Abstract
BackgroundOne of the major issues concerning disease ecology and conservation is knowledge of the factors that influence the distribution of parasites and consequently disease outbreaks. This study aimed to investigate avian haemosporidian composition and the distribution of these parasites in three altitudinally separated great tit (Parus major) populations in western Switzerland over a three-year period. The objectives were to determine the lineage diversity of parasites occuring across the study populations and to investigate whether altitudinal gradients govern the distribution of haemosporidian parasites by lineage.MethodsIn this study molecular approaches (PCR and sequencing) were used to detect avian blood parasites (Plasmodium sp., Haemoproteus sp. and Leucocytozoon sp.) in populations of adult great tits caught on their nests during three consecutive breeding seasons.ResultsHigh levels of parasite prevalence (88-96%) were found across all of the study populations with no significant altitude effect. Altitude did, however, govern the distribution of parasites belonging to different genera, with Plasmodium parasites being more prevalent at lower altitudes, Leucocytozoon parasites more at high altitude and Haemoproteus parasite prevalence increasing with altitude. A total of 27 haemosporidian parasite lineages were recorded across all study sites, with diversity showing a positive correlation to altitude. Parasites belonging to lineage SGS1 (P. relictum) and PARUS4 and PARUS19 (Leucocytozoon sp.) dominated lower altitudes. SW2 (P. polare) was the second most prevalent lineage of parasite detected overall and these parasites were responsible for 68% of infections at intermediate altitude, but were only documented at this one study site.ConclusionsAvian haemosporidian parasites are not homogeneously distributed across host populations, but differ by altitude. This difference is most probably brought about by environmental factors influencing vector prevalence and distribution. The high occurrence of co-infection by different genera of parasites might have pronounced effects on host fitness and should consequently be investigated more rigorously.
Highlights
One of the major issues concerning disease ecology and conservation is knowledge of the factors that influence the distribution of parasites and disease outbreaks
Avian haemosporidian parasites (Plasmodium sp., Haemoproteus sp. and Leucocytozoon sp.) have a worldwide distribution, and it is speculated that this wide distribution is due to a combination of high host mobility, migration, low parasite specificity and limited specificity in vector choice for hosts [1], thereby enabling the transmission of parasites belonging to numerous genera of Haemosporida
Mosquito populations have been monitored for several years in the three study populations and potential Plasmodium parasite vectors, such as Culex pipiens [7], are frequent in the low altitudinal site, less frequent at the mid altitudinal site and have never been captured at high altitude, where only one mosquito species feeding on mammals (Aedes sp.) has been encountered
Summary
One of the major issues concerning disease ecology and conservation is knowledge of the factors that influence the distribution of parasites and disease outbreaks. This study aimed to investigate avian haemosporidian composition and the distribution of these parasites in three altitudinally separated great tit (Parus major) populations in western Switzerland over a three-year period. The objectives were to determine the lineage diversity of parasites occuring across the study populations and to investigate whether altitudinal gradients govern the distribution of haemosporidian parasites by lineage. Avian haemosporidian parasites are represented by over 130 species (that are distinguishable by morphological characters) of the genus Haemoproteus, over 50 species of the genus Plasmodium and 35 species of the genus Leucocytozoon [1,3]. (Haemoproteus) parasites are vectored by hippoboscid flies (Hippoboscidae) [1] and are currently known to occur only in the Columbiformes [1], Pelecaniformes [5] and Charadriiformes [6]. Leucocytozoids, on the other hand, are transmitted by simuliid flies (Simuliidae) [1]
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