Briga, Michael ; Verhulst, Simon
In humans and in wild mammals and birds, the functioning of our bodies declines with age. Understanding how our organisms age and how this ageing associates with lifespan is crucial for improving our quality of life and lifespan.
Our rate of energy consumption or metabolism determines many aspects of our activity, physiology, behaviour and personality. We know that in mammals and birds, minimal energy consumption when resting declines with age. However, previous studies have done measured this energy consumption only at warm ambient temperatures. No studies have quantified how minimal energy consumption resting changes with age at the colder ambient temperatures that mammals and birds commonly experience in nature.
Here we study the change of the minimal energy consumption at rest in a small bird, the zebra finch. We made thousands of measurements on hundreds of birds at night while the bird were sleeping. We did so at the standard warm ambient temperatures that such measurements are done and at the everyday colder temperatures. We confirmed previous studies that at the standard warm ambient temperatures energy consumption declines with age. In contrast, at the colder every day temperatures, the minimal energy consumption increased with age. Most importantly, we showed that the rate of ageing of minimal energy consumption at these two different temperatures were completely independent. Hence, metabolism at one temperature cannot be used as a proxy for the other.
Our study shows that, in contrast to the current view, that minimal energy requirements increase with age and illustrate the importance of studying the ageing phenotype in a realistic environmental setting.