Specificity in parasites with multiple hosts: The view from the hosts' perspective

IF 0.2 Q4 EVOLUTIONARY BIOLOGY
G. Lozano
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引用次数: 1

Abstract

Reminiscent of Dawkins’ analogy using the Necker cube (Dawkins 1983), Forbes and Mlynarek (2014) offer us a different perspective of multi-host parasite systems. Forbes and Mlynarek point out that, traditionally, multi-host parasite systems have been mostly viewed from the perspective of the parasite. Parasites have shorter lifespans and hence, supposedly have the upper hand in the antagonistic coevolutionary race between parasites and host. It is logical to study the problem from the perspective of the party that is more likely to be better adapted. However, Forbes and Mlynarek suggest it is perhaps time to view the problem from the perspective of the hosts, and offer a hypothesis based on the degree of gene flow between host populations affected or unaffected by a given parasite. Forbes and Mlynarek’s ‘coevolutionary release hypothesis’ argues that when some host populations are not exposed to the parasite, gene flow from the unaffected host population hinders the affected host population’s ability to evolve resistance to the parasite. The hypothesis is sound, intuitive, and perhaps long overdue, yet surprisingly, Forbes and Mlynarek are tentative with their predictions, and choose not to fully explore the implications of their idea. They limit their predictions and discussion to the differences in parasite recognition and immunity among host populations. However, the process of parasite resistance is multifaceted and consists of several other layers of protection besides physiological or immunological adaptations. Here, I shall briefly speculate on how the coevolutionary release hypothesis can affect several other related areas, and I shall explore specific predictions and implications of examining multi-host systems from the hosts’ perspective. Behaviour is the first layer of protection against parasitism. Anti-parasitic behaviours are wide-ranging, and include, for example, avoiding infected individuals, simple preening and grooming, avoiding parasite-laden areas or food items, and even self-medication (Hart 1990, Villalba and Provenza 2009, Moore et al. 2013). Many of these behavioural defenses against parasites are learned, and many others are innate. The coevolutionary release hypothesis makes clear predictions about the degree and effectiveness of parasite-avoiding and parasite-defensive behaviours among host populations. The hypothesis predicts that the most effective parasiteprotection behaviours should evolve only in closed populations in which all potential hosts are exposed to the parasite, rather than in open populations. In contrast, the hypothesis makes no predictions about learned defenses—whether or not the host population is open or closed. For at least 30 years now, parasites have featured prominently in the study of sexual selection (Andersson 1994). There is no need here for an extensive review of the main hypotheses, but suffice it to say that, via various mechanisms, parasite resistance is thought to be indicated by ornamental colours and behaviours, which are hence important in mate selection. Populations differ in the degree to which they express sexual ornaments and these differences have been attributed to predation, parasite prevalence, condition, and other factors (e.g., Hill 1993, Baird et al. 1997, Magurran 1998). Forbes and Mlynarek add another possible cause for differences in the expression of sexual ornaments, in this case, among closely related species. The hypothesis predicts that closed populations—those not connected to populations not exposed to a given parasite—should develop the strongest resistance, and by extension, should have the most developed sexual ornaments. The relationship between ornaments and resistance can come about via several mechanisms, so if the main prediction is confirmed, several other research avenues become available.
多宿主寄生虫的特异性:从宿主的角度看
Forbes和Mlynarek(2014)让人想起Dawkins使用Necker立方体的类比(Dawkins 1983),为我们提供了多宿主寄生虫系统的不同视角。Forbes和Mlynarek指出,传统上,多宿主寄生虫系统大多是从寄生虫的角度来看待的。寄生物的寿命较短,因此在寄生物和寄主之间的共同进化竞争中占据上风。从更有可能更好适应的政党的角度来研究这个问题是合乎逻辑的。然而,Forbes和Mlynarek认为,现在也许是时候从宿主的角度来看待这个问题,并根据受特定寄生虫影响或未受影响的宿主种群之间的基因流动程度提出一个假设。Forbes和Mlynarek的“共同进化释放假说”认为,当一些宿主种群没有暴露于寄生虫时,来自未受影响宿主种群的基因流阻碍了受影响宿主种群进化出对寄生虫的抗性的能力。这个假设是合理的,直观的,也许早该出现了,但令人惊讶的是,福布斯和姆林纳莱克对他们的预测是试探性的,并选择不充分探索他们的想法的含义。他们将他们的预测和讨论限制在寄主群体对寄生虫的识别和免疫的差异上。然而,寄生虫抗性的过程是多方面的,除了生理或免疫适应外,还包括其他几层保护。在这里,我将简要地推测共同进化释放假说如何影响其他几个相关领域,并且我将从宿主的角度探讨检查多宿主系统的具体预测和含义。行为是防止寄生的第一层保护。抗寄生行为范围广泛,包括,例如,避开受感染的个体,简单的梳理和修饰,避免寄生虫密集的地区或食物,甚至自我用药(Hart 1990, Villalba和Provenza 2009, Moore等人2013)。这些针对寄生虫的行为防御有许多是后天习得的,还有许多是天生的。共同进化释放假说对宿主种群中躲避和防御寄生虫行为的程度和有效性做出了明确的预测。该假说预测,最有效的寄生虫保护行为应该只在所有潜在宿主都暴露于寄生虫的封闭种群中进化,而不是在开放种群中进化。相比之下,该假说没有对习得性防御做出预测——宿主群体是开放的还是封闭的。至少30年来,寄生虫在性选择研究中占有重要地位(Andersson 1994)。这里不需要对主要假设进行广泛的回顾,但足以说明,通过各种机制,寄生虫的抗性被认为是由装饰性的颜色和行为表明的,因此在配偶选择中很重要。种群表达性装饰的程度不同,这些差异归因于捕食、寄生虫流行、环境和其他因素(例如,Hill 1993, Baird et al. 1997, Magurran 1998)。Forbes和Mlynarek补充了另一种可能的原因,在这种情况下,在密切相关的物种中,性装饰的表达存在差异。该假说预测,封闭的种群——那些与没有接触过特定寄生虫的种群没有联系的种群——应该会产生最强的抵抗力,并由此推而广之,应该具有最发达的性装饰。装饰物和抵抗力之间的关系可以通过几种机制来实现,所以如果主要的预测得到证实,其他一些研究途径就可以使用。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Ideas in Ecology and Evolution
Ideas in Ecology and Evolution EVOLUTIONARY BIOLOGY-
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