Scientists from America found that the social status of adult spotted hyenas is inherited completely from the mother and does not depend on how the animals behaved in the process of growing up. However, the lifespan of those individuals who have not been able to maintain his rank in his youth, was lower than their lowborn kin who fight for position in the hierarchy have been better. Article published in the journal Proceedings of the Royal Society B: Biological Sciences.
Life in society has many advantages: cooperation can help you better protect themselves from predators, to protect resources, to produce food. However, in the group of high competition, and competition leads to social stratification and the emergence of hierarchy. Some members of the community are stronger than others, receive more resources and power over them. High social status is closely linked with the biological success of individuals: those who have high standing in the hierarchical pyramid, live longer and reproduce more successfully.
What is to the animal, not only depends on physical strength, but also from less obvious social factors, for example, support for relatives and caring parents. Individuals establish their hierarchical status gradually, as they grow, competing with their peers, playing and winning. In addition, in some societies, social rank is inherited. For example, spotted hyenas (Crocuta crocuta) hierarchical position of the young in 78% of cases corresponds to the status of the mother: a highborn young dominate over their cousins and older brothers and sisters up to 18 months.
It remains an open question how the behavior of young individuals and the maintenance of social rank as the formation affects their biological success in adult life. Scientists from the United States under the leadership of Eli Strauss (Strauss Eli) at the University of Michigan in 1998 watched the social life of spotted hyenas in Kenya’s Masai Mara and evaluated the transformation of their hierarchical status.
The researchers determined the social success of animals using the Elo rating system, which is usually used for calculations of the strength of chess players. After each collision, the young hyenas they were assigned a certain number of points depending on, did they win or lose. The rating depended on how the outcome was predictable: if the individual is hierarchically strong won weak, it received little points. If animal, which one might expect setbacks, managed to win, it has greatly risen in the ranking.
In order to assess the status of the hyenas match the inherited, the authors have developed a “rating deviation Elo”: they considered the difference between mother’s rank and Elo rating, which was calculated on the basis of real social interactions of young individuals. Animals whose behavior is fully consistent with the position of the mother, received a zero deviation of Elo, those who raised their status — positive, and those who dropped — negative.
To determine the biological success used two indicators: life expectancy and number of children (the latter were determined only for females, so as to establish paternity is not always possible).
77.5 percent of the hyenas that have entered adulthood, got exactly the same rank which had their mother at this point, but the deviation of Elo did not affect the hierarchical position of Mature individuals. However, if the younger hyenas did not support inherited status and lost in fights with their peers, their degree of well-being in adulthood varied considerably. Individuals with a negative deviation of Elo died earlier than their more successful counterparts. The same effect was caused by the death of a mother before the cub reached maturity, but the status of the mother does not affect life expectancy.