4) The role of microbial oscillations in animal senescence
Understanding rates of animal senescence is crucial for predicting demographic processes, and the mechanisms underpinning senescence is an active area of research 88–90. Whilst ecological research on animal senescence has focused on changes to immunity91, telomeres 92, stress hormones93, and gut microbiota composition24, research on humans and primates have demonstrated that an additional characteristic of ageing is the dampening of circadian rhythms 93–95, leading to disrupted sleep-wake cycles and physiology. Changes to gut microbiome rhythmicity with age are implicated in this process 96–98.
The involvement of microbial oscillations in senescence suggests that microbial oscillations should decline in old age (Fig. 3), yet this has rarely been tested in either captive or wild settings. In wild meerkats, there was little evidence for microbial senescence with old meerkats demonstrating microbial rhythms that were as strong as younger individuals 26. However, it is unclear whether meerkats are a good model system for ageing because only dominant individuals reach old age, and these individuals enjoy the benefits of group living and alpha status, potentially slowing senescence88. Exploiting systems with high survival rates, such as seabirds, may help clarify this question.