Abstract
One of the most striking patterns in comparative biology is the negative correlation between lifespan and fecundity observed in comparisons among species. This pattern is consistent with the idea that organisms need to allocate a fixed energy budget among competing demands of growth, development, reproduction and somatic maintenance. However, exceptions to this pattern have been observed in many social insects, including ants, bees, and termites. In honey bees ( Apis mellifera), Vitellogenin ( Vg), a yolk protein precursor, has been implicated in mediating the long lifespan and high fecundity of queen bees. To determine if Vg-like proteins can regulate lifespan in insects generally, we examined the effects of expression of Apis Vg and Drosophila CG31150 (a Vg-like gene recently identified as cv-d) on Drosophila melanogaster lifespan and fecundity using the RU486-inducible GeneSwitch system. For all genotypes tested, overexpression of Vg and CG31150 decreased Drosophila lifespan and did not affect total or age-specific fecundity. We also detected an apparent effect of the GeneSwitch system itself, wherein RU486 exposure (or the GAL4 expression it induces) led to a significant increase in longevity and decrease in fecundity in our fly strains. This result is consistent with the pattern reported in a recent meta-analysis of Drosophila aging studies, where transgenic constructs of the UAS/GAL4 expression system that should have no effect (e.g. an uninduced GeneSwitch) significantly extended lifespan in some genetic backgrounds. Our results suggest that Vg-family genes are not major regulators of Drosophila life history traits, and highlight the importance of using appropriate controls in aging studies.
Highlights
Aging is an almost universal process in multicellular organisms, in which organismal function and performance decline with age1,2
Consistent with this idea of resource allocation trade-offs, lifespan and fecundity are generally negatively correlated in comparisons among species8,10, A prominent exception to this pattern occurs in many social insects
Quantitative PCR confirmed that Vg and CG31150 were overexpressed by the GeneSwitch system Flies carrying S106 GAL4 driver and each of the target genes, Vg-1, Vg-2, CG31150-2, CG31150-4, that were fed on RU486 had a >5 fold increase in target mRNA expression compared with their genetically matched controls (Table 1)
Summary
Aging (senescence) is an almost universal process in multicellular organisms, in which organismal function and performance decline with age. Patterns and rates of aging vary enormously among, and within species. Evolutionary life history (LH) theory generally assumes that allocation of energy among the competing demands of growth, development, reproduction and somatic maintenance lead to functional trade-offs among these processes. Evolutionary life history (LH) theory generally assumes that allocation of energy among the competing demands of growth, development, reproduction and somatic maintenance lead to functional trade-offs among these processes8,9 Consistent with this idea of resource allocation trade-offs, lifespan and fecundity are generally negatively correlated in comparisons among species, A prominent exception to this pattern occurs in many social insects. Termites, and bees, reproductive females are both long-lived and highly fecund relative to other species. Most non-social insects have adult longevity of less than one year, and have lower fecundity than social insect queens
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