An international team of scientists from the Leibniz Institute for Zoo and Wildlife Research (IZW) in Berlin, Germany, and the University of Sheffield, UK, now answered the question how social status is inherited in one of the most social of all mammals, the spotted hyena. In a study published online last week in the scientific journal Behavioural Ecology, the scientists used observations during the last 20 years of rare cases of adoption among hyenas in the Serengeti and Ngorongoro Crater in Tanzania in combination with the latest molecular techniques to identify genetic mothers to demonstrate that hyena mothers pass on their social status by supporting their young during social interactions with other group members.
In human society and many animal societies, social status is crucial - it determines access to resources, survival and reproductive success. 'In highly developed mammalian societies such as spotted hyenas, social status is even more important to survival and reproductive success than environmental factors, predators or pathogens' says Prof. Heribert Hofer from the IZW. As a result, parents may attempt to pass on their status to their offspring. Such 'rank inheritance' has been observed in a number of mammalian species, including many primates and the spotted hyena.
'In spotted hyenas, surrogate mothers adopt young cubs soon after their birth. The adopted cubs obtained a rank at adulthood that was similar to and just below the rank of their surrogate mother. In contrast, the rank of adopted offspring was unrelated to the rank of their genetic mother' says Dr Marion East from the IZW. 'This is consistent with the idea that maternal behavioural support determines rank inheritance.'
The results of the study are inconsistent with the two alternative hypotheses to explain rank inheritance in social mammals: (i) mothers might transfer genes that cause their offspring to be as competitive as themselves; or (ii) maternal status might determine the concentration of maternal androgens (testosterone) that a foetus is exposed to, and this exposure in turn might make offspring become as competitive as their mother. 'These hypotheses would predict a relationship between the rank of adopted offspring and that of their genetic mother, but we found no evidence of such a relationship' explains Dr Oliver Hoener from the IZW.
The study demonstrates that in spotted hyenas, the young 'learn' during adolescence which group members they can dominate when their mother helps them win contests against group members that are subordinate to the mother. When they become adult, they defend this position and benefit from the 'silver-spoon effect' - because social dominance provides fitness benefits in spotted hyenas, they obtain the benefits associated with this position.