
Male spiders, in turn, have two pedipalps, structures that, among other functions, serve for copulation. Each pedipalp can only be used once, so the male has two options: fertilize two different females or practice monogamy, fertilizing a single spider with twice as many sperm, which increases the chances of success.
There are even some species of monogamous birds that “divorce”, that is, find a new partner, when they fail to reproduce.
In addition, it is worth remembering that monogamy can occur both spontaneously and forcefully. In the latter case, one of the parties strives to “protect” the other from possible “suitors”, and may even become aggressive and kill rivals, as happens with house sparrows.
Inside I devour you
In certain species, females can force males into monogamy to avoid sharing resources. This is why the female praying mantis, for example, devours the male after copulation. This practice is called sexual cannibalism.
But they are not the only ones who do everything to be unique. Some male insects inject substances into the female after copulation to prevent her from having other mates.