Dispersal in a patchy landscape reveals contrasting determinants of infection in a wild avian malaria system

Sympatry in a nightingale contact zone has no effect on host-specific blood parasite prevalence and lineage diversity

Parasites are a key driving force behind many ecological and evolutionary processes. Prevalence and diversity of parasites, as well as their effects on hosts, are not uniform across host species. As such, the potential parasite spillover between species can significantly influence outcomes of interspecific interactions. We screened two species of Luscinia nightingales for haemosporidian blood parasites (Plasmodium, Leucocytozoon and Haemoproteus) along an approximately 3000 km transect in Europe, incorporating areas of host distant allopatry, close allopatry and sympatry. We found significant differences in infection rates between the two host species, with common nightingales having much lower parasite prevalence than thrush nightingales (36.7% versus 83.8%). This disparity was mostly driven by Haemoproteus prevalence, which was significantly higher in thrush nightingales while common nightingales had a small, but significantly higher, Plasmodium prevalence. Furthermore, we found no effect of proximity to the contact zone on infection rate in either host species. Despite having lower infection prevalence, common nightingales were infected with a significantly higher diversity of parasite lineages than thrush nightingales, and lineage assemblages differed considerably between the two species, even in sympatry. This pattern was mostly driven by the large diversity of comparatively rare lineages, while the most abundant lineages were shared between the two host species. This suggests that, despite the close evolutionary relationships between the two nightingales, there are significant differences in parasite prevalence and diversity, regardless of the distance from the contact zone. This suggests that spillover of haemosporidian blood parasites is unlikely to contribute towards interspecific interactions in this system.

The drivers of avian-haemosporidian prevalence in tropical lowland forests of New Guinea in three dimensions

Haemosporidians are among the most common parasites of birds and often negatively impact host fitness. A multitude of biotic and abiotic factors influence these associations, but the magnitude of these factors can differ by spatial scales (i.e., local, regional and global). Consequently, to better understand global and regional drivers of avian-haemosporidian associations, it is key to investigate these associations at smaller (local) spatial scales. Thus, here, we explore the effect of abiotic variables (e.g., temperature, forest structure, and anthropogenic disturbances) on haemosporidian prevalence and host-parasite networks on a horizontal spatial scale, comparing four fragmented forests and five localities within a continuous forest in Papua New Guinea. Additionally, we investigate if prevalence and host-parasite networks differ between the canopy and the understory (vertical stratification) in one forest patch. We found that the majority of Haemosporidian infections were caused by the genus Haemoproteus and that avian-haemosporidian networks were more specialized in continuous forests. At the community level, only forest greenness was negatively associated with Haemoproteus infections, while the effects of abiotic variables on parasite prevalence differed between bird species. Haemoproteus prevalence levels were significantly higher in the canopy, and an opposite trend was observed for Plasmodium. This implies that birds experience distinct parasite pressures depending on the stratum they inhabit, likely driven by vector community differences. These three-dimensional spatial analyses of avian-haemosporidians at horizontal and vertical scales suggest that the effect of abiotic variables on haemosporidian infections are species specific, so that factors influencing community-level infections are primarily driven by host community composition.

Haemosporidian prevalence, parasitaemia and aggregation in relation to avian assemblage life history traits at different elevations

The transmission of vector-borne protozoa such as parasites of the Order Haemosporida is dependent on both biotic and abiotic factors such as host life history traits and environmental conditions. This study aimed to identify the variables that determine haemosporidian prevalence, parasitaemia and aggregation within the context of elevation and avian life history traits in Central Veracruz, Mexico. We sampled 607 birds from 88 species; we used microscopy and the mtDNA cytochrome b gene to detect parasites. We found an overall prevalence of 32.3%. Haemosporidian prevalence was 21.6% in tropical sub-deciduous forest (at sea level), 38% in tropical deciduous forest (265 m above sea level (asl)), 19.4% in montane cloud forest (1630 m asl), and 51.7% in pine-oak forest (2790 m asl). The prevalence of each parasite genus was strongly influenced by elevation (a proxy of habitat type). Plasmodium showed the highest prevalence at low elevation. Haemoproteus increased in prevalence with elevation. Leucocytozoon displayed the highest prevalence at the highest elevation (pine-oak forest). Haemoproteus spp. and Leucocytozoon spp. prevalences were higher in open cup than in closed nests. Haemoproteus prevalence and haemosporidian parasitaemia were lower in solitary birds than birds with pairing and gregarious behavior. Haemosporidian aggregation decreased with elevation, yielding the significantly lowest values at the pine-oak forest. Elevation distribution patterns of prevalence for each genus were similar to those previously reported in other geographical areas (e.g., South America, Europe).

