Animals, the mating strategies you don’t expect

Let’s put aside gender issues, because in the animal kingdom it is really difficult to define rules and conventions. Monogamists can be counted on the fingers of one hand, pretending to be the other sex is a strategy for mating and there are also real sex changes during life. All this, to ensure a longer survival to the species and a happier and more serene existence for individuals. Seven emblematic examples of these behaviors and role reversals are reported in an article published in The Conversation. They are, to all intents and purposes, reproductive strategies that each species, on the basis of its own characteristics and the social rules in which it lives, implements. How? We talked about it Giuseppe Boglianiprofessor of zoology at the University of Pavia, with an eye on illustrious examples living in our country.

The strategies to get noticed. Or not

All the reproductive strategies implemented by the various species concern the sexual reproduction, the one in which each of the two parents contributes to the offspring with half of their genetic patrimony. The first advantage of this type of reproduction is theincrease in genetic diversitywhich makes the offspring more equipped to cope with any changes in environmental conditions and more resistant to pathogens.

In most of the animal kingdom, females have a finite number of eggs, while males produce an almost infinite number of sperm. This phenomenon is known as anisogamy and is the main reason males compete for females by developing a variety of physical adornments and weapons, such as deer antlers or peacock tail. This rule, however, does not always apply and in general it can be said that the sex that takes care of the offspring is less conspicuous.

“It’s a consequence of predation, which usually acts on the individuals who take care of the offspring “, explains Bogliani.” In birds, whoever takes care of hatching, the more it looks like a dry leaf, the better. If the role belongs to females, then, males have every interest in being colored, partly to be seen by females, partly to impose themselves on other males. In the case of the color of the plumage, the strategy implemented also attracts the predators more, but allows them to have greater reproductive success and to be chosen, perhaps, by more females “.

Feathers, antlers and songs

Let’s take the Mallard. The blue and green feathers of the males make them noticeable to the environment, and also increase their attractiveness. And females choose the sexiest males based on their plumage. Thus, for most species, the males are brightly colored and the females have a sombre appearance. And, if in the case of birds it is a question of ornamentation and color, in the deer this is noticeable in the large antlers and in the frogs in their song.

“Until a few years ago it was thought that the only possible strategy for males, to ensure the transfer of their genetic heritage to their offspring, was to get noticed”, continues Bogliani. “Indeed, some research on IBEX carried out a few years ago in the Gran Paradiso park, and aimed especially at studying the adaptive value of behaviorshave shown that this is not the case. “

These studies measured the reproductive success true, by reconstructing the parental link between individuals (who is the child of whom), and they found that adult males with heavier horns were not always successful. There were males of four or five years, with half the size of horns who, secretly, managed to impregnate a female.

“Their strategy was the other way around. In practice, while two adults fought over their partners and argued with each other to determine who had the right to mate, the smaller boy – who also looks a bit like the female because he has insignificant horns – succeeded. to sneak in and mate first. And the success of this strategy is remarkable, because a significant fraction of the Alpine ibex calves are born from these matings. “

Another local example of this behavior is that of the black redstart, a little bird that nests in the Euganean hills. The male is black, shiny and with a brick-colored tail, he can sing and implement all the best strategies to attract the attention of the female, who instead has a grayish color a little dull. Also in this case, some males, mostly young and who have not yet assumed the same plumage characteristics of the adults, approach the females without being noticed by the other males (who do not recognize them because they resemble females), and couple.

Less conspicuous who takes care of the offspring

The sex that takes care of the offspring is less conspicuous, we said. In the sea ​​horses, for example, the situation is the other way around: the female lays her eggs in the belly of the male, which fertilizes them, while the female moves away. Even in fish it is very common for males to carry out parental care. Males build nests to attract females through dances, and to make them lay eggs. The male then fertilizes and assists them.

“The rule is that the last one with the children is the one who has to look after them, and therefore guarantee the reproductive process”, explains Bogliani. And, when it is the male who has to take care of the offspring, it is often the females who have to work to get noticed. “L’reversal of roles it exists in many European species. One of these is the tortolino plover, in which the females are all colored and the males are gray, the opposite of the mallard, therefore, because it will be the male to look after the eggs while the female will continue elsewhere to lay new eggs. Even in cases where there is this reversal of roles, however, the females pay a significant cost in reproduction because they have to produce eggs, which are voluminous, contain a lot of energetic material and calcium “.

Sometimes monogamy wins

The fact that females almost always pay the higher cost, because they produce larger and more “expensive” eggs and gametes for the organism, therefore, means that it costs less for males to bear more children. “Unless it is essential in paternal contribution to implement parental care, and in that case there are situations of temporary monogamy or that it can last a lifetime “.

Examples of this situation are found in many passerines, who are socially monogamous because male parental care is indispensable. The roles are almost always quite separate, in the sense that the male takes care of the territorial defense, of the feeding of the female during the reproduction of the eggs and of the hatching, and then both take care of the nourishment of the young.

“In some species, the male contribution to the offspring is essential to ensure the success of reproduction terns, seabirds that to get the fish dive from a good height, to catch them one at a time. A female who is about to spawn and already has the egg formed inside, is at great risk if she dives into the water like that. The fact that the male feeds her during this period therefore has an undoubted practical advantage “, concludes Bogliani.