The influence of the host sex on parasitemia of parasite lineages belonging to Haemoproteus majoris in a natural bird community.

Immunological capability shows a sexual dimorphism in diverse animal species. Females are generally more immunocompetent than males, leading to the higher susceptibility of males to infection compared to females and thus greater infection-related pathology in males. These sex-differences in immunity remain understudied in birds. Here, we compared the percentage of parasitemia of three different parasite lineages belonging to the morphological species Haemoproteus majoris (namely, PARUS1, PHSIB1 and WW2) in terms of the sex of birds living in a natural community. We found that parasitemia (percentage of erythrocytes infected with parasites) of WW2 lineage, but not of the other two lineages of H. majoris, is higher in male birds compared to female birds. Similarly, we showed that the total parasitemia of these three H. majoris lineages is higher in male birds compared to female birds. Our study points out that male birds at the community level may be more susceptible to infection by certain parasites than female birds. We propose that sexual dimorphism in parasitemia of certain parasites in host birds might be more common than previously thought, similar to what is observed in other species, influencing host population dynamics in a sex-specific manner. Therefore, it can be speculated that infection by certain parasites might differentially affect male and female birds, possibly resulting in a bias in survival rates between sexes due to infections, in certain contexts.

Generalist haemosporidian parasites are better adapted to a subset of host species in a multiple host community.

Parasites that can infect multiple host species are considered to be host generalists with low host specificity. However, whether generalist parasites are better adapted to a subset of their host species remains unknown. To elucidate this possibility, we compared the variation in prevalence and infection intensity among host species of three generalist parasite lineages belonging to the morphological species Haemoproteus majoris, in a natural bird community in southern Sweden. Prevalence in each host species was confirmed by nested PCR and DNA sequencing, and infection intensities were quantified using lineage-specific real-time qPCR. For two of the three lineages, we detected positive correlations between prevalence and infection intensity, indicating that these generalist parasites are better adapted to a subset of host species, which may have been more frequently encountered during the evolution of the parasite; we refer to these as main host species. For both lineages, the main host species were more phylogenetically related than expected by chance as revealed by strong phylogenetic signal in prevalence among hosts. By comparing our results with previous records of these parasites, we found that the host range of a generalist parasite can vary among different communities and may partly be shaped by the presence of other parasites. Our study reveals that generalist parasites may be specialized on a subset of their host species and it highlights the importance of considering infection intensity and host phylogeny when determining the host specificity of a parasite.

Patterns of Haemoproteus majoris (Haemosporida, Haemoproteidae) megalomeront development.

Blood parasites of the genus Haemoproteus (Haemosporida, Haemoproteidae) are cosmopolitan and prevalent in birds. Numerous species and lineages of these pathogens have been identified. Some of the infections are lethal in avian hosts mainly due to damage of organs by tissue stages, which remain insufficiently investigated. Several closely related lineages of Haemoproteus majoris, a common parasite of passeriform birds, have been identified. One recent study described megalomeronts of unique morphology in the lineages hPHYBOR04 and hPARUS1 of H. majoris and suggested that the similar tissues stages might also be features in other phylogenetically closely related lineages of the same parasite species. This study aimed to test if (i) megalomeronts are present during the development of the lineage hPHSIB1 of H. majoris and if (ii) they are similar to the other investigated lineages of this species in regard of their morphology and location in organs. One adult wood warbler Phylloscopus sibilatrix, an Afrotropical migrant, naturally infected with H. majoris lineage hPHSIB1 was wild-caught after seasonal spring migration and screened using microscopic examination of blood films and histological sections of organs as well as using PCR-based testing. Bayesian phylogenetic analysis placed the lineages hPHSIB1, hPHYBOR04 and hPARUS1 in one, well-supported clade. Parasitaemia was high (6.5%) in the examined wood warbler, numerous megalomeronts were found in kidneys, and a few in the intestine. Megalomeronts of the lineage hPHSIB1 were morphologically hardly distinguishable from those of lineages hPHYBOR04 and hPARUS1; only negligible differences in the maturation stage of the cytomeres were seen. The kidneys were the main location site of the megalomeronts in all three lineages of this parasite species. This study shows that closely related lineages of H. majoris produce megalomeronts of similar morphology and predominant location in kidneys, while the normal function of this organ may be affected by the presence of numerous large megalomeronts. Megalomeronts of different avian Haemoproteus species are markedly variable in morphology and location, but phylogenetically closely related lineages possess cryptic megalomeronts. This finding suggests that phylogenies based on partial cytb gene could provide information for prediction of patterns of exo-erythrocytic development of closely related Haemoproteus parasites and are worthy of attention in planning haemosporidian parasite tissue stage research.

Persistence of avian haemosporidians in the wild: a case study to illustrate seasonal infection patterns in relation to host life stages.

Infection patterns of avian haemosporidians result from the evolution of their associations with hosts, and can be shaped by multiple biotic factors. However, at the level of parasite species, few studies have investigated the details of the temporal dynamics of infection patterns in wild bird communities. We hereby studied a wild bird community in southern Sweden to investigate two generalist parasites (cyt b lineages PARUS1 and WW2) of the morphological species Haemoproteus majoris in their main host species (tits and warblers, respectively) to look for seasonal (spring to autumn) and age class related variation in infection patterns. For both lineages, we detected a similar temporal pattern in prevalence and infection intensity, with peak levels during the main nesting season in adults and a few weeks later in juveniles. Infections in juveniles were detected as soon as they started to be caught by mist nets, implying that they became infected when still in the nest or during the first weeks post-fledging. The initially high intensities in juveniles were followed by a significant decrease during the hatching year, emphasising the importance of studying haemosporidian infections in nestlings and fledglings. Both prevalence and infection intensity in adults increased from spring to early summer, either due to spring relapses or new infections. Both prevalence and infection intensity declined in adults at the time when independent juveniles of the respective species started to appear, suggesting that the rate of parasite withdrawal from blood exceeded the rates of new infections gained and relapses of previous infections. Prevalence in both juveniles and adults approached zero towards the end of the summer.