Parasites can impose fitness effects on host populations: there may be seasonal and
geographic variation in the interaction as well as over a longer time scale, host-parasite
cospeciation. I investigate the Leucocytozoa parasites of birds as a model system to try
to understand the role of diversity of infection, dispersal and scale on the nature of the
coevolutionary process between the hosts and parasites.
Leucocytozoa had effects on the breeding success of a population of the blue tit,
Cyanistes caeruleus. Number of infections was important, and old birds infected with
mixed lineage infections raised broods of significantly lower quality than those infected
by a single lineage or uninfected birds. There was also evidence for individual lineage
effects. The parasites showed seasonal dynamics, and overall prevalence followed a
model previously proposed for the dynamics of avian malaria. Individual lineages
however, displayed different dynamics; this emphasises the importance of consideration
of lineage identity. These results may have consequences for the evolutionary dynamics
of this host-parasite interaction. The geographic context of the Leucocytozoa-bird
interaction was investigated, and little phylogeographic structuring was found in
parasite lineages across Europe. Contrary to predictions, the distribution of individual
lineages followed the abundance-occupancy relationship, suggestive of widespread
dispersal. At a larger phylogenetic scale I looked for evidence of host-parasite
cospeciation in this system. There was a strong signal of coevolution due to
cospeciation in 40% of the host-parasite associations. Migrant hosts harboured
significantly fewer cospeciating parasites than residents and partial migrants. The implications and potential applications of this type of cospeciation analysis are
discussed.
I conclude by suggesting that the bird-Leucocytozoon system is an excellent
model system for the study of host-parasite interactions, attaining high diversity and
prevalence in some cases. Furthermore, the role of diversity, mixed lineage infections
and dispersal are key to our understanding of the evolutionary dynamics of this system
