In various species of mammals, many offspring are in danger of being killed by a new dominant male in the group who wants to breed his own offspring. This is, in fact, the leading cause of infant mortality among species such as Chacma baboons (Papio ursinus ).
Well, according to a study carried out by zoologists at the University of Cambridge (United Kingdom), the females of some species such as lemurs have developed a strategy to defend their offspring: having as many sexual partners as possible in a short time to confuse the male regarding his paternity.
For the researcher and lead author of the study Dieter Lukas, “when the competition is so intense that a male is not sure of being the father, he avoids infanticide to avoid the risk of killing his own children .” Infanticide – very common among all types of mammals, from mice to primates or lions – is a strategy for males who have little time to secure offspring before another dominant male appears to unseat them.
For its part, the female strategy postpones competition between males after copulation . This has caused their testicles to have evolved to contain as much sperm as possible. Lemur testes, for example, swell 5-10 times more during the breeding season. Lukas suggests that “infanticide by males appears to have influenced the mating behavior of the female. If they copulate with more partners, it is an advantage for them to have bigger testicles, since their sperm will be more likely to beget ”, says Lukas. For example, the Townsend mouse (Microtus townsendii) does not commit infanticides and “has testicles twice as large as some of its close relatives.”
After comparing data from 260 species of mammals, research has revealed that male infanticide occurs in species in which reproduction is monopolized by only a few males. It also supports the idea that infanticide is not a general trait, present in all animals, but is strategic and occurs only when it is advantageous to males. On the other hand, this infanticidal behavior does not modify the female’s preferences for monogamy or other social structure, suggesting that it may not be at the basis of the evolution of mammalian social systems.
“Before it was said that infanticide could be an evolutionary driver in mammalian societies, but it is not. It is a consequence of the variation in sociability, and it is more frequent in species in which both sexes live in stable groups. Infanticide can arise and then disappear: for example, it occurs in chimpanzees but not in bonobos. In the gorillas of the Virunga Mountains (Democratic Republic of the Congo) this practice has ceased to exist. The study also reveals that the greatest challenges facing mammals face throughout their lives do not come from predators or diseases, but from members of the same species ”, concludes Lukas.
