Constant mortality and fertility over age in Hydra

Senescence, the increase in mortality and decline in fertility with age after maturity, was thought to be inevitable for all multicellular species capable of repeated breeding. Recent theoretical advances and compilations of data suggest that mortality and fertility trajectories can go up or down, o...

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Published inProceedings of the National Academy of Sciences - PNAS Vol. 112; no. 51; pp. 15701 - 15706
Main Authors Schaible, Ralf, Scheuerlein, Alexander, Dańko, Maciej J, Gampe, Jutta, Martínez, Daniel E, Vaupel, James W
Format Journal Article
LanguageEnglish
Published United States National Acad Sciences 22.12.2015
National Academy of Sciences
Subjects
Animals
Biological Evolution
Biological Sciences
Evolution
Fertility
Hydra - physiology
Life Expectancy
Mortality
Stem cells
aging
biodemography
clonal reproduction
invertebrates
nonsenescence
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Summary:Senescence, the increase in mortality and decline in fertility with age after maturity, was thought to be inevitable for all multicellular species capable of repeated breeding. Recent theoretical advances and compilations of data suggest that mortality and fertility trajectories can go up or down, or remain constant with age, but the data are scanty and problematic. Here, we present compelling evidence for constant age-specific death and reproduction rates in Hydra, a basal metazoan, in a set of experiments comprising more than 3.9 million days of observations of individual Hydra. Our data show that 2,256 Hydra from two closely related species in two laboratories in 12 cohorts, with cohort age ranging from 0 to more than 41 y, have extremely low, constant rates of mortality. Fertility rates for Hydra did not systematically decline with advancing age. This falsifies the universality of the theories of the evolution of aging that posit that all species deteriorate with age after maturity. The nonsenescent life history of Hydra implies levels of maintenance and repair that are sufficient to prevent the accumulation of damage for at least decades after maturity, far longer than the short life expectancy of Hydra in the wild. A high proportion of stem cells, constant and rapid cell turnover, few cell types, a simple body plan, and the fact that the germ line is not segregated from the soma are characteristics of Hydra that may make nonsenescence feasible. Nonsenescence may be optimal because lifetime reproduction may be enhanced more by extending adult life spans than by increasing daily fertility.
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1R.S. and A.S. contributed equally to this work.
Reviewers: T.B.L.K., Newcastle University; R.E.S., University of California, Irvine; and K.W.W., University of California, Berkeley.
Contributed by James W. Vaupel, October 28, 2015 (sent for review April 4, 2015; reviewed by Thomas B. L. Kirkwood, Robert E. Steele, and Kenneth W. Wachter)
Author contributions: R.S., J.G., D.E.M., and J.W.V. designed research; R.S. and D.E.M. performed research; A.S., M.J.D., and J.G. analyzed data; and R.S., A.S., and J.W.V. wrote the paper.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.1521002112