Promiscuous or Faithful? Animals Teach Us a Lesson
Promiscuous or faithful?That is the question. In the animal world, monogamy, polygyny, and even polyandry are all common. On this day, let us introduce you to those monogamous animals.
The Amorous Vole
On the prairies of Illinois in the United States, when spring arrives, youngprairie voles(Microtus ochrogaster) leave their parents and begin to build their own little families. Their "wedding" is both tender and wild: the two voles sniff, lick, and nuzzle each other, groom each other's fur, and will evenmate 15-30 times in a single day. After becoming mates, they stay together, building nests and raising young side by side. However, a female may also bear young fathered by other males, showing that voles are not completely "faithful" animals.Three-quarters of vole couples stay together for life, and if one partner dies, fewer than 20% of voles will accept a second wife or husband.
Although their private lives are very romantic, prairie voles also have a violent side. Within less than a day after mating, a vole will suddenly turn hostile toward "outsiders," and upon encountering any member of its species other than "family," it will pounce and attack.
Frequent mating causes voles to secrete certain hormones, such as oxytocin and vasopressin, which arethe magic potion that manipulates vole love. If we inject a male vole with vasopressin, he will act extremely affectionate toward a female, refusing to take any other, and will fiercely attack other voles. If we use a chemical to block vasopressin from working, the male prairie vole becomes cold and heartless,feeling like he will never love again. And if we inject a female vole with oxytocin, she becomes warm toward a male, as if she will marry no one but him. Strangely, oxytocin does not make female prairie voles violent, so the female's bad temper must have another cause.
A loving pair of prairie voles. Image: pinterest
The fundamental reason the "magic potion" makes voles fall in love still lies in their brains. All mammals can secrete oxytocin and vasopressin, but where in the brain these two hormones take effect varies by species. The prairie vole and its relative the montane vole (Microtus montanus) have different locations in the brain for receiving oxytocin and vasopressin, which makes their behavior strikingly different. The montane vole is utterly clueless about romance;the male runs off immediately after mating, and no matter how much hormone you inject into him, it will not make him fall in love with anyone.
In other words, prairie voles are born "romantics." Among mammals, species that are monogamous like themmake up only about 3%。
Keeping a harem? Can you afford the baby formula?
Monogamy is a puzzle in evolutionary biology. By rights, the more"promiscuous"an animal is, and the more mates it has relations with, the moreoffspring it will leave behind. This is especially true for males, because sperm are much smaller and "cheaper" than eggs; a single male can produce vast numbers of sperm and impregnate many females. Legend has it that Ismail, king of the Moroccan Alaouite dynasty, had more than 500 wives and concubines in his harem and fathered 888 children.
If a "harem" can make an animal's offspring flourish, then why insist on hanging yourself on a single tree? In fact, what we should really ask is:Do you think just anyone can afford to keep a "harem"?？
One male lion with two lionesses; polygyny is not uncommon in the animal kingdom. Image: Uniqornia / weheartit.com
Some animals can gather together in great crowds, while others cannot, and the most important influencing factor here is ecological conditions. For example, when food resources are extremely scarce, if animals gather in a group, they will allstarve to death from lack of food, and a harem becomes out of the question.
Moreover, when even eating is a problem, if you encounter a member of the opposite sex of your species, you will only worry that it will steal your food,and you will not think in naughty directions at all. The reason prairie voles are so amorous may be that they live in resource-poor environments, where each pair of voles holds its own territory and forbids other voles from trespassing. Warmth inward and ferocity outward are, for voles, two sides of the same coin.
Another reason monogamy arises is thatyoung are too hard to raise, and humans surely know this well. Not everyone can afford baby formula for many children the way Ismail could. If your pile of wives and concubines bears a pile of children and they all starve to death, then the "harem" is of no benefit to you. So it is betterto stay faithful to one partner for life, with a couple raising one or a few children together.
In heaven, we wish to be birds flying wing to wing
The most classic example in this regard happens to be birds. "Look up at a hundred birds in flight; large or small, they always fly in pairs";monogamy is extraordinarily common among birds(over 90%). Chicks need a great deal of energy to grow large enough to fly in a short time, so baby birds usually have astonishing appetites. We have all seen mother and father birds darting back and forth through the air in spring, carrying insects to stuff into the chicks' little mouths; this is truly very hard work.Varied tit(Parus varius) chicksmust eat five times per hour, with the parents cooperating to feed them.
Like humans, if a bird "couple" can work together in harmony, family life goes more smoothly. For example, theblack-legged kittiwakes（Rissa tridactyla）"old married couples"that were already together last year lay eggs earlier and raise more chicks than the"newlyweds"that paired up this year. This is because "old married couples"cooperate with greater rapport, and this may be why some birds are reluctant to part with their "first spouse."
A pair of black-legged kittiwakes tending their young on a cliff face. Image: T. Müller / wikipedia
Time is another factor affecting monogamy. If an animal's breeding season is very short, as with certain frogs and seabirds, thepossibility of "having a foot in two boats"drops greatly. Because everyone is "courting" at the same time (a bit like university?), by the time you find one mate, the other members of the opposite sex have long since been"spoken for".
A desire to guard may also lead to monogamy. Like food, a mate is itself a scarce resource. Modern genetic testing technology allows us to do "paternity tests" on wild animals, and the results show that among the offspring of many birds,there are works by "the guy next door". Toiling to feed a chick only to discover it is not your own is simply too terrible. Even more terrible is that many male animals engage ininfanticide: upon finding a female with young, they first kill her young, then mate with the mother.
A male lion commits infanticide, which can prompt the lioness to come into estrus as soon as possible. Image: Paul Joynson Hicks, Barcroft / YouTube
A male animal can watch his mate all day long,not letting a green hat land on his head, but watching a wife takes time and energy, and with many wives he cannot afford the burden, so he often can only keep a close watch on the one in front of him. The small and cutedik-dik(Madoqua spp.) is a rare monogamous antelope; the male dik-dik does not protect the young, but his desire to guard his wife is very strong. He always follows close beside his wife and leaves his scent everywhere, on the one hand to mark territory, and on the other to announce that the female dik-dik is already "spoken for."
Kirk's dik-dik Madoqua kirkii; the upper image shows a female, the lower a male. Image: Yathin S Krishnappa / wikipedia
If you love, stay together for a lifetime
Finally, if the possibility of finding a "other half" is extremely small, thendo not count on "there being plenty of fish in the sea"; the best example of this may be (dioecious) parasites - they cannot walk, have no eyes and not much of a brain, and drift through life inside someone else's body, so "courting and marrying" must be very difficult. So after encountering a mate, they often stay together for life.
Certain species of schistosomes, such asSchistosoma japonicum(Schistosoma japonicum), have mature females and males thatstay stuck together for life. The short, stout male has a groove on his body called the "gynecophoral canal," and he clamps the slender female within it, so that a limbless worm can also (shamelessly) embrace its wife.