Host phylogeny matters: Examining sources of variation in infection risk by blood parasites across a tropical montane bird community in India

Digenea community structure of the Salema, Sarpa salpa (Linnaeus, 1758) (Teleostei, Sparidae), from the Central coast of Algeria

The main goal of the current work was to describe and analyse the Digenean community structure in Sarpa salpa. A total of 114 specimens of S. salpa were collected from the Central Coast of Algeria at six localities. The fish were immediately transported to the laboratory to be examined for digeneans. From 107 of the 114 S. salpa examined, a total of 8,722 specimens of seven species belonging to three families were recovered. Among them, Robphildollfusium fractum and Mesometra orbicularis were the most prevalent and abundant species. Moreover, Lepocreadium album was found for the first time in S. salpa from the coast of Algeria, and Centroderma spinosissima and Wardula capitellata represent new parasites to the Algerian digenean fauna that infect teleost fish. The component community of these Digeneans is characterised by R. fractum as its dominant species representing 62% of the total number of collected Digeneans, as well by a Shannon diversity index (H') and Dominance Simpson index (D) of 1.03 and 2.23, respectively. According to Spearman's correlation test, Mesometra brachycoelia and W. capitellata were negatively correlated to the host biological factors. On the other hand, R. fractum showed a positive correlation between its mean abundance and the total length of the fish. With these findings, we provided the component structure of the Digenean fauna of S. salpa and highlighted their diversity, contributing to the biodiversity of the parasitic Platyhelminthes in Algeria.

Avian haemosporidians of breeding birds in the Davis Mountains sky-islands of west Texas, USA

Avian haemosporidians are protozoan parasites transmitted by insect vectors that infect birds worldwide, negatively impacting avian fitness and survival. However, the majority of haemosporidian diversity remains undescribed. Quantifying this diversity is critical to determining parasite–host relationships and host-switching potentials of parasite lineages as climate change induces both host and vector range shifts. In this study, we conducted a community survey of avian haemosporidians found in breeding birds on the Davis Mountains sky islands in west Texas, USA. We determined parasite abundance and host associations and compared our results to data from nearby regions. A total of 265 birds were screened and infections were detected in 108 birds (40.8%). Most positive infections were identified as Haemoproteus (36.2%), followed by Plasmodium (6.8%) and Leucocytozoon (0.8%). A total of 71 haemosporidian lineages were detected of which 39 were previously undescribed. We found that regional similarity influenced shared lineages, as a higher number of lineages were shared with avian communities in the sky islands of New Mexico compared to south Texas, the Texas Gulf Coast and central Mexico. We found that migratory status of avian host did not influence parasite prevalence, but that host phylogeny is likely an important driver.

Host phylogeny shapes viral transmission networks in an island ecosystem

Virus transmission between host species underpins disease emergence. Both host phylogenetic relatedness and aspects of their ecology, such as species interactions and predator-prey relationships, may govern rates and patterns of cross-species virus transmission and hence zoonotic risk. To address the impact of host phylogeny and ecology on virus diversity and evolution, we characterized the virome structure of a relatively isolated island ecological community in Fiordland, New Zealand, that are linked through a food web. We show that phylogenetic barriers that inhibited cross-species virus transmission occurred at the level of host phyla (between the Chordata, Arthropoda and Streptophyta) as well as at lower taxonomic levels. By contrast, host ecology, manifest as predator-prey interactions and diet, had a smaller influence on virome composition, especially at higher taxonomic levels. The virus-host community comprised a 'small world' network, in which hosts with a high diversity of viruses were more likely to acquire new viruses, and generalist viruses that infect multiple hosts were more likely to infect additional species compared to host specialist viruses. Such a highly connected ecological community increases the likelihood of cross-species virus transmission, particularly among closely related species, and suggests that host generalist viruses present the greatest risk of disease emergence.

Human disturbance increases coronavirus prevalence in bats

Human land modification is a known driver of animal-to-human transmission of infectious agents (zoonotic spillover). Infection prevalence in the reservoir is a key predictor of spillover, but landscape-level associations between the intensity of land modification and infection rates in wildlife