A. Blarer et al., DIAGNOSING SENESCENCE - INFERRING EVOLUTIONARY CAUSES FROM PHENOTYPICPATTERNS CAN BE MISLEADING, Proceedings - Royal Society. Biological Sciences, 262(1365), 1995, pp. 305-312
Based on the predictions of two theories for the evolution of senescen
ce, the 'antagonistic pleiotropy' and the 'mutation accumulation' theo
ry, an age-specific increase in mortality and a decrease in fecundity
are widely used criteria to diagnose senescence in natural and laborat
ory populations. In this study we question the reliability of these cr
iteria. Using a simple model we show that similar phenotypic patterns
result from optimal life histories without senescence. With a tradeoff
between reproduction and period survival, optimal life histories prod
uce patterns of increasing mortality and decreasing fecundity as organ
isms age, even if the tradeoff does not deteriorate with age, so that
we are not forced to invoke genetic effects such as antagonistic pleio
tropy or accumulation of deleterious mutations to explain such pattern
s. Furthermore, if optimal life history theory is applied to senescent
organisms, phenotypic patterns can result that are usually not associ
ated with senescence. We conclude that the reliability of a diagnosis
of senescence based on phenotypic patterns and the comprehension of th
e phenomenon senescence depends critically on understanding to what ex
tent tradeoffs are determined by the effects of segregating genes.