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.