Institute for Evolution and Biodiversity, Westfälische Wilhelms-Universität Münster, Münster, Germany.
Department of Agriculture, Università degli Studi Mediterranea di Reggio Calabria, Reggio Calabria, Italy.
Proc Biol Sci. 2022 Aug 10;289(1980):20221115. doi: 10.1098/rspb.2022.1115.
General evolutionary theory predicts that individuals in low condition should invest less in sexual traits compared to individuals in high condition. Whether this positive association between condition and investment also holds between young (high condition) and senesced (low condition) individuals is however less clear, since elevated investment into reproduction may be beneficial when individuals approach the end of their life. To address how investment into sexual traits changes with age, we study genes with sex-biased expression in the brain, the tissue from which sexual behaviours are directed. Across two distinct populations of we find that old brains display fewer sex-biased genes, and that expression of both male-biased and female-biased genes converges towards a sexually intermediate phenotype owing to changes in both sexes with age. We further find that sex-biased genes in general show heightened age-dependent expression in comparison to unbiased genes and that age-related changes in the sexual brain transcriptome are commonly larger in males than females. Our results hence show that ageing causes a desexualization of the fruit fly brain transcriptome and that this change mirrors the general prediction that low condition individuals should invest less in sexual phenotypes.
一般进化理论预测，低条件个体与高条件个体相比，应减少在性特征上的投入。然而，年轻（高条件）和衰老（低条件）个体之间的条件与投入之间是否存在这种正相关关系尚不清楚，因为当个体接近生命尽头时，增加对繁殖的投入可能是有益的。为了解释性特征的投入如何随年龄变化，我们研究了大脑中具有性别偏向表达的基因，即性行为所指向的组织。在两个不同的群体中，我们发现老年大脑显示出较少的性别偏向基因，并且由于两性随年龄的变化，雄性偏向和雌性偏向基因的表达都趋向于中间的性表型。我们进一步发现，与无偏基因相比，性别偏向基因通常表现出更高的年龄依赖性表达，并且性大脑转录组的与年龄相关的变化在雄性中通常比在雌性中更大。因此，我们的研究结果表明，衰老会导致果蝇大脑转录组去性化，这种变化反映了低条件个体应减少在性表型上投入的一般预测。
