Parasites: proxies for host genealogy and ecology?

Genetic information is used extensively to reconstruct the evolutionary and demographic history of organisms. Recently, it has been suggested that genetic information from some parasites can complement genetic data from their hosts. This approach relies upon the hypothesis that such parasites share a common history with their host. In some cases, parasites provide an additional source of information because parasite data can better reconstruct the common history. Here, we discuss which parasite traits are important in determining their usefulness for analysing host history. The key is the matching of the traits of the parasite (e.g. effective population size, generation time, mutation rate and level of host specificity) with the timescales (phylogenetic, phylogeographic and demographic) that are relevant to the issues of concern in host history.