Resolving the conflict: The ecology and evolution of horizontal versus vertical transmission strategies in a model insect-virus interaction

疾病感染整个自然界的动植物。它们可以通过直接接触或通过传染颗粒的转移，从感染者水平传播到易感人群。或者，这种疾病可以在成年生殖后垂直传播，当它从父母传给后代时。这种传播可能会持续许多代，受感染的动物似乎没有感染。这些被称为隐匿性疾病感染，因为病原体不会引起任何明显的症状。病原体环境中未受感染的宿主的数量是影响其传播效率的关键因素。当未感染宿主密度较高时，致死病原体的水平传播频繁发生，因为个体之间可以频繁接触。相反，当宿主密度低时，水平传播是有限的，或者根本不会发生。非致命性隐性感染的垂直传播可以发生，因为这种传播形式不依赖于感染者和非感染者之间的接触。由于致命性疾病的水平传播会杀死宿主，它显然会阻碍非致命性隐性感染的垂直传播，而非致命性隐蔽感染需要宿主生存和繁殖。解决传输模式之间的这种冲突是该提案的中心目标。我们将调查有利于不同传播方式的生态条件，并确定传播方式与病原菌毒力之间的联系。杆状病毒是感染节肢动物的病原体，特别是蝴蝶和飞蛾，这些病原体通过水平(和致命性)和垂直(非致命性)传播。致命的病毒暴发通常与高密度的森林害虫有关，但这些暴发通常是由于多年的低宿主密度和没有明显的病原体存在而分开的。在这些时候发生的事情是病原体生命周期的一个重要部分，人们对此知之甚少。我们的目的是验证这样一种观点，即主机密度是影响水平或垂直传播路线受青睐的关键因素。我们将通过监测长期实验室人群中致命性和隐蔽性感染的流行率来做到这一点，这些实验室人口的丰度模式明显不同。我们还将进行选择实验，以确定不同的传播途径如何影响宿主的生活史特征，如发育和繁殖力，以及病原体的生活史特征，如致病性和病毒生产。垂直传播的感染可能在那些稀有物种或那些密度变化很大的物种中特别重要，例如害虫和入侵物种。确定有利于一种或另一种传播方式的条件及其对宿主和疾病生态的影响至关重要。

Diseases infect plants and animals throughout the natural world. They may be horizontally transmitted from an infected individual to a susceptible individual either by direct contact or through the transfer of an infectious particle. Alternatively, the disease can be vertically transmitted following adult reproduction, when it is transferred from the parent to its offspring. This kind of transmission may continue for many generations with the infected animal appearing to be uninfected. These are called covert disease infections because the pathogen does not cause any visible symptoms. The abundance of uninfected hosts in a pathogen's environment is a key factor affecting how efficiently it is transmitted. When uninfected host density is high, horizontal transmission of lethal pathogens occurs frequently because individuals can come into contact with each other frequently. Conversely, when host densities are low, horizontal transmission is limited or may not occur at all. Vertical transmission of non-lethal covert infections can occur as this form of transmission does not depend on contact between infected and uninfected individuals. Since horizontal transmission of a lethal disease kills the host, it will clearly impede the vertical transmission of non-lethal covert infections, which need their host to survive and reproduce. Resolving this conflict between transmission modes is the central aim of the proposal. We will investigate the ecological conditions that favour different transmission modes and determine the link between transmission mode and pathogen virulence. Baculoviruses are pathogens that infect arthropods, especially butterflies and moths, and these pathogens are transmitted both horizontally (and lethally) and vertically (non-lethally). Lethal virus outbreaks are often associated with high densities of forest insect pests, but these outbreaks are typically separated by years of low host density and no obvious presence of pathogens. What happens at these times is an important part of the pathogen life cycle that is very poorly understood. We aim to test the idea that host density is a key factor affecting whether horizontal or vertical transmission routes are favoured. We will do this by monitoring the prevalence of lethal and covert infections in long term laboratory populations that differ markedly in patterns of abundance. We will also carry out selection experiments where we determine how the different transmission routes affect the life history traits of the host, such as development and fecundity, and of the pathogen, such as pathogenicity and virus production. Vertically transmitted infections are likely to be especially important in those species that are rare, or those species that have highly variable densities, such as pests and invasive species. Identifying the conditions that favour one or other transmission mode and their impact on both host and disease ecology is crucial.