Immunity at the population level: understanding the effects of environmental change

环境变化的一个特别难以预测的后果是传染病对不同气候的反应方式。这不仅对人很重要，而且对大多数动物和植物也很重要，因为它们在自然和人工管理的生态系统中经常成为疾病的受害者。如果我们想了解环境变化对疾病的影响，我们需要知道免疫系统在环境变化时是如何变化的，特别是当我们考虑变温动物（冷血生物）的疾病时：这些疾病在很多方面都受到温度等环境变量的强烈影响，包括它们对免疫力的投入程度。了解冷血动物的免疫力如何应对气候变化是很重要的，原因有很多。绝大多数动物都是变温动物，新的传染病对生态系统造成破坏和生物多样性丧失的可能性很大。有害动物，或者我们想要保护的稀有动物，可能会或多或少地受到疾病的影响，因此数量会增加或减少，从人类的角度来看，携带疟疾等疾病的昆虫的免疫反应可以决定它们是否能够携带这些疾病并将它们传播给人类：例如，蚊子的免疫系统会对抗蚊子携带的任何疟疾寄生虫。先前对变温动物免疫系统对环境的反应的研究表明，情况很复杂。如果进行一项实验室实验来衡量（例如）可获得的食物质量变化的影响，这肯定会告诉我们，如果食物可获得性发生变化，免疫力可能会如何变化，但这些信息是否有用是值得怀疑的：我们最近发现，免疫力对食物质量、温度或人口拥挤程度的反应方式本身取决于其他变量：例如，温度升高会导致免疫力的增强或减弱，这取决于动物的拥挤程度。当环境发生变化时，不可避免地会有不止一个这样的因素同时发生变化。例如，温度升高将导致降雨的变化和许多动物种类的丰富程度的变化，这意味着食物的数量和拥挤程度将随着温度的变化而变化。事实上，这些环境因素之间的相互作用使得预测变温免疫在现实世界系统中可能发生的变化基本上是不可能的：你需要知道系统的很多细节（温度、食物供应、湿度、人口密度等），你永远无法做出有用的预测。拟议中的研究将通过监测实验实验室生态系统中一个模型变温动物物种（一种被称为interpunctella的飞蛾）的免疫投资来回避这个问题，该生态系统将被保持在三种温度中的一种，并提供两种不同质量的食物。这些生态系统将运行大约20代飞蛾，我们将在此期间监测昆虫的免疫反应和它们抵抗细菌感染的能力。这种方法将告诉我们，在这些简单的实验室生态系统中，这些动物的免疫力是如何随着环境变化而变化的，而不需要测量系统的每一个细节（尽管我们将测量一些重要的细节，如人口密度）。我们还将测量蛾子是否在此期间进化，这是动物可能减轻环境变化影响的潜在重要方式。这项研究的结果将为我们提供非常详细的数据集，不仅告诉我们这些动物的免疫力和抗病能力是如何随着环境的变化而变化的，而且还告诉我们它们对环境变化的反应有多快。

One consequence of environmental change that is especially hard to predict is the way that infectious diseases will respond to a different climate. This is important not only for people but also for most animals and plants which are frequently victims of disease in both natural and managed ecosystems. If we want to understand the effects of environmental change on disease we need to know how immune systems change when the environment changes, especially when we are thinking about diseases of ectotherms (cold-blooded organisms): these are strongly affected by environmental variables like temperature in many ways, including how much they invest in immunity. Knowing about how immunity in cold-blooded animals will respond to climate change is important for many reasons. The vast majority of animals are ectotherms and the potential for disruption of ecosystems and loss of biodiversity from new infectious diseases is huge. Pest animals, or rare animals that we want to conserve, might become more or less affected by disease and therefore increase or decrease in number, and from a human point of view the immune responses of insects that carry diseases such as malaria can determine whether they are able to carry these diseases and transmit them to people: the immune systems of mosquitos, for example, act against any malaria parasites that the mosquito is carrying.Previous research into how ectotherm immunity reacts to the environment has shown that the picture is complicated. If carry out a lab experiment to measure the effect of changing (for example) the quality of food available, this will certainly tell us something about how immunity might change if food availability changes, but whether this information will be useful is questionable: what we have recently found is that the way that immunity responds to food quality, or temperature, or how crowded the population is, itself depends on other variables: increasing the temperature, for example, can lead to either increases or decreases in immunity depending on how crowded the animals are. When the environment changes it is inevitable that more than one such factor will change at the same time. Increasing temperature, for example, will lead to changes in rainfall and changes in the abundance of many animal species, meaning that the amount of food available and the degree of crowding will change as well as the temperature. In fact, the web of interactions between these environmental factors makes it essentially impossible to predict how ectotherm immunity is likely to change in real-world systems: you'd need to know so many details about the system (temperature, food availability, humidity, population density, etc.) that you'd never be able to make useful predictions.The proposed research will sidestep this problem by monitoring immune investment in a model ectotherm species (a moth called Plodia interpunctella) in experimental laboratory ecosystems that will be kept at one of three temperatures and provided with two different qualities of food. These ecosystems will be run for around twenty generations of the moth, and we will monitor the insects' immune responses and their ability to fight off bacterial infection throughout this period. This approach will tell us how immunity changes in these animals in these simple laboratory ecosystems as a consequence of environmental change without the need to measure every single detail of the system (although we will measure some important details like population density). We will also measure whether the moths evolve during this period, which is a potentially important way that animals might mitigate the effects of environmental change. The results of this research will give us a very detailed data set telling us not only how immunity and disease resistance in these animals changes with the environment, but also how fast they evolve in response to changes in the environment.