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

环境变化的一个后果特别难以预测，那就是传染病对不同气候的反应方式。这不仅对人很重要，而且对大多数动植物也很重要，因为它们经常是自然生态系统和管理生态系统中疾病的受害者。如果我们想要了解环境变化对疾病的影响，我们需要知道当环境变化时免疫系统是如何变化的，特别是当我们考虑外温(冷血生物体)的疾病时：这些疾病在许多方面都受到温度等环境变量的强烈影响，包括它们在免疫方面的投资有多大。了解冷血动物的免疫力如何应对气候变化具有重要意义，原因有很多。绝大多数动物是超温动物，新的传染病破坏生态系统和丧失生物多样性的可能性是巨大的。害虫动物，或我们想要保护的珍稀动物，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其传播给人类：例如，蚊子的免疫系统可以对抗蚊子携带的任何疟疾寄生虫。以前关于外温免疫如何对环境做出反应的研究表明，情况是复杂的。如果进行实验室实验来衡量改变(例如)食物质量的效果，这肯定会告诉我们，如果食物可获得性发生变化，免疫力可能会发生什么变化，但这个信息是否有用还有待商榷：我们最近发现，免疫力对食物质量或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，提高温度可能会导致免疫力的增加或降低，具体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，气温上升将导致降雨量的变化和许多动物物种丰度的变化，这意味着可获得的食物量和拥挤程度将随着温度的变化而变化。事实上，这些环境因素之间相互作用的网络使得预测外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：你需要知道关于该系统的如此多的细节(温度、食物可获得性、湿度、人口密度等)。你永远无法做出有用的预测。这项拟议的研究将通过监测实验实验室生态系统中一种模式外温虫物种(一种名为Plodia inter杂点蛾)的免疫投资来避开这个问题，该物种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代蛾，我们将监测昆虫的免疫反应和它们在整个期间抵御细菌感染的能力。这种方法将告诉我们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，如种群密度)。我们还将测量飞蛾是否在这段时间内进化，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一个非常详细的数据集，告诉我们这些动物的免疫力和抗病能力如何随着环境的变化而变化，以及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.