Bilinski Tomasz, Bylak Aneta, Kukuła Krzysztof, Zadrag-Tecza Renata
Department of Biochemistry and Cell Biology, Faculty of Biology and Agriculture, University of Rzeszów, Rzeszów, Poland.
Department of Ecology and Environmental Protection; Institute of Agricultural Sciences, Land Management and Environmental Protection, University of Rzeszów, Rzeszów, Poland.
PeerJ. 2021 Nov 2;9:e12286. doi: 10.7717/peerj.12286. eCollection 2021.
Most common terrestrial animal clades exhibit senescence, suggesting strong adaptive value of this trait. However, there is little support for senescence correlated with specific adaptations. Nevertheless, insects, mammals, and birds, which are the most common terrestrial animal clades that show symptoms of senescence, evolved from clades that predominantly did not show symptoms of senescence. Thus, we aimed to examine senescence in the context of the ecology and life histories of the main clades of animals, including humans, and to formulate hypotheses to explain the causes and origin of senescence in the major clades of terrestrial animals.
We reviewed literature from 1950 to 2020 concerning life expectancy, the existence of senescence, and the adaptive characteristics of the major groups of animals. We then proposed a relationship between senescence and environmental factors, considering the biology of these groups of animals. We constructed a model showing the phylogenetic relationships between animal clades in the context of the major stages of evolution, distinguishing between senescent and biologically 'immortal' clades of animals. Finally, we synthesised current data on senescence with the most important concepts and theories explaining the origin and mechanisms of senescence. Although this categorisation into different senescent phenotypes may be simplistic, we used this to propose a framework for understanding senescence.
We found that terrestrial mammals, insects, and birds show senescence, even though they likely evolved from non-senescent ancestors. Moreover, secondarily aquatic animals show lower rate of senescence than their terrestrial counterparts. Based on the possible life histories of these groups and the analysis of the most important factors affecting the transition from a non-senescent to senescent phenotype, we conclude that aging has evolved, not as a direct effect, but as a correlated response of selection on developmental strategies, and that this occurred separately within each clade. Adoption of specific life history strategies could thus have far-reaching effects in terms of senescence and lifespan.
Our analysis strongly suggests that senescence may have emerged as a side effect of the evolution of adaptive features that allowed the colonisation of land. Senescence in mammals may be a compromise between land colonisation and longevity. This hypothesis, is supported by palaeobiological and ecological evidence. We hope that the development of new research methodologies and the availability of more data could be used to test this hypothesis and shed greater light on the evolution of senescence.
大多数常见的陆生动物类群都表现出衰老现象，这表明该特征具有很强的适应性价值。然而，几乎没有证据支持衰老与特定适应性之间存在关联。尽管如此，昆虫、哺乳动物和鸟类是最常见的表现出衰老症状的陆生动物类群，它们是从主要不表现出衰老症状的类群进化而来的。因此，我们旨在从包括人类在内的主要动物类群的生态和生活史背景下研究衰老现象，并提出假设来解释陆生动物主要类群衰老的原因和起源。
我们回顾了1950年至2020年有关动物主要类群的预期寿命、衰老的存在以及适应性特征的文献。然后，考虑到这些动物类群的生物学特性，我们提出了衰老与环境因素之间的关系。我们构建了一个模型，展示了在进化的主要阶段背景下动物类群之间的系统发育关系，区分了衰老的和生物学上“不朽”的动物类群。最后，我们将当前关于衰老的数据与解释衰老起源和机制的最重要概念和理论进行了综合。尽管这种划分为不同衰老表型的方法可能过于简单，但我们以此提出了一个理解衰老的框架。
我们发现陆生哺乳动物、昆虫和鸟类都表现出衰老现象，尽管它们可能是从非衰老的祖先进化而来的。此外，次生水生动物的衰老速度比它们的陆生同类要低。基于这些类群可能的生活史以及对影响从非衰老表型向衰老表型转变的最重要因素的分析，我们得出结论，衰老的进化并非直接效应，而是选择对发育策略的相关反应，并且这种情况在每个类群中是分别发生的。因此，采用特定的生活史策略可能会对衰老和寿命产生深远影响。
我们的分析有力地表明，衰老可能是作为使陆地得以殖民化的适应性特征进化的副作用而出现的。哺乳动物的衰老可能是陆地殖民化和长寿之间的一种权衡。这一假设得到了古生物学和生态学证据的支持。我们希望新研究方法的发展以及更多数据的可得性能够用于检验这一假设，并为衰老的进化提供更多的启示。
