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Monday, September 20, 2021

Nepotism or social support? Hyena mothers pass their social networks to their cubs

Social inheritance also has a direct impact on the longevity of the mother and the female offspring.

Written by Ritvik Chaturvedi | Bengaluru |
Updated: August 6, 2021 6:20:35 pm
Hyena motherThe paper observes that even though the relationship between a hyena and its mother weakens over time, a higher-ranked individual continued to share a social network similar to that of the mother. (Wikimedia Commons)

Humans are not the only ones who benefit from nepotism. A recent study shows that spotted hyenas (Crocuta crocuta, one of the four extant hyena species) inherit their mother’s social network. This gives them preferential access to resources and reproductive success.

The study uses data from 27 years of continuous field observations of hyenas. It measured the number of times two individuals were observed together. The current study builds upon an earlier pan-species study that established that social inheritance had a direct impact on survival, pathogen transmission, reproductive success and sexual selection. Hyenas, much like baboons or macaques, live in stable matrilineal groups known as clans. Individual ranking within a clan plays a major role in determining the clan structure.

The paper delineates three major pathways through which that happens:

  1. Higher-ranked individuals not only have more time to socialise but also tend to have more potential partners.
  2. Lower-ranked individuals stand to benefit more by trying to form social associations different from that of their mothers.
  3. Offspring of higher-ranked hyenas tend to reinforce their rank by spending most time within the social associations of their mothers.

Strong social network

The authors found that hyena offspring inherited social associations of their mother i.e. social associations of mothers before their cubs left the den was a strong predictor of their cubs’ social network. On the contrary, there was weak evidence to suggest that mothers and offspring formed new social ties, or the mother acquired the offspring’s connections.

The paper observes that even though the relationship between a hyena and its mother weakens over time, a higher-ranked individual continued to share a social network similar to that of the mother. But lower-ranked hyenas were quicker to break free from their mothers’ social network.

Most studies on spotted hyenas have concluded that the rank occupied by an offspring at adulthood is best explained by maternal behavioural support offered by its mother, and that genetic inheritance had little to do with it. For instance, a study on three hyena clans in Tanzania found that the social rank of an offspring bore more similarity to the surrogate mother than the biological mother.

Like mother, like daughter

Social inheritance also has a direct impact on the longevity of the mother and the female offspring (females usually leave the mother’s den later than male offspring). Progenies of alpha females consistently showed far better survival than progenies of lower-ranked females. Social inheritance is also associated with better survival for the mother. It was observed that mothers whose offspring shared much of the social network tended to survive better. This, the authors maintain, might be an indicator of the mother’s good health since hyenas tend to not form ties with the associates of their mother if the latter’s health is in decline.

Clan structure rules The study also attests to the fact that social inheritance plays a major role in stabilising social/clan structure. Copying maternal social preferences in the early years of an individual’s life history, through cultural learning, has been extensively observed for other species as well.

An earlier study that observed 23 captive rhesus macaques in captivity from birth to adulthood concluded that maternal relations significantly determined relations among daughters. Independent studies on the rhesus monkeys have found that a strong mother-child relationship does contribute to a significant kin bias in infants.

A similar study on African elephants (another matrilineal species) also found that social structure was remarkably well-preserved and largely immune to external stressors like habitat destruction and poaching, with older matriarchs continuing to serve as ‘connectivity nodes’.

The author is a freelance science communicator. (mail[at]ritvikc[dot]com)

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