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Aim: Macroecological analyses provide valuable insights into factors that influence how parasites are distributed across space and among hosts. Amid large uncertainties that arise when generalizing from local and regional findings, hierarchical approaches applied to global datasets are required to determine whether drivers of parasite infection patterns vary across scales. We assessed global patterns of haemosporidian infections across a broad diversity of avian host clades and zoogeographical realms to depict hotspots of prevalence and to identify possible underlying drivers. Location: Global. Time period: 1994–2019. Major taxa studied: Avian haemosporidian parasites (genera Plasmodium, Haemoproteus, Leucocytozoon and Parahaemoproteus). Methods: We amalgamated infection data from 53,669 individual birds representing 2,445 species world‐wide. Spatio‐phylogenetic hierarchical Bayesian models were built to disentangle potential landscape, climatic and biotic drivers of infection probability while accounting for spatial context and avian host phylogenetic relationships. Results: Idiosyncratic responses of the three most common haemosporidian genera to climate, habitat, host relatedness and host ecological traits indicated marked variation in host infection rates from local to global scales. Notably, host ecological drivers, such as migration distance for Plasmodium and Parahaemoproteus, exhibited predominantly varying or even opposite effects on infection rates across regions, whereas climatic effects on infection rates were more consistent across realms. Moreover, infections in some low‐prevalence realms were disproportionately concentrated in a few local hotspots, suggesting that regional‐scale variation in habitat and microclimate might influence transmission, in addition to global drivers. Main conclusions: Our hierarchical global analysis supports regional‐scale findings showing the synergistic effects of landscape, climate and host ecological traits on parasite transmission for a cosmopolitan and diverse group of avian parasites. Our results underscore the need to account for such interactions, in addition to possible variation in drivers across regions, to produce the robust inference required to predict changes in infection risk under future scenarios. [ABSTRACT FROM AUTHOR]

Metatranscriptomics is a powerful method for studying the composition and function of complex microbial communities. The application of metatranscriptomics to multispecies parasite infections is of particular interest, as research on parasite evolution and diversification has been hampered by technical challenges to genome‐scale DNA sequencing. In particular, blood parasites of vertebrates are abundant and diverse although they often occur at low infection intensities and exist as multispecies infections, rendering the isolation of genomic sequence data challenging. Here, we use birds and their diverse haemosporidian parasites to illustrate the potential for metatranscriptome sequencing to generate large quantities of genome‐wide sequence data from multiple blood parasite species simultaneously. We used RNA‐sequencing of 24 blood samples from songbirds in North America to show that metatranscriptomes can yield large proportions of haemosporidian protein‐coding gene repertoires even when infections are of low intensity (<0.1% red blood cells infected) and consist of multiple parasite taxa. By bioinformatically separating host and parasite transcripts and assigning them to the haemosporidian genus of origin, we found that transcriptomes detected ~23% more total parasite infections across all samples than were identified using microscopy and DNA barcoding. For single‐species infections, we obtained data for >1,300 loci from samples with as low as 0.03% parasitaemia, with the number of loci increasing with infection intensity. In total, we provide data for 1,502 single‐copy orthologous loci from a phylogenetically diverse set of 33 haemosporidian mitochondrial lineages. The metatranscriptomic approach described here has the potential to accelerate ecological and evolutionary research on haemosporidians and other diverse parasites. See also the perspective by Loren Cassin‐Sackett [ABSTRACT FROM AUTHOR]

Co‐infections with multiple parasite taxa are ubiquitous in nature and have the potential to impact the co‐evolutionary dynamics between host and parasite, though patterns of phylogenetic community structure of co‐infecting parasites and the processes that generate these patterns have rarely been studied across diverse host–parasite communities.Here, we tested for the roles of host and parasite evolutionary history as well as environmental variables as drivers of phylogenetic community structure among co‐infecting haemosporidian (malaria) parasites and their avian hosts in the North American boreal forest, a region characterized by an extraordinarily high blood parasite co‐infection rate.We used multiple methods to identify non‐random patterns of co‐infection among parasite species and determined whether these patterns were influenced more by co‐evolutionary host associations or environmental variables. We used model‐based approaches to test whether parasites that occurred together in a single host individual exhibited phylogenetic clustering or overdispersion. Lastly, we tested whether the observed phylogenetic community structure could be explained by parasites having convergently evolved similar patterns of host associations.We found that haemosporidian parasite co‐infections occurred at a high frequency in the boreal forest system and that parasite taxa co‐occurred in significantly non‐random patterns within host individuals and among host species. Parasite taxa that occurred in co‐infections tended to be phylogenetically overdispersed. We show that this pattern of phylogenetic overdispersion can be attributed largely to the effect of evolutionarily labile, convergent host associations that have resulted in the pool of parasites that have the potential to infect a given host consisting nearly exclusively of distantly related lineages.Our findings illustrate that environmental filtering of convergent traits can produce phylogenetically overdispersed communities, even at the level of co‐infecting parasites within an individual host organism. Broadly, this analysis illustrates how co‐evolutionary history can have a strong influence on the modern phylogenetic community assembly of diverse host–symbiont communities. [ABSTRACT FROM AUTHOR]

