An epidemiological study of haemosporidian infections in blue tits (Cyanistes caeruleus) and great tits (Parus major) along an elevation gradient
Thesis or dissertation
University of Exeter
Climate characteristics are expected to play a decisive role in determining vector-mediated disease epidemiology (Mills et al. 2010). However, clear predictions on the responses of parasites to climatic changes are lacking (Seghal, 2015). Here I investigate differences in prevalence, diversity and costs associated with haemosporidian infections in breeding populations of blue tits (Cyanistes caeruleus), and great tits (Parus major) situated along a significant altitude gradient (430m-1530m). Avian haemosporidian parasites were detected in 92.7% blue tits and 91.5% great tits, representing 44 unique mitochondrial haplotypes. In total we recovered 11 verified Leucocytozoon parasite lineages, 3 Haemoproteus and 1 Plasmodium relictum. Mixed infections were reported in 17.7% blue tits and 21.3% great tits. While distribution of the detected parasite lineages differed between hosts and sites, we found no significant effect of altitude on infection prevalence, or parasite lineage richness. Furthermore, there was no detected effect of altitude on the cost of infection, measured either as individual body condition or reproductive success. Blue tits infected with Plasmodium lineages, and great tits infected with Haemoproteus lineages were significantly heavier than uninfected conspecifics or those carrying other infection types. Blue tits infected with either Haemoproteus or Leucocytozoon parasites exhibited significantly delayed hatching. The cost of infection on reproductive success was significant among birds carrying mixed infections only. Great tits infected with more than one parasite lineage showed significantly reduced hatching success, while blue tits carrying mixed infections had reduced fledging success. The results suggest the impacts of climatic differences on infections were either negligible, or that connectivity of vectors and hosts between sites prevented detection of any variation that occurred as a result of climate differences. The variation in haemosporidian parasite prevalence and diversity between sites and species is supportive of previous studies that suggest small-scale habitat heterogeneity influences vector community composition and individual host movements which may be important in determining host infection patterns (Sehgal, 2015, Perez-Rodriquez et al. 2013). Better detection of mixed parasite infections (van Rooyen et al. 2013) and further long-term sampling of natural populations, will help inform predictions of how vector-mediated diseases will respond to climate change (Martens et al. 1995, Garamszegi, 2011).
This thesis is presented in two chapters. Chapter 1 introduces a review of the current literature on avian haemosporidian parasites, and the factors that influence prevalence and distribution patterns within avian host communities. Current limitations to research on avian haemosporidia carried out to date are discussed, and future priorities to improve understanding and knowledge of the disease system recommended. The use of avian populations and their infecting haemosporidian parasites as a model system to predict climate change outcomes on vector-mediated diseases is described. This leads on to the second chapter, which describes a correlational study using molecular and reproductive data recorded from nest box populations of blue tits (Cyanistes caeruleus) and great tits (Parus major). The study assesses fitness costs to hosts associated with three genera of avian haemosporidian parasites (Leucocytozoon, Haemoproteus and Plasmodium) along a climatic gradient. This is used to assess likely implications of broader climate change shifts to this complex vector-mediated disease system.
Bonneaud, Dr Camille
MbyRes Biological Sciences