Understanding determinants of individual variation in senescence in a natural population

点击翻译按钮获取中文摘要

As individuals reach older ages their bodies deteriorate - at the cellular to whole body level - a process known as senescence. It is clear that individuals differ greatly in the age at which they start to senesce, and how quickly they then deteriorate. For example, a study of 38-year-old humans reported biological ages (i.e. a measure of the intrinsic condition / health of the individual rather than how long they have been alive) that varied from 28 to 61 years. However, why individuals senesce so differently remains unresolved. Indeed, this is one of the biggest unanswered questions in evolutionary biology. This has massive ramifications for health and (our ageing) society, as individuals/populations could reduce exposure to factors that negatively impact senescence so that individuals can live longer healthier lives, not to mention associated implications for animal breeding and conservation (see academic beneficiaries section).Understanding individual variation in senescence has been hampered by a focus on a limited number of characteristics, insufficient appropriate data to measure the genetic component of senescence, and a paucity of integrated studies in natural populations where environmental factors vary and natural and sexual selection act out. These points are important. Different characteristics (e.g. reproductive ability, immunological defences, physical condition) may senesce differently, and variation in the genetic makeup of individuals may underpin different individual responses. The age of an individual's parents when it was born may also impact upon individual senescence, or reproduction early in life may affect ability to reproduce later in life. Crucially, in natural populations, environmental and social effects will combine to determine the stresses that individuals suffer, influence the expression of genetic variation, and ultimately impact on individual deterioration. Before we can mitigate the effect of deleterious factors we need to understand the relative contribution of these factors on senescence.We aim to help remedy these shortcomings by investigating the interacting environmental, social, (non-genetic) transgenerational and genetic determinants of individual patterns of senescence in a natural population. We can only now do this because we have a unique long-term data resource from a detailed study of a population of cooperatively breeding Seychelles warblers, Acrocephalus sechellensis. Crucially, this is an isolated island population, which has allowed us to follow all individuals (over many generations) throughout their lives, collect blood samples (thus allowing individual genetic characteristics and intrinsic biomarkers to be measured) and measure concurrent environmental conditions, social experiences and individual characteristics.We will use these data to measure individual variation in the onset and rate of senescence with unparalleled accuracy. We will quantify the impact of environmental, social, transgenerational (i.e. parental age) and genetic factors, across the genome, on when and how quickly individuals deteriorate with age. We will establish if trade-offs between different individual characteristics, and/or across different parts of an individual's life, determine patterns of senescence and whether there is a genetic basis to this. We will quantify the strength of selection on senescence. Finally, we will determine the overall relative impact that environmental, social, transgenerational and genetic effects have on individual senescence.This study will not only test many key predictions that will reveal the immediate causes of individual variation in senescence, it will also shed light on the ultimate reasons behind the evolution of senescence. Understanding which factors exacerbate senescence means we can potentially avoid such factors or conditions, which will be directly useful to human/veterinary medicine, society and conservation.