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

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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.