Cooperative care slows offspring telomere attrition and buffers growth against variable rainfall in a wild Kalahari bird

Recent studies suggest that early-life competition can compromise somatic integrity and exacerbate late-life declines in performance (senescence). However, the potentially beneficial effects for somatic integrity of early-life receipt of cooperation remain poorly understood. Here we investigate how the receipt of cooperative alloparental care impacts developmental telomere dynamics (a biomarker of somatic integrity) and growth in cooperatively breeding white-browed sparrow weavers, Plocepasser mahali. In sparrow-weaver groups, a single breeding pair monopolize reproduction, non-breeding helpers assist with nestling provisioning, and both helper number and rainfall (in this semi-arid environment) positively predict nestling provisioning rate. Accordingly, we show that nestlings reared by more helpers enjoy (i) slower telomere attrition rates (known to predict downstream survival in this species), and (ii) higher growth rates, which are also buffered against variation in rainfall (owing to stronger beneficial effects of helpers in dry conditions). These relationships cannot be readily attributed to correlated variation in maternal egg investment or among-territory variation in food availability. These findings provide rare evidence that alloparental care can bolster the somatic integrity of offspring, highlighting the potential for downstream effects on their senescence trajectories. Our findings have implications too for understanding the resilience of cooperative species in increasingly unpredictable rainfall regimes. This article is part of the theme issue 'Developmental circuits in ageing'.