Institute for Evolution and Biodiversity, University of Münster, Germany.
Institut für Zoologie/Evolutionsbiologie, University of Regensburg, Germany.
Genome Biol Evol. 2021 Jun 8;13(6). doi: 10.1093/gbe/evab093.
Evolutionary theories of ageing predict a reduction in selection efficiency with age, a so-called "selection shadow," due to extrinsic mortality decreasing effective population size with age. Classic symptoms of ageing include a deterioration in transcriptional regulation and protein homeostasis. Understanding how ant queens defy the trade-off between fecundity and lifespan remains a major challenge for the evolutionary theory of ageing. It has often been discussed that the low extrinsic mortality of ant queens, that are generally well protected within the nest by workers and soldiers, should reduce the selection shadow acting on old queens. We tested this by comparing strength of selection acting on genes upregulated in young and old queens of the ant, Cardiocondyla obscurior. In support of a reduced selection shadow, we find old-biased genes to be under strong purifying selection. We also analyzed a gene coexpression network (GCN) with the aim to detect signs of ageing in the form of deteriorating regulation and proteostasis. We find no evidence for ageing. In fact, we detect higher connectivity in old queens indicating increased transcriptional regulation with age. Within the GCN, we discover five highly correlated modules that are upregulated with age. These old-biased modules regulate several antiageing mechanisms such as maintenance of proteostasis, transcriptional regulation, and stress response. We observe stronger purifying selection on central hub genes of these old-biased modules compared with young-biased modules. These results indicate a lack of transcriptional ageing in old C. obscurior queens, possibly facilitated by strong selection at old age and well-regulated antiageing mechanisms.
衰老的进化理论预测，随着年龄的增长，由于外源性死亡率随年龄的增长而降低有效种群大小，选择效率会降低，即所谓的“选择阴影”。衰老的典型症状包括转录调控和蛋白质动态平衡的恶化。理解蚁后如何违背繁殖力和寿命之间的权衡，仍然是衰老进化理论的一个主要挑战。人们经常讨论的是，蚁后的外源性死亡率低，由于工蚁和兵蚁在巢内对蚁后提供了很好的保护，这应该会降低作用于老年蚁后的选择阴影。我们通过比较 Cardiocondyla obscurior 蚁的年轻和老年蚁后的上调基因所受选择的强度来验证这一点。支持选择阴影减弱的观点是，我们发现老偏向基因受到强烈的净化选择。我们还分析了一个基因共表达网络（GCN），旨在以调控和蛋白质动态平衡恶化的形式检测衰老的迹象。我们没有发现衰老的证据。事实上，我们发现老年蚁后的连接性更高，这表明随着年龄的增长，转录调控增强。在 GCN 中，我们发现了五个随着年龄增长而上调的高度相关模块。这些老偏向模块调节几种抗衰老机制，如蛋白质动态平衡的维持、转录调控和应激反应。与年轻偏向模块相比，我们观察到这些老偏向模块的中心枢纽基因受到更强的净化选择。这些结果表明，老年 C. obscurior 蚁后没有转录衰老，这可能是由于老年时选择强烈和调节良好的抗衰老机制所致。
