The age of change: social aging in dolphins

Kelley Caroline Meehan, Barbara Class , Shinichi Nakagawa , Vivienne Foroughirad, Janet Mann, Celine Frere

Recent work has unearthed strong relationships between aging and average sociability. Clear patterns of decreases in average sociability are observed across taxa, many of these are sex-specific. Individuals, however, generally deviate from population averages, and discounting individual variance in behaviour could disguise mechanisms of adaptation, selection, and developmental stability. Here, we leverage four decades of behavioural data on a population of Indo-Pacific bottlenose dolphins to bring new perspectives on social aging by exploring individual differences in sociability (repeatability, i.e. personality), its variance (predictability), and how sociability changes (plasticity) and its variance changes (malleability) with age. Novel analytical methods reveal a multidimensional response: individual sociability (group size) changes significantly throughout life, both in average response and underlying variance. Sociability increases for the first two decades of life, then declines with age, a trend more pronounced with males. Predictability of individual sociability, however, increases throughout life, indicating that individual social preferences strengthen (despite oscillations) with age. These patterns suggest that individuals develop social competence, defined as accruing social information via experience, presumably optimising their social relationships for a net fitness benefit. These findings provide novel insights into sex-specific social aging and illustrate how studying variance can reveal processes of competence, selection, and adaptation.