Variation in susceptibility is ubiquitous in multi‐host, multi‐parasite assemblages, and can have profound implications for ecology and evolution in these systems. The extent to which susceptibility to parasites is phylogenetically conserved among hosts can be revealed by analysing diverse regional communities. We screened for haemosporidian parasites in 3983 birds representing 40 families and 523 species, spanning ~ 4500 m elevation in the tropical Andes. To quantify the influence of host phylogeny on infection status, we applied Bayesian phylogenetic multilevel models that included a suite of environmental, spatial, temporal, life history and ecological predictors. We found evidence of deeply conserved susceptibility across the avian tree; host phylogeny explained substantial variation in infection status, and results were robust to phylogenetic uncertainty. Our study suggests that susceptibility is governed, in part, by conserved, latent aspects of anti‐parasite defence. This demonstrates the importance of deep phylogeny for understanding present‐day ecological interactions. [ABSTRACT FROM AUTHOR]

Abstract: Most tropical bird species have narrow elevational ranges, likely reflecting climatic specialization. This is consistent with Janzen's Rule, the tendency for mountain passes to be effectively “higher” in the tropics. Hence, those few tropical species that occur across broad elevational gradients (elevational generalists) represent a contradiction to Janzen's Rule. Here, we aim to address the following questions. Are elevational generalists being sundered by diversifying selection along the gradient? Does elevational movement cause these species to resist diversification or specialization? Have they recently expanded, suggesting that elevational generalism is short‐lived in geological time? To answer these questions, we tested for differentiation, movement and expansion in four elevational generalist songbird species on the Andean west slope. We used morphology and mtDNA to test for genetic differentiation between high‐ and low‐elevation populations. To test for elevational movements, we measured hydrogen isotope (δ2H) values of metabolically inert feathers and metabolically active liver. Morphology differed for House Wren (Troglodytes aedon) and Hooded Siskin (Spinus magellanicus), but not for Cinereous Conebill (Conirostrum cinereum) and Rufous‐collared Sparrow (Zonotrichia capensis) respectively. mtDNA was structured by elevation only in Z. capensis. δ2H data indicated elevational movements by two tree‐ and shrub‐foraging species with moderate‐to‐high vagility (C. cinereum and S. magellanicus), and sedentary behaviour by two terrestrial‐foraging species with low‐to‐moderate vagility (T. aedon and Z. capensis). In S. magellanicus, elevational movements and lack of mtDNA structure contrast with striking morphological divergence, suggesting strong diversifying selection on body proportions across the c. 50 km gradient. All species except C. cinereum exhibited mtDNA haplotype variation consistent with recent population expansion across the elevational gradient, potentially concurrent with Holocene anthropogenic habitat conversion for agriculture. In different ways, each species defies the tendency for tropical birds to have long‐term stable distributions and sedentary habits. We conclude that tropical elevational generalism is rare due to evolutionary instability. [ABSTRACT FROM AUTHOR]

Recent research has revealed well over 1000 mtDNA lineages of avian haemosporidian parasites, but the extent to which this diversity is caused by host - parasite coevolutionary history or environmental heterogeneity is unclear. We surveyed haemosporidian and host mtDNA in a geographically structured, ecological generalist species, the house wren Troglodytes aedon, across the complex landscape of the Peruvian Andes. We detected deep genetic structure within the house wren across its range, represented by seven clades that were between 3.4 - 5.7% divergent. From muscle and liver tissue of 140 sampled house wrens we found 23 divergent evolutionary lineages of haemosporidian mtDNA, of which ten were novel and apparently specific to the house wren based on searches of haemosporidian databases. Combined and genus-specific haemosporidian abundance diff ered significantly across environments and elevation, with Leucocytozoon parasites strongly associated with montane habitats. We observed spatial stratification of haemosporidians along the west slope of the Andes where fi ve lineages were restricted to non-overlapping elevational bands. Individual haemosporidian lineages varied widely with respect to host specificity, prevalence, and geographic distribution, with the most host-generalist lineages also being the most prevalent and widely distributed. Despite the deep divergences within the house wren, we found no evidence for host-specific co-diversification with haemosporidians. Instead, host-specific haemosporidian lineages in the genus Haemoproteus were polyphyletic with respect to the New World parasite fauna and appeared to have diversified by periodic host-switches involving distantly related avian species within the same region. Th ese host-specific lineages appeared to have diversified contemporaneously with Andean house wrens. Taken together, these fi ndings suggest a model of diff use co-diversification in which host and parasite clades have diversified over the same time period and in the same geographic area, but with parasites having limited or ephemeral host specificity. [ABSTRACT FROM AUTHOR]