Juvenile rank acquisition influences fitness independent of adult rank

Abstract

17Social rank has been identified as a significant determinant of fitness in a variety of 18 species. The importance of social rank suggests that the process by which juveniles come to 19 establish their position in the social hierarchy is a critical component of social development. 20Here, we use the highly predictable process of rank acquisition in spotted hyenas to study the 21 consequences of variation in rank acquisition in early life. In spotted hyenas, rank is 'inherited' 22 through a learning process called 'maternal rank inheritance.' This pattern is highly predictable: 23 ~80% of juveniles acquire the exact rank predicted by the rules of maternal rank inheritance. 24This predictable nature of rank acquisition in these societies allows the process of rank 25 acquisition to be studied independently from the ultimate rank that each juvenile attains. In this 26 study, we use a novel application of the Elo-rating method to calculate each juvenile's deviation 27 from expected pattern of maternal rank inheritance during development. Despite variability in 28 rank acquisition in juveniles, most of these juveniles come to attain the exact rank expected of 29 them according to the rules of maternal rank inheritance. Nevertheless, we find that transient 30 variation in rank acquisition in early life predicts long term fitness consequences for these 31 individuals: juveniles 'underperforming' their expected ranks show reduced survival and lower 32 lifetime reproductive success than better-performing peers. Finally, we present evidence that 33 this variability in rank acquisition in early life represents a source of early life adversity, and that 34 multiple sources of early life adversity have cumulative, but not compounding, effects on fitness. 36risk, cooperative breeding, and cooperative resource defense, are weighed against costs such 40 as increased competition over local resources, pathogen transmission, and risk of social 41 conflict. These costs and benefits may not be experienced by all group members equally; some 42 individuals gain more of the benefits and suffer fewer of the costs than others [1,2]. In many 43 animal societies, this disparity among group-mates is reflected by a dominance hierarchy, 44where individuals differ systematically in their tendency to display subordinate signals to their 45 group-mates [3]. A useful abstraction of the network of complex and unequal relationships 46 among group members is 'rank,' which describes the extent to which an individual is able to 47 exert power over its group-mates. Extensive research from a variety of organisms has 48 demonstrated that individuals of high rank, which are able to exert power over most other 49 individuals in their social group, enjoy dramatic advantages as a result of their position in the 50 social hierarchy, although species vary in the nature and strength of the relationship between 51 social status and fitness [2,4-6]. 52Decades of work has demonstrated various correlates with dominance rank or status 53 within a social group. For ...

The importance of individual‐to‐society feedbacks in animal ecology and evolution

“…For example, populations can become assorted by personality if both personality and social contacts are heritable (Ilany & Akcay, 2016a). Despite its explanatory power, social inheritance and other mechanisms such as genetic inheritance of behavioural traits, remain an underexplored bottom‐up driver of real animal societies and the evolution of other social interactions, such as dominance interactions (but see Strauss, Shizuka, & Holekamp, 2019). Furthermore, little is known about the top‐down consequences of inheriting social contacts in other aspects of an individual animal's life, such as survival and lifetime reproductive success.…”