Body mass aging trajectory is modulated by environmental conditions but independent of lifespan
How lifespan associates with aging trajectories of health and disease is an urgent question in societies with increasing lifespan. Body mass declines with age are associated with decreased organismal functioning in many species. We tested whether two factors that decreased lifespan in zebra finches, sex and manipulated environmental quality, accelerated the onset and/or rate of within-individual body mass declines. We subjected 597 birds for nine years to experimentally manipulated foraging costs (harsh = H, benign = B) during development and in adulthood in a 2x2 design. This yielded four treatment combinations (HH, HB, BH, BB). Harsh environments during development and in adulthood decreased average body mass additively. In males, the aging trajectory was quadratic, with a maximum between 3.5 and 4 years, and independent of the environment (HH=HB=BH=BB). In females, the shape of the aging trajectory differed between environments: a quadratic trajectory as in males in the benign adult environment (HB=BB), a linear decline when benign development was followed by harsh adulthood (BH) and a linear increase when in a lifelong harsh environment (HH). We found no evidence for an association between lifespan and body mass aging trajectories either between or within experimental groups. However, females lived shorter than males, and their body mass decline started earlier for most treatment combinations. Thus, we conclude that foraging conditions can affect the shape of body mass aging trajectories, but these are independent of lifespan.