Extended longevity lines of Drosophila melanogaster: Abundance of yolk protein gene mRNA in fat body and ovary

Lines of Drosophila melanogaster selected for late-life female reproduction typically exhibit correlated reponses of reduced early fecundity and incre ased longevity. This relationship suggests a tradeoff between reproductive effort and somatic maintenance, which in turn, underlies some evolutionary theories of senescence. The mechanistic basis of the apparent tradeoff betw een increased longevity and reduced early-age fecundity has remained obscur e. The present manuscript addresses the issues of whether the reduced early -age fecundity in selected lines corresponds to reduced yolk-protein mRNA p roduction, and whether long-lived flies exhibit somatic maintenance in term s of relatively reduced yolk-protein mRNA production in the fat body. Yolk protein is one of the most abundant proteins used for female reproduction. By comparing a set of lines selected for late life reproduction with the co rresponding control lines, we show that that yolk-protein gene mRNA relativ e abundance during the first four days posteclosion did not correspond to r educed early-life fecundity in the selected lines. In D. melanogaster,, yol k protein is produced in the fat body and ovarian follicle cells. On the fo urth day posteclosion, relatively more yolk-protein gene mRNA was present i n the fat body. On day 1 posteclosion, supplemental yeast did not alter rel ative yolk-protein gene mRNA abundance. However, on day 4 posteclosion, sup plemental yeast stimulated yolk-protein gene mRNA production in the fat bod y, which suggests an underlying mechanism for the nutrition-based phenotypi c plasticity of fecundity previously documented in these lines. On medium w ithout supplemental yeast, the relatively low abundance of fat body yolk-pr otein gene mRNA in the selected lines on day 4 posteclosion corresponds to a prediction derived from the disposable soma theory. (C) 1999 Elsevier Sci ence Inc. All rights reserved.