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Die Arbeitsgruppe von Ralph Gräf befasst sich mit der Rolle der Mikrotubuli bei dynamischen Bewegungsvorgängen der Zelle. Mikrotubuli sind röhrenförmige Elemente des Zellskeletts, die alle von einem zentralen Ort in der Nähe des Zellkerns, dem Centrosom, auswachsen und von dort organisiert werden. Neben ihrer Funktion als Transportweg für zahlreiche Substanzen und Zellorganelle spielen sie eine zentrale Rolle bei der Zellteilung, indem sie mit dafür sorgen, dass die Erbsubstanz korrekt auf die Tochterzellen verteilt wird. Den Schwerpunkt der Forschungsarbeiten bildet die Charakterisierung neuer Komponenten des Centrosoms und neuer Mikrotubuli- bindender Proteine im einfachen Modellsystem der Dictyostelium Amöbe. Diese Arbeiten sind von großer Bedeutung für die Erklärung Zellskelett-assoziierter Krankheiten und Störungen der geordneten Zellteilung, wie sie beispielsweise in Krebszellen auftritt.
According to resource allocation theory, animals face a trade off between the allocation of resources into reproduction and into individual growth/maintenance. This trade off is reinforced when food conditions decline. It is well established in biological research that many animals increase their life span when food is in suboptimal supply for growth and/or reproduction. Such a situation of reduced food availability is called dietary restriction. An increase in life span under dietary restricted conditions is seen as a strategy to tolerate periods of food shortage so that the animals can start reproduction again when food is in greater supply. In this study, the effect of dietary restriction on life span and reproduction in two rotifer species, Cephalodella sp. and Elosa worallii, was investigated using life table experiments. The food concentration under dietary restricted conditions was below the threshold for population growth. It was (1) tested whether the rotifers start reproduction again after food replenishment, and (2) estimated whether the time scale of dietary restricted conditions is relevant for the persistence of a population in the field. Only E. worallii responded to dietary restriction with an increase in life span at the expense of reproduction. After replenishment of food, E. worallii started to reproduce again within I day. With an increase in the duration of dietary restricted conditions of up to 15 days, which is longer than the median life span of E. worallii under food saturation, the life span increased and the life time reproduction decreased. These results suggest that in a temporally (or spatially) variable environment, some rotifer populations can persist even during long periods of severe food deprivation.