Reproductive costs of heat shock protein in transgenic Drosophila melanogaster

Senescence may evolve when genes have antagonistic effects between early re production and later age-specific mortality. Although widely consistent wit h data of quantitative genetics, this model has yet to be validated with th e identification of a specific locus presenting such trade-offs. The molecu lar chaperone hsp70 may be a candidate for such a gene. Heat induced expres sion of the Hsp70 protein in adults decreases rates of age-specific mortali ty during normal aging, while maternally experienced heat shock depresses t he production of mature progeny. Here we show that maternal heat shock redu ces the proportion of egg hatch but not the viability of successfully hatch ed offspring. To assess whether heat induced maternal expression of hsp70 c auses reduced egg hatch, we measured the proportion of eggs that hatch from females engineered to overexpress hsp70 transgenes. We used the same trans genic strains that extend longevity upon hsp70 expression and found that Hs p70 is sufficient to suppress egg hatch. The proportion of egg hatch as a f unction of hsp70 expression was not reduced in the first eggs laid after ma ternal heat shock, but appears in later laid eggs, which were at preoogenic and early vitellogenic stages during the maternal expression of hsp70. The contervailing effects of hsp70 upon fecundity and subsequent age-specific mortality exemplify antagonistic pleiotropy, and this trade-off could contr ibute to the evolution of Drosophila senescence.