Social life histories: jackdaw dominance increases with age, terminally declines and shortens lifespan

Abstract

Behaviour may contribute to changes in fitness prospects with age, for example through effects of age-dependent social dominance on resource access. Older individuals often have higher dominance rank, which may reflect a longer lifespan of dominants and/or an increase in social dominance with age. In the latter case, increasing dominance could mitigate physiological senescence. We studied the social careers of free-living jackdaws over a 12 year period, and found that: (i) larger males attained higher ranks, (ii) social rank increased with age within individuals, and (iii) high-ranked individuals had shorter lifespan suggesting that maintaining or achieving high rank and associated benefits comes at a cost. Lastly, (iv) social rank declined substantially in the last year an individual was observed in the colony, and through its effect on resource access this may accelerate senescence. We suggest that behaviour affecting the ability to secure resources is integral to the senescence process via resource effects on somatic state, where behaviour may include not only social dominance, but also learning, memory, perception and (sexual) signalling. Studying behavioural effects on senescence via somatic state may be most effective in the wild, where there is competition for resources, which is usually avoided in laboratory conditions.

Experimentally increased brood size accelerates actuarial senescence and increases subsequent reproductive effort in a wild bird population

“…For nestling survival, in contrast, there was a quadratic effect of time in treatment and the shape of these curves differed between treatments with a remarkable decrease in nestling survival of the RE− group over the first 3 years of treatment, followed by a sharp increase in nestling survival from 4 years in treatment onwards (Figure 5). We found no terminal effects for reproduction traits, but previously reported terminal declines in telomere length (Salomons et al, 2009) and social dominance (Verhulst, Geerdink, Salomons, & Boonekamp, 2014) in this population. The heterogeneity in treatment effect is reminiscent of heterogeneity in age‐specific patterns of reproductive success among reproductive traits in vertebrates (Bouwhuis & Vedder, 2017; Hayward et al, 2015) and also in wild insects (Rodríguez‐Muñoz et al, 2019), and perhaps has the same explanation.…”

Canalization of development reduces the utility of traits as fitness biomarkers: feather fault bars in nestling birds

“…Details of this trade‐off remain to be identified, but given that social dominance in jackdaws, which depends on size (Verhulst et al . ), is important for sons only (Röell ), we speculate that sons prioritize growth more over plumage quality than daughters.…”

Life history evolution, reproduction, and the origins of sex‐dependent aging and longevity

“…Evolutionary theories of aging, and the disposable soma theory in particular, view the timing and rate of senescence as life history traits influenced by the optimization of these trade‐offs. Evidence, including from wild free‐living populations, supports the idea that resource allocation to reproduction in early adulthood trades off with somatic maintenance and late‐life performance. But the notion of direct allocation of resources to survival at the expense of reproduction, or vice versa, is being challenged by the complexities emerging from detailed laboratory studies of mechanistic pathways involved in aging …”