Scientists have uncovered the secret behind the dominance of female hyenas
Why is it that in some families success is passed down from generation to generation, whilst in others it is not? Scientists have unexpectedly found the answer to this question in spotted hyenas. It turns out that the authority of alpha females does not end with their own lives: their high status is inherited by their daughters, then their granddaughters and great-granddaughters, thanks to which their line gradually begins to dominate the entire clan.
A new study has shown that it is precisely the inheritance of social status through the maternal line that explains why, among hyenas, females are more successful than males at passing on their genes to future generations. The study has been published in the journal *Science Advances*.
Almost 30 years of observations
The study is one of the most extensive in the history of research into spotted hyenas.
Biologists analysed data on more than 2,700 animals representing eight generations and eight clans, which were monitored over a period of 29 years in the Ngorongoro Crater in Tanzania.
The main aim was to determine who, in the long term, leaves behind more offspring — males or females.
The initial findings surprised the scientists
If we consider only the number of offspring born, spotted hyenas are no different from most mammals.
As expected according to classical evolutionary theory, the differences between males turned out to be greater: some produce significantly more offspring than others.
However, everything changed when the researchers tracked not only the offspring, but also the grandchildren, great-grandchildren and subsequent generations.
It was then that it became clear that the advantage was gradually shifting towards the females.
Alpha females create veritable dynasties
The reason turned out to lie in the structure of hyena society.
Each clan lives according to a strict hierarchy, headed by an alpha female.
High status brings numerous advantages:
- priority access to food;
- faster growth of cubs;
- better survival rates for offspring;
- an earlier start to reproduction;
- more offspring over a lifetime.
Most importantly, daughters inherit their mother’s status.
Therefore, these advantages do not disappear after the death of a single female, but continue to be passed on to subsequent generations.
After a few generations, almost the entire clan consists of descendants of the alpha line
The authors provide illustrative statistics.
In a single generation, around 10 per cent of all offspring are direct descendants of alpha females.
By the very next generation, around 20 per cent of the clan’s members have an alpha grandmother.
And after six generations, virtually all the hyenas in the clan turn out to be descendants of a few dominant maternal lines.
In this way, social advantage gradually accumulates, evolving into a veritable family dynasty.
Why males cannot do the same
High status also helps young males, but only temporarily.
When the time comes to breed, males almost always leave their home clan and join another.
In doing so, they lose their high status and can no longer pass on to their offspring the advantages gained through their mother.
Females, on the other hand, remain in their natal clan and retain their rank throughout their lives.
This is precisely why the influence of the maternal line grows stronger with each generation.
Why this is changing scientists’ views
For a long time, it was thought that males of most mammals competed more fiercely than females, which is why the greatest inequality in the number of offspring is observed among them.
New research shows that this conclusion may depend on how far back into the family history researchers look.
If only offspring are taken into account, the picture is consistent with classical theory.
But if several generations are traced, it turns out that in the case of spotted hyenas, it is the females who emerge as the main winners in the evolutionary race.
According to the authors, a similar mechanism may exist in other animals where social status is also passed down through the maternal line.
Why this is important
The study shows that it is not only genes that can be inherited, but also social advantages, which have a huge impact on a family’s evolutionary success.
The study also helps to explain why, in some species, it is the females who become the main focus of competition, despite the fact that in most mammals the situation is the opposite.
Going forward, the researchers plan to investigate whether a similar mechanism operates in meerkats, seahorses and other animals with unusual social organisations.
Source
Journal: Science Advances.
Study title: The legacy of privilege: Social inheritance reverses sex differences in reproductive inequality in the spotted hyena.