Kooijman S A L M, Auger P, Poggiale J C, Kooi B W
Department of Theoretical Biology, Institute of Ecological Science, Vrije Universiteit, de Boelelaan 1087, 1081 HV Amsterdam, The Netherlands.
Biol Rev Camb Philos Soc. 2003 Aug;78(3):435-63. doi: 10.1017/s1464793102006127.
The merging of two independent populations of heterotrophs and autotrophs into a single population of mixotrophs has occurred frequently in evolutionary history. It is an example of a wide class of related phenomena, known as symbiogenesis. The physiological basis is almost always (reciprocal) syntrophy, where each species uses the products of the other species. Symbiogenesis can repeat itself after specialization on particular assimilatory substrates. We discuss quantitative aspects and delineate eight steps from two free-living interacting populations to a single fully integrated endosymbiotic one. The whole process of gradual interlocking of the two populations could be mimicked by incremental changes of particular parameter values. The role of products gradually changes from an ecological to a physiological one. We found conditions where the free-living, epibiotic and endobiotic populations of symbionts can co-exist, as well as conditions where the endobiotic symbionts outcompete other symbionts. Our population dynamical analyses give new insights into the evolution of cellular homeostasis. We show how structural biomass with a constant chemical composition can evolve in a chemically varying environment if the parameters for the formation of products satisfy simple constraints. No additional regulation mechanisms are required for homeostasis within the context of the dynamic energy budget (DEB) theory for the uptake and use of substrates by organisms. The DEB model appears to be dosed under endosymbiosis. This means that when each free-living partner follows DEB rules for substrate uptake and use, and they become engaged in an endosymbiotic relationship, a gradual transition to a single fully integrated system is possible that again follows DEB rules for substrate uptake and use.
在进化史上，两个独立的异养生物和自养生物种群合并为一个单一的混合营养生物种群的情况频繁发生。这是一大类相关现象的一个例子，这类现象被称为共生起源。其生理基础几乎总是（相互的）互养，即每个物种利用另一个物种的产物。在特定同化底物上特化后，共生起源可以重复发生。我们讨论了定量方面，并描述了从两个自由生活的相互作用种群到一个完全整合的内共生种群的八个步骤。两个种群逐渐相互关联的整个过程可以通过特定参数值的增量变化来模拟。产物的作用逐渐从生态作用转变为生理作用。我们发现了共生体的自由生活、体表共生和体内共生种群能够共存的条件，以及体内共生体胜过其他共生体的条件。我们的种群动力学分析为细胞内稳态的进化提供了新的见解。我们展示了如果产物形成的参数满足简单约束，具有恒定化学成分的结构生物量如何在化学变化的环境中进化。在动态能量预算（DEB）理论的背景下，生物体对底物的摄取和利用不需要额外的调节机制来维持内稳态。DEB模型在内共生情况下似乎是定量的。这意味着当每个自由生活的伙伴遵循DEB规则进行底物摄取和利用，并且它们建立起内共生关系时，有可能逐渐过渡到一个再次遵循DEB规则进行底物摄取和利用的单一完全整合系统。
