Everyone is aware that the world’s population is ageing and thus interest in the evolution of ageing has never been higher. Understanding how ageing affects physiology, survival and reproduction also has consequences for population dynamics and responses to environmental change. By understanding how and why individuals vary in their ageing rates, and how different aspects of physiology and phenotype change differently with age, we can better understand these dynamics.
My PhD work showed that early-life stress accelerated senescence in parasite resistance in Soay sheep, and that patterns of ageing varied across four different reproductive traits in females. I have continued work along this theme by determining factors associated with ageing rates in longer-lived animals, including work on a semi-captive Asian elephant population in Myanmar (Burma), as well as the Finnish data set. I aim to test the hypothesis that variation in ageing rates is linked to early-life investment in reproduction and early exposure to adverse environments, including scarce resources and disease epidemics.
My most recent work focuses on the question of whether senescence is synchronous or not, and how selection may have shaped (a)synchrony of senescence. The only available evolutionary theory predicts that all traits and biological systems should age at the same rate, but this theory is over 50 years old and, crucially, there is lots of evidence in wild and lab populations showing that different traits senescence at different rates. We gathered data on 20 different traits, from survival and reproduction to growth, size, behaviour and parasite resistance, in the Soay sheep to test for variation in patterns of senescence. Our data showed that senescence patterns were highly variable, with different traits measured in the two sexes showing high variable rates of ageing. Future work should focus on estimating age-specific selection pressures and quantitative genetic parameters in this and other similar wild populations.