Robust geographical determinants of infection prevalence and a contrasting latitudinal diversity gradient for haemosporidian parasites in Western Palearctic birds

Identifying robust environmental predictors of infection probability is central to forecasting and mitigating the ongoing impacts of climate change on vector-borne disease threats. We applied phylogenetic hierarchical models to a data set of 2,171 Western Palearctic individual birds from 47 species to determine how climate and landscape variation influence infection probability for three genera of haemosporidian blood parasites (Haemoproteus, Leucocytozoon, and Plasmodium). Our comparative models found compelling evidence that birds in areas with higher vegetation density (captured by the normalized difference vegetation index [NDVI]) had higher likelihoods of carrying parasite infection. Magnitudes of this relationship were remarkably similar across parasite genera considering that these parasites use different arthropod vectors and are widely presumed to be epidemiologically distinct. However, we also uncovered key differences among genera that highlighted complexities in their climate responses. In particular, prevalences of Haemoproteus and Plasmodium showed strong but contrasting relationships with winter temperatures, supporting mounting evidence that winter warming is a key environmental filter impacting the dynamics of host-parasite interactions. Parasite phylogenetic community diversities demonstrated a clear but contrasting latitudinal gradient, with Haemoproteus diversity increasing towards the equator and Leucocytozoon diversity increasing towards the poles. Haemoproteus diversity also increased in regions with higher vegetation density, supporting our evidence that summer vegetation density is important for structuring the distributions of these parasites. Ongoing variation in winter temperatures and vegetation characteristics will probably have far-reaching consequences for the transmission and spread of vector-borne diseases.

Environmental determinants of haemosporidian parasite prevalence in a declining population of Tree swallows

The prevalence of vector-borne parasites such as haemosporidian species is influenced by several environmental factors. While the negative effects of parasitism on hosts are well documented, these can also be amplified by interactions with environmental stressors, many of which are anthropogenic. Yet, we know little about the possible effects of anthropogenic perturbations on parasite prevalence. The goals of this study were to assess the prevalence and environmental determinants of haemosporidian parasites in a declining population of Tree swallows (Tachycineta bicolor) living in an agricultural landscape in southern Québec, Canada. Overall, a low prevalence and a moderate lineage diversity were identified in both adults and nestlings, confirming that transmission can occur during the breeding period. Anthropic areas, extensive cultures (hayfields and pastures) and forest cover within 500 km of nest boxes, as well as daily temperature fluctuations, were all related to infection by haemosporidian parasites. These findings suggest that anthropogenic alterations of landscape composition can modulate the prevalence of haemosporidian parasites in Tree swallows. Our results represent a baseline for future comparative studies assessing haemosporidian parasite prevalence in human-modified landscapes.

Testing Local Adaptation in a Natural Great Tit-Malaria System: An Experimental Approach

Finding out whether Plasmodium spp. are coevolving with their vertebrate hosts is of both theoretical and applied interest and can influence our understanding of the effects and dynamics of malaria infection. In this study, we tested for local adaptation as a signature of coevolution between malaria blood parasites, Plasmodium spp. and its host, the great tit, Parus major. We conducted a reciprocal transplant experiment of birds in the field, where we exposed birds from two populations to Plasmodium parasites. This experimental set-up also provided a unique opportunity to study the natural history of malaria infection in the wild and to assess the effects of primary malaria infection on juvenile birds. We present three main findings: i) there was no support for local adaptation; ii) there was a male-biased infection rate; iii) infection occurred towards the end of the summer and differed between sites. There were also site-specific effects of malaria infection on the hosts. Taken together, we present one of the few experimental studies of parasite-host local adaptation in a natural malaria system, and our results shed light on the effects of avian malaria infection in the wild.

Molecular and morphological characterization of Haemoproteus (Parahaemoproteus) ptilotis, a parasite infecting Australian honeyeaters (Meliphagidae), with remarks on prevalence and potential cryptic speciation

Avian Haemoproteus (Haemosporida) parasites occur in birds on all continents apart from Antarctica. Molecular screening techniques have uncovered previously unforeseen levels of Haemoproteus lineage diversity; however, fewer than 20% of genetic parasite lineages have been linked to morphological descriptions. The process of linking morphological descriptions to DNA barcodes for Haemoproteus spp. is important for the study of host-parasite interactions and the potential for cryptic speciation. Here, we describe cytochrome-b barcodes and morphological diagnostics for the identification of Haemoproteus (Parahaemoproteus) ptilotis, a systematically confusing parasite found in Australian honeyeaters (family Meliphagidae). We characterised infections from the original type host (Lichenostomus chrysops; Family Meliphagidae) as well as from four co-occurring meliphagid species in southeast Queensland, Australia, to investigate intraspecific variation in morphology and lineage identity. We recorded eight lineages that grouped into a well-supported monophyletic group, supporting the linkage of the described lineages to H. ptilotis. However, comparisons of diagnostics between the type host and co-occurring meliphagid hosts revealed high genetic diversity and variable morphology that could be indicative of cryptic speciation. This study highlights that morphological descriptions alongside molecular characterisation remain crucial if we are to gain an understanding of the true diversity and host specificity of protozoan parasites in Australia and elsewhere.