Garamszegi László Zsolt
Department of Evolutionary Ecology, Estación Biológica de Doñana-CSIC, c/Americo Vespucio, s/n, 41092, Sevilla, Spain.
Malar J. 2009 May 22;8:110. doi: 10.1186/1475-2875-8-110.
The evolutionary history of many parasites is dependent on the evolution of their hosts, leading to an association between host and parasite phylogenies. However, frequent host switches across broad phylogenetic distances may weaken this close evolutionary link, especially when vectors are involved in parasites transmission, as is the case for malaria pathogens. Several studies suggested that the evolution of the primate-infective malaria lineages may be constrained by the phylogenetic relationships of their hosts, and that lateral switches between distantly related hosts may have been occurred. However, no systematic analysis has been quantified the degree of phylogenetic association between primates and their malaria parasites.
Here phylogenetic approaches have been used to discriminate statistically between events due to co-divergence, duplication, extinction and host switches that can potentially cause historical association between Plasmodium parasites and their primate hosts. A Bayesian reconstruction of parasite phylogeny based on genetic information for six genes served as basis for the analyses, which could account for uncertainties about the evolutionary hypotheses of malaria parasites.
Related lineages of primate-infective Plasmodium tend to infect hosts within the same taxonomic family. Different analyses testing for congruence between host and parasite phylogenies unanimously revealed a significant association between the corresponding evolutionary trees. The most important factor that resulted in this association was host switching, but depending on the parasite phylogeny considered, co-speciation and duplication may have also played some additional role. Sorting seemed to be a relatively infrequent event, and can occur only under extreme co-evolutionary scenarios. The concordance between host and parasite phylogenies is heterogeneous: while the evolution of some malaria pathogens is strongly dependent on the phylogenetic history of their primate hosts, the congruent evolution is less emphasized for other parasite lineages (e.g. for human malaria parasites). Estimation of ancestral states of host use along the phylogenetic tree of parasites revealed that lateral transfers across distantly related hosts were likely to occur in several cases. Parasites cannot infect all available hosts, and they should preferentially infect hosts that provide a similar environment for reproduction. Marginally significant evidence suggested that there might be a consistent variation within host ranges in terms of physiology.
The evolution of primate malarias is constrained by the phylogenetic associations of their hosts. Some parasites can preserve a great flexibility to infect hosts across a large phylogenetic distance, thus host switching can be an important factor in mediating host ranges observed in nature. Due to this inherent flexibility and the potential exposure to various vectors, the emergence of new malaria disease in primates including humans cannot be predicted from the phylogeny of parasites.
许多寄生虫的进化史依赖于其宿主的进化，导致宿主与寄生虫系统发育之间存在关联。然而，跨越广泛系统发育距离的频繁宿主转换可能会削弱这种紧密的进化联系，特别是当媒介参与寄生虫传播时，如疟疾病原体的情况。几项研究表明，感染灵长类动物的疟原虫谱系的进化可能受到其宿主系统发育关系的限制，并且可能发生了远缘宿主之间的横向转换。然而，尚未有系统分析量化灵长类动物与其疟原虫之间的系统发育关联程度。
在这里，系统发育方法已被用于从统计学上区分可能导致疟原虫与其灵长类宿主之间历史关联的共分歧、重复、灭绝和宿主转换事件。基于六个基因的遗传信息对寄生虫系统发育进行贝叶斯重建，作为分析的基础，这可以解释疟原虫进化假说的不确定性。
感染灵长类动物的疟原虫相关谱系倾向于感染同一分类科内的宿主。对宿主和寄生虫系统发育一致性的不同分析一致揭示了相应进化树之间的显著关联。导致这种关联的最重要因素是宿主转换，但根据所考虑的寄生虫系统发育，共物种形成和重复也可能起到了一些额外作用。分类似乎是一个相对罕见的事件，并且仅在极端的协同进化情况下才会发生。宿主和寄生虫系统发育之间的一致性是异质的：虽然一些疟疾病原体的进化强烈依赖于其灵长类宿主的系统发育历史，但其他寄生虫谱系（例如人类疟原虫）的一致进化则不太明显。沿着寄生虫系统发育树估计宿主使用的祖先状态表明，在几种情况下可能发生了远缘宿主之间的横向转移。寄生虫不能感染所有可用宿主，它们应该优先感染为繁殖提供相似环境的宿主。微弱的证据表明，宿主范围内在生理方面可能存在一致的差异。
灵长类疟疾的进化受到其宿主系统发育关联的限制。一些寄生虫可以保持很大的灵活性来感染跨越广泛系统发育距离的宿主，因此宿主转换可能是介导自然界中观察到的宿主范围的一个重要因素。由于这种固有的灵活性以及可能接触各种媒介，包括人类在内的灵长类动物中新疟疾病的出现无法从寄生虫的系统发育中预测。
