A life history model of indeterminate growth, somatic maintenance, and negative senescence

The wire material reports on a study that proposes a life history model explaining the phenomena of indeterminate growth, somatic maintenance, and negative senescence in certain organisms. Negative senescence refers to a decline in mortality and an increase in fecundity following sexual maturity.

Traditionally, aging has been attributed to a preferential allocation of resources towards reproduction over somatic maintenance. However, this study aims to bridge models of indeterminate growth with the concept of negative senescence by integrating somatic maintenance as a competing allocation decision alongside growth and reproduction.

The authors develop a life history model where an individual allocates energy among reproduction, somatic growth, and somatic maintenance. They demonstrate that negative actuarial senescence - a situation where mortality declines with age - arises when the proportional change in reproductive value outpaces the proportional change in fitness returns from current investments in reproduction and somatic maintenance.

To support their findings, the researchers employ invasion analysis and Pontryagin's maximum principle, and conduct numerical examinations of biologically relevant cases. Their results reveal that both negative senescence and indeterminate growth can coexist as uninvadable outcomes, even when somatic maintenance competes for the same resources as growth and reproduction.

Interestingly, the study also shows that the presence of diminishing returns to both reproduction and growth can lead to negative senescence. This finding extends the disposable soma theory, which traditionally applies to organisms with determinate growth, to organisms with indeterminate growth. The research identifies critical mechanisms behind the observed association between indeterminate growth and non-senescent demographic trajectories in various species.