Nachtrag:
Ging schneller , als ich dachte:
Dietary restriction and aging: comparative tests of evolutionary hypotheses.
Kirk KL.
Department of Biology, New Mexico Tech, Socorro 87801, USA.
[email protected]
Dietary restriction (DR) increases life span in many types of animals. The response to chronic DR may be an adaptation to environments with variable food levels. This study uses the comparative method to test evolutionary predictions about the origin of the response to DR, using data from 10 species of rotifers. Most species, but not all, responded to DR by increasing mean life span, maximum life span, reproductive life span, mortality rate doubling time, and initial mortality rate. Interspecific comparisons did not show the predicted correlations between the strength of the response to DR and either reproductive life span, age of first reproduction, or total reproduction. There was support for the idea that the response to chronic DR is associated with changes in reproductive allocation during short-term periods of starvation: species that reduced reproduction when starved increased their life spans under DR, whereas species that continued to reproduce when starved decreased their life spans under DR.
Calorie restriction and aging: a life-history analysis.
Shanley DP, Kirkwood TB.
University of Newcastle, Institute for the Health of the Elderly, Wolfson Research Centre, Newcastle General Hospital, Newcastle Upon Tyne, United Kingdom.
[email protected]
The disposable soma theory suggests that aging occurs because natural selection favors a strategy in which fewer resources are invested in somatic maintenance than are necessary for indefinite survival. However, laboratory rodents on calorie-restricted diets have extended life spans and retarded aging. One hypothesis is that this is an adaptive response involving a shift of resources during short periods of famine away from reproduction and toward increased somatic maintenance. The potential benefit is that the animal gains an increased chance of survival with a reduced intrinsic rate of senescence, thereby permitting reproductive value to be preserved for when the famine is over. We describe a mathematical life-history model of dynamic resource allocation that tests this idea. Senescence is modeled as a change in state that depends on the resources allocated to maintenance. Individuals are assumed to allocate the available resources to maximize the total number of descendants. The model shows that the evolutionary hypothesis is plausible and identifies two factors, both likely to exist, that favor this conclusion. These factors are that survival of juveniles is reduced during periods of famine and that the organism needs to pay an energetic "overhead" before any litter of offspring can be produced. If neither of these conditions holds, there is no evolutionary advantage to be gained from switching extra resources to maintenance. The model provides a basis to evaluate whether the life-extending effects of calorie-restriction might apply in other species, including humans.
tschö,
Philipp