Life History Trade-Offs Modulate the Speed of Senescence

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The vast amount of scientific attention attracted by ageing research is, to a large extent, due to humanity's desire to prolong life span and 'health span'. Still, from a purely ecological and evolutionary point of view, the fact that such a large diversity of longevities exists is extremely puzzling and worthy of investigation in itself. We used two open-data repositories of high-quality demographic information for animals and plants to present a novel overview of the degree of variation in life history strategies and their component life history traits, including the speed of senescence, which we evaluate here as the time elapsed from mean age at maturity to the age at which 99 per cent of the individuals in an examined cohort are dead. We explored how life history traits and strategies are associated with the speed of senescence across 571 species of animals and plants. We found that the speed of senescence varies dramatically across the Tree of Life and that it has a moderately strong phylogenetic signal when considering both plants and animals but that this signal is stronger in animals than in plants, indicating that the strength of selection on the trait may differ between kingdoms. We next examined how key life history traits such as mean life expectancy, generation time and the length of life lived before maturity correlate with this measure of senescence, finding that iteroparous, slow-growing species are more likely to senesce slowly and thus attain long mature life spans. We further examined the speed of senescence at two taxonomic levels: Comparing kingdoms, with plants more likely to postpone senescence than animals, and, when the data allowed for it, comparing taxonomic classes, where we found that pine trees are particularly slow to senesce, followed by reptiles and sponges. Most mammals, birds and the vast majority of fish in our analyses senesce rapidly.