Host dispersal, individual variation and spatial heterogeneity in avian malaria

了解个体如何变化在进化生态学中尤为重要，因为这使我们能够了解个体如何对其环境做出反应。寄生虫占大多数物种，因此研究寄主和寄生虫之间的相互作用是了解野生种群的重要组成部分。尽管如此，很少有这样的研究在足够大的规模上进行，以提高我们对野生宿主-寄生虫相互作用的认识。宿主对寄生虫的感染在空间上有显著差异，即使在我国山雀种群中发生禽疟疾的地方尺度上也是如此。宿主带着它们的寄生虫走到哪里，所以宿主的传播是理解疾病空间异质性的一个重要因素。野生种群中寄生虫感染的风险因空间而异，通常是由于寄生虫感染阶段的丰度不同。这可能是由于环境条件的变化，如温度和湿度，或固有的空间过程，如疾病聚集。一个地点是否由于当地环境或受感染的人搬到那里而有高水平的疾病感染？拟议中的项目将研究牛津附近威瑟姆森林的大山雀和蓝山雀的长期种群。禽疟是由蚊子传播的，威瑟姆有30%的繁殖蓝山雀感染了禽疟。我们庞大的巢箱种群意味着大多数繁殖的鸟类在雏鸟时都被单独圈起来，这样我们就可以追踪它们的活动；我们可以在一个有用的地理范围内对大约500只成年蓝山雀和大山雀进行取样，以检查当地环境和宿主扩散对禽疟疾感染分布的影响。最近用于预测疾病分布和传播的统计模型考虑了这一空间维度，与现实生活中的流行病（如2001年的口蹄疫）的模式越来越吻合。有趣的是，在我们的研究种群中，禽疟寄生虫分为两个种群，每个种群都有不同的空间分布。利用基于dna的疟疾诊断、利用地理信息系统精确绘制空间位置、利用卫星图像对栖息地变化进行环境测量以及利用微型数据记录仪对小气候进行测量等方面的发展，意味着我们可以自信地解决直到最近还在生态学中令人生畏的逻辑问题。我们有三个目标：1。了解禽疟感染个体差异的原因。感染在多大程度上取决于出生条件、产妇状况、年龄或遗传因素？我们将结合现有的山雀禽疟疾长期数据，辅以本项目收集的数据，以及大规模的野外实验，在不同的巢穴之间切换鸟蛋。2. 确定观察到的两种疟疾物种的空间分布在多大程度上是由宿主驱动的过程造成的，特别是宿主的扩散。本研究将研究不同分布类型鸟类（包括迁入鸟类和留居鸟类）间禽疟感染的空间特征，并通过在林地间移动鸟类来控制鸟类的传播。3. 最后，我们将采用数学建模方法来检查宿主扩散、母体免疫和疟疾感染风险在产生我们在研究人群中看到的疾病空间模式中的相对作用。这些模型将集中在我们之前的工作中确定的重要影响上，产生新的可测试的假设，并导致进一步的经验和建模工作。这三种方法是由于对山雀种群的大量和充分研究而成为可能的，并将解决野生鸟类种群中禽疟疾的基本生态学问题，同时增加我们对疾病的更广泛了解。

Understanding how individuals vary is particularly important in evolutionary ecology, as this allows us to understand how individuals might respond to their environment. Parasites make up the majority of species, so investigating the interactions between hosts and parasites is an important part of understanding wild populations. Despite this, few such studies have been undertaken at a large enough scale to improve our knowledge of host-parasite interactions in the wild. Host infection with parasites varies markedly in space, even at a local scale in the case of avian malaria in our tit population. Hosts take their parasites with them wherever they go, so the dispersal of hosts is an important factor in understanding the spatial heterogeneity of disease. The risk of parasite infection in wild populations varies in space, often due to variation in the abundance of infectious stages of the parasite. This can be due to variation in environmental conditions such as temperature and humidity, or inherent spatial processes such as disease clustering. Does a site have a high level of disease infection due to the local environment, or because infected individuals have moved there? The proposed project will study a long term population of great tits and blue tits at Wytham Woods, near Oxford. Avian malaria is transmitted by mosquitoes, and infects 30% of breeding blue tits at Wytham. Our large nestbox population means that most breeding birds are individually ringed as chicks so we can track their movements; we can sample around 500 adults of both blue tits and great tits over a useful geographical scale to examine the influence of local environment and host dispersal on the distribution of avian malaria infection. Recent statistical models to predict the distribution and spread of disease that take account of this spatial dimension provide an increasingly good fit to the patterns seen in real life epidemics, such as the 2001 foot and mouth epidemic. Interestingly, the avian malaria parasites in our study population fall into two species groups that each has a different spatial distribution. Developments in the use of DNA-based malaria diagnosis, the use of Geographical Information Sytems to accurately map spatial locations and environmental measurements of habitat variation using satellite imagery and microclimate using miniature data loggers mean that we can confidently approach what were, until recently, logistically daunting questions in ecology. We have three objectives: 1. To understand the causes of individual variation in infection with avian malaria. To what extent is infection determined by natal conditions, maternal status, age or inherited factors? We will use a combination of existing long-term data on avian malaria in tits complemented by data collected during this project, and a large scale field experiment to switch clutches of eggs between nests. 2. To determine the extent to which the observed spatial distribution of the two malaria species results from host-driven processes, particularly host dispersal. We will examine the spatial characteristics of avian malaria infection between classes of birds with different dispersal, both residents and immigrants to the population, and conduct an experiment to manipulate dispersal by moving birds between woodlands. 3. Finally, we will employ a mathematical modelling approach to examine the relative roles if host dispersal, maternal immunity and the risk of malaria infection in generating the spatial patterns of disease we see in our study population. These models will concentrate on the important effects identified by our preceding work, generating new testable hypotheses and leading to further empirical and modelling work. These three approaches are made possible by the large and well studied population of tits, and will address the fundamental ecology of avian malaria in a wild bird population, while increasing our wider understanding of disease.