School of Biological Sciences, University of Sydney, NSW 2006, Australia.
Ecology. 2010 Mar;91(3):872-81. doi: 10.1890/09-0530.1.
The process of rapid range expansion (as seen in many invasive species, and in taxa responding to climate change) may substantially disrupt host-parasite dynamics. Parasites and pathogens can have strong regulatory effects on their host population and, in doing so, exert selection pressure on host life history. We construct a simple individual-based model of host-parasite dynamics during range expansion. This model shows that the parasites and pathogens of a range-expanding host are likely to be absent from the host's invasion front, because stochastic events (serial founder events) in low-density frontal populations result in local extinctions or transmission failure of the parasite/pathogen and, hence, a preponderance of uninfected hosts in the invasion vanguard. This pattern is true for both density-dependent and density-independent transmission rates, although it is exacerbated in the case of density-dependent transmission because, in this case, transmission rates also decline on the front. Data from field surveys on the prevalence of lungworms (Rhabdias pseudosphaerocephala) in invasive cane toads (Bufo marinus) support these predictions, in showing that toads in newly invaded areas of tropical Australia lack the parasite, which only arrives 1-3 years after the toads themselves. The resultant "honeymoon phase" immediately post-invasion, when individuals in the invasion-front population are virtually pathogen-free, may lead to altered host population dynamics on the invasion front, causing, for example, high densities in invasion-front populations, followed by a decline in numbers as parasites and pathogens arrive and begin to reduce host viability. The honeymoon phase may ultimately impact the evolution of life-history investment strategies in both host and parasite on the invasion vanguard, as hosts are released from immune challenges and parasites continuously expand into a favorable and unoccupied niche.
快速分布范围扩张（在许多入侵物种以及对气候变化做出反应的类群中可见）的过程可能会极大地破坏宿主-寄生虫动态。寄生虫和病原体对宿主种群具有强大的调节作用，因此，它们对宿主的生活史施加选择压力。我们构建了一个在分布范围扩张期间宿主-寄生虫动态的简单个体基础模型。该模型表明，处于扩张中的宿主的寄生虫和病原体很可能不存在于宿主的入侵前沿，因为低密度前沿种群中的随机事件（系列创始事件）导致寄生虫/病原体的局部灭绝或传播失败，从而使未感染的宿主在入侵先锋中占优势。这种模式对于密度依赖和密度独立的传播率都是如此，尽管在密度依赖的传播情况下更为严重，因为在这种情况下，传播率也会在前沿下降。对入侵的热带澳大利亚地区肺蠕虫（Rhabdias pseudosphaerocephala）流行率的实地调查数据支持了这些预测，表明新入侵地区的蟾蜍缺乏寄生虫，而寄生虫仅在蟾蜍到达 1-3 年后才到达。入侵后立即出现的“蜜月期”，即在入侵前沿种群中的个体几乎没有病原体的情况下，可能导致入侵前沿的宿主种群动态发生变化，例如，入侵前沿种群的密度增加，然后随着寄生虫和病原体的到来并开始降低宿主的生存能力，数量下降。蜜月期可能最终影响入侵先锋中的宿主和寄生虫的生活史投资策略的进化，因为宿主摆脱了免疫挑战，寄生虫不断扩张到有利且未被占据的生态位。
