The evolutionary ecology of Leucocytozoon blood parasites of birds

Abstract

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.