From microbes to mammals: The experimental evolution of aging and longevity across species.

Senescence, the functional deterioration of cells or organisms associated with increased age, is pervasive across the tree of life. Yet our understanding of the genetic and physiological basis underlying age-related declines in health and reproduction remains limited. Experimental evolution allows empirical examination of the question of why aging occurs; imposing selection for age-specific fitness traits shifts patterns of aging in experimental populations, enabling investigations of the variation underlying senescence and the mechanisms governing it. Whole-genome sequencing of experimentally evolved populations may reveal candidate genomic variants underlying particular aging patterns; unfortunately, most study systems suffer from limitations that weaken associations between genotypes and phenotypes. In this review, we provide a survey of experimental evolution studies that have altered population-level patterns of reproductive timing and senescence in a variety of species. We discuss the specific selection conditions that have increased longevity, the phenotypic responses and trade-offs that accompany these increases, and examine genomic data collected from these experiments. Additionally, we consider how selected field studies complement laboratory experiments on life-history evolution. Finally, we address the strengths and weaknesses of existing study systems, and evaluate which model organisms appear most promising for future genomic investigations of the evolutionary biology of aging.