A simple model and rules for the evolution of microbial mutualistic symbiosis with positive fitness feedbacks

IF 1.2 4区 生物学 Q4 ECOLOGY Theoretical Population Biology Pub Date : 2024-10-09 DOI:10.1016/j.tpb.2024.09.002
Sosuke Iwai
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Abstract

The evolution of microbe–microbe mutualistic symbiosis is considered to be promoted by repeated exchanges of fitness benefits, which can generate positive fitness feedbacks (‘partner fidelity feedback’) between species. However, previous evolutionary models for mutualism have not captured feedback dynamics or coupling of fitness between species. Here, a simple population model is developed to understand the evolution of mutualistic symbiosis in which two microbial species (host and symbiont) continuously grow and exchange fitness benefits to generate feedback dynamics but do not strictly control each other. The assumption that individual microbes provide constant amounts of resources, which are equally divided among interacting partner individual, enables us to reveal a simple rule for the evolution of costly mutualism with positive fitness feedbacks: the product of the benefit-to-cost ratios for each species exceeds one. When this condition holds, high cooperative investment levels are favored in both species regardless of the amount invested by each partner. The model is then extended to examine how symbiont mutation, immigration, or switching affects the spread of selfish or cooperative symbionts, which decrease and increase their investment levels, respectively. In particular, when a host associates with numerous symbionts without enforcement, neither mutation nor immigration but rather random switching would allow the spread of cooperative symbionts. Examples using symbiont switching for evolution would include large ciliates hosting numerous intracellular endosymbionts. The simple model and rules would provide a basis for understanding the evolution of microbe–microbe mutualistic symbiosis with positive fitness feedbacks and without enforcement mechanisms.
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具有正能量反馈的微生物互助共生进化的简单模型和规则。
微生物-微生物互利共生的进化被认为是通过重复交换适合度利益而促进的,这可以在物种之间产生正的适合度反馈("伙伴忠诚度反馈")。然而,以往的互惠进化模型并没有捕捉到物种间的反馈动态或适合度耦合。在这里,我们建立了一个简单的种群模型来理解互惠共生的进化过程,在这个过程中,两个微生物物种(宿主和共生体)不断生长并交换适合度收益,从而产生反馈动态,但并不严格控制对方。假定单个微生物提供恒定数量的资源,这些资源在相互作用的伙伴个体之间平均分配,这使我们能够揭示出具有正能量反馈的高成本互利共生进化的一个简单规则:每个物种的收益-成本比的乘积超过 1。当这一条件成立时,无论每个伙伴的投资额是多少,两个物种都会倾向于高合作投资水平。然后,我们将模型扩展到研究共生体变异、移民或转换如何影响自私共生体或合作共生体的传播,从而分别降低和提高它们的投资水平。特别是,当宿主与许多共生体建立联系而没有强制执行时,无论是突变还是移民,而是随机切换都不会使合作共生体扩散。利用共生体转换促进进化的例子包括寄生着大量胞内内生共生体的大型纤毛虫。这个简单的模型和规则将为理解具有正向适应性反馈且没有强制机制的微生物-微生物互利共生的进化提供一个基础。
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来源期刊
Theoretical Population Biology
Theoretical Population Biology 生物-进化生物学
CiteScore
2.50
自引率
14.30%
发文量
43
审稿时长
6-12 weeks
期刊介绍: An interdisciplinary journal, Theoretical Population Biology presents articles on theoretical aspects of the biology of populations, particularly in the areas of demography, ecology, epidemiology, evolution, and genetics. Emphasis is on the development of mathematical theory and models that enhance the understanding of biological phenomena. Articles highlight the motivation and significance of the work for advancing progress in biology, relying on a substantial mathematical effort to obtain biological insight. The journal also presents empirical results and computational and statistical methods directly impinging on theoretical problems in population biology.
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An almost infinite sites model A simple model and rules for the evolution of microbial mutualistic symbiosis with positive fitness feedbacks Sharp habitat shifts, evolutionary tipping points and rescue: Quantifying the perilous path of a specialist species towards a refugium in a changing environment Editorial Board Joint identity among loci under mutation and regular inbreeding
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