The genetic basis of host resistance / susceptibility to parasite infection in a wild vertebrate population: a pilot study.

所有自然种群的动物都感染了病原体和寄生虫：这是正常的状态。由于这种寄生虫非常常见，它们是自然种群中的一支重要力量。面对寄生虫，动物并不被动--它们会产生免疫反应，试图保护自己。但是，我们对寄生虫感染在大多数野生种群中的行为知之甚少。我们也并不真正了解一些动物是如何以及为什么会有严重的感染，而另一些动物则几乎没有感染。我们建议在回答这些问题方面迈出第一步。为了做到这一点，我们将研究一群野生的青蛙(非洲爪蛙)，这种青蛙通常被一种蠕虫(异种原生毛虫)感染在它的膀胱里。我们使用的是对这种青蛙野生种群长达25年的研究结果，许多动物一生都在跟踪研究这种青蛙。重要的是，对于这些动物，我们知道它们有多少虫子。这些结果已经告诉我们，这些青蛙可以产生良好的免疫反应，使它们不受蠕虫的侵袭。但是，有一些动物总是被蠕虫感染，有些人偶尔会被感染。因此，不同的个体在攻击这些蠕虫方面的擅长程度各不相同。我们认为，造成动物之间这些差异的原因是它们所拥有的基因控制着它们的免疫系统如何工作。我们将通过比较不同动物的这些基因，特别是比较从未感染过蠕虫的动物和总是感染蠕虫的动物，来验证这一点是否正确。我们对此感兴趣的更大原因是为了了解为什么不同的个体动物在它们所患的不同种类的感染(例如病毒、细菌、真菌、蠕虫)方面存在差异。通过发现这一点，我们就可以开始研究现有的感染(或未来的新感染)可能会如何影响野生种群。这一点尤其重要，因为地球的气候正在变化，因为这使动物暴露在它们以前从未见过的感染中。目前两栖动物感染壶菌可能就是一个例子。

All natural populations of animals are infected with pathogens and parasites: this is the 'normal' state-of-affairs. Because such parasites are so common, they are an important force in natural populations. Animals are not passive in the face of parasites - they generate immune responses to try and protect themselves. But, we know rather little about how parasite infections behave in most wild populations. We also do not really understand how and why some animals have heavy infections, while others are hardly infected at all. We are proposing to take a first step in answering these questions. To do this we will study a wild population of frogs (Xenopus laevis) that is commonly infected by a worm (Protopolystoma xenopodis) in its bladder. We are using the results of an approximately 25 year-long study of a wild population of this frog, for which many animals have been followed throughout their lives. Importantly, for these animals we know how many worms they have had. These results have already told us that these frogs can make good immune responses that keep them free of worms. But, there are a number of animals who are always infected with worms, and some who occasionally become infected. So, different individuals vary in how good they are at attacking these worms. We think that what is causing these differences between animals is the genes they have that control how their immune system works. We are going to see if this is correct by comparing these genes in different animals, particularly comparing animals who never have worm infections with animals that always have worm infections. The bigger reason why we are interested in doing this is to understand why different individual animals vary in what different sorts of infections (e.g. virus, bacteria, fungus, worms) they have. By discovering this, we can then begin to work out how existing infections (or new infections in the future) might affect wild populations. This is especially important as the planet's climate is changing, because this is exposing animals to infections they have not seen before. The current infection of amphibians with chytrid fungus might be an example of this already.