King Kayla C, Bonsall Michael B
Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK.
BMC Evol Biol. 2017 Aug 14;17(1):190. doi: 10.1186/s12862-017-1030-z.
Animal and plant species can harbour microbes that provide them with protection against enemies. These beneficial microbes can be a significant component of host defence that complement or replaces a repertoire of immunity, but they can also be costly. Given their impact on host and parasite fitness, defensive microbes have the potential to influence host-parasite interactions on an evolutionary timescale.
Using a phenotypic framework, we explore the evolutionary and coevolutionary dynamics of a host-parasite interaction in the presence of defensive microbes. We show that costs of host-defensive microbe systems are critical in determining whether a defensive microbe based system or an immune system provides better host protection investment. Partitioning the coevolutionary dynamics yields testable predictions. The density of defensive microbes influences the strength of selection resulting from host - defensive microbe - parasite coevolutionary interactions. We find that they lessen the negative effects of infection on hosts and reduce infectivity by directly competing with parasites.
Defensive microbes might thus play a central role in host-parasite interactions, by outright replacing host-based defences, engaging in within-host competition with parasites, and ultimately driving tripartite coevolutionary dynamics.
动植物物种可能携带能为它们抵御天敌的微生物。这些有益微生物可能是宿主防御的重要组成部分，可补充或替代免疫机制，但它们也可能代价高昂。鉴于其对宿主和寄生虫适应性的影响，防御性微生物有可能在进化时间尺度上影响宿主 - 寄生虫的相互作用。
我们使用一个表型框架，探索了在存在防御性微生物的情况下宿主 - 寄生虫相互作用的进化和协同进化动态。我们表明，宿主防御性微生物系统的成本对于确定基于防御性微生物的系统还是免疫系统能提供更好的宿主保护投资至关重要。对协同进化动态进行划分可得出可检验的预测。防御性微生物的密度会影响宿主 - 防御性微生物 - 寄生虫协同进化相互作用所产生的选择强度。我们发现它们通过直接与寄生虫竞争来减轻感染对宿主的负面影响并降低感染力。
因此，防御性微生物可能在宿主 - 寄生虫相互作用中发挥核心作用，通过直接替代基于宿主的防御、与寄生虫进行宿主体内竞争，并最终推动三方协同进化动态。
