Resource availability, maternal effects, and longevity.

Experiments with a clone of the cladoceran Daphnia pulex indicate that the nutritional conditions of the maternal environment play a major role in determining the progeny's phenotype. Apparently, by influencing the physiology and/or morphology of individuals during early development, maternal investment not only enhances juvenile survival but has long-lasting, favorable effects on the progeny's ability to convert resources into growth and reproduction as well as negative repercussions for adult survival of the progeny. Life-span may also be radically altered by modifying food schedules within an individual's life. Neither reproductive effort nor rate of living hypotheses can explain longevity variation within Daphnia clones; rather the onset of senescence appears to be associated with a general breakdown in the ability to incorporate energy into biomass. Analysis of our results as well as earlier data with a "rate of aging-threshold vitality" model suggests that increasing the availability of food to an individual increases the rate of aging while decreasing the threshold vitality necessary for survival and that increasing maternal investment increases both the vitality at birth and the rate of aging of the progeny.