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Abstract：
Current research on the virulence evolution of Toxoplasma gondii is mainly conducted via experiments, and studies using mathematical models are still limited. Here, we constructed a complex cycle model of T. gondii in a multi-host system considering multiple transmission routes and cat-mouse interaction. Based on this model, we studied how the virulence of T. gondii evolves with the factors related to transmission routes and the regulation of infection on host behavior under an adaptive dynamics framework. The study shows that all factors that enhance the role of mice favored decreased virulence of T. gondii, except the decay rate of oocysts that led to different evolutionary trajectories under different vertical transmission. The same was true of the environmental infection rate of cats, whose effect was different under different vertical transmission. The effect of the regulation factor on the virulence evolution of T. gondii was the same as that of the inherent predation rate depending on its net effect on direct and vertical transmissions. The global sensitivity analysis on the evolutionary outcome suggests that changing the vertical infection rate and decay rate was most effective in regulating the virulence of T. gondii. Furthermore, the presence of coinfection would favor virulent T. gondii and make evolutionary bifurcation easy to occur. The results reveal that the virulence evolution of T. gondii had a compromise between adapting to different transmission routes and maintaining the cat-mouse interaction thereby leading to different evolutionary scenarios. This highlights the significance of evolutionary ecological feedback to evolution. In addition, the qualitative verification of T. gondii virulence evolution in different areas by the present framework will provide a new perspective for the study of evolution.
摘要：
目前对弓形虫毒力进化的研究主要是通过实验,使用数学模型的研究仍然有限。这里,我们在多宿主系统中构建了弓形虫的复杂周期模型，考虑了多种传播途径和猫鼠相互作用。基于这个模型,我们在适应性动力学框架下研究了弓形虫的毒力如何随着传播途径和感染对宿主行为的调节而演变。研究表明，所有增强小鼠作用的因素都有利于弓形虫的毒力降低，除了卵囊的衰减率导致不同的进化轨迹在不同的垂直传播下。猫的环境感染率也是如此，在不同的垂直传输下，其效果不同。调节因子对弓形虫毒力进化的影响与固有捕食率的影响相同，这取决于其对直接和垂直传播的净影响。对进化结果的全局敏感性分析表明，改变垂直感染率和腐烂率在调节弓形虫毒力方面最有效。此外，共感染的存在有利于毒力弓形虫，并使进化分叉容易发生。结果表明，弓形虫的毒力进化在适应不同的传播途径和维持猫鼠相互作用之间存在折衷，从而导致不同的进化情景。这凸显了进化生态反馈对进化的重要性。此外,本框架对不同地区弓形虫毒力进化的定性验证将为进化研究提供新的视角。
