Evolution Of Long Lifespans Research Articles

Differential response to larval crowding of a long- and a short-lived medfly biotype.

Response of endophytic fruit fly species (Tephritidae) to larval crowding is a form of scramble competition that may affect important life history traits of adults, such as survival and reproduction. Recent empirical evidence demonstrates large differences in adult life history traits, especially longevity, among Mediterranean fruit fly (Ceratitis capitata; "medfly") biotypes obtained from different regions of the world. However, whether the evolution of long lifespan is associated with response to stress induced by larval crowding has not been fully elucidated. We investigated, under constant laboratory conditions, the response of a short- and a long-lived medfly biotypes to stress induced by larval crowding. Survival and development of larvae and pupae and the size of resulting pupae were recorded. The lifespan and age-specific egg production patterns of the obtained adults were recorded. Our findings reveal that increased larval density reduced immature survival (larvae and pupae) in the short-lived biotype but had rather neutral effects on the longed-lived one. Only larvae of the long-lived biotype were capable of prolonging their developmental duration under the highest crowding regime to successfully pupate and emerge as adults. Response of emerging adults to larvae crowding conditions was similar in the two medfly biotypes. Those individuals emerging from high larval density regimes had reduced longevity and fecundity. Long-lived biotype individuals, however, appeared to suffer a higher cost in longevity compared with the short-lived one. The importance of our findings to understand the evolution of long lifespan is discussed.

Encephalization and longevity evolved in a correlated fashion in Euarchontoglires but not in other mammals.

Across mammals, encephalization and longevity show a strong correlation. It is not clear, however, whether these traits evolved in a correlated fashion within mammalian orders, or when they do, whether one trait drives changes in the other. Here, we compared independent and correlated evolutionary models to identify instances of correlated evolution within six mammalian orders. In cases of correlated evolution, we subsequently examined transition patterns between small/large relative brain size and short/long lifespan. In four mammalian orders, these traits evolved independently. This may reflect constraints related to energy allocation, predation avoidance tactics, and reproductive strategies. Within both primates and rodents, and their parent clade Euarchontoglires, we found evidence for correlated evolution. In primates, transition patterns suggest relatively larger brains likely facilitated the evolution of long lifespans. Because larger brains prolong development and reduce fertility rates, they may be compensated for with longer lifespans. Furthermore, encephalization may enable cognitively-complex strategies that reduce extrinsic mortality. Rodents show an inverse pattern of correlated evolution, whereby long lifespans appear to have facilitated the evolution of relatively larger brains. This may be because longer lived organisms have more to gain from investment in encephalization. Together, our results provide evidence for the correlated evolution of encephalization and longevity, but only in some mammalian orders.

Slow development as an evolutionary cost of long life

Summary Life‐history theory predicts a trade‐off between early‐life fitness and life span. While the focus traditionally has been on the fecundity‐life span trade‐off, there are strong reasons to expect trade‐offs with growth rate and/or development time. We investigated the roles of growth rate and development time in the evolution of life span in two independent selection experiments in the outcrossing nematode Caenorhabditis remanei. First, we found that selection under heat‐shock leads to the evolution of increased life span without fecundity costs, but at the cost of slower development. Thereafter, the putative evolutionary links between development time, growth rate, fecundity, heat‐shock resistance and life span were independently assessed in the second experiment by directly selecting for fast or slow development. This experiment confirmed our initial findings, since selection for slow development resulted in the evolution of long life span and increased heat‐shock resistance. Because there were no consistent trade‐offs with growth rate or fecundity, our results highlight the key role of development rate – differentiation of the somatic cells per unit of time – in the evolution of life span. Since development time is under strong selection in nature, reduced somatic maintenance resulting in shorter life span may be a widespread cost of rapid development. A lay summary is available for this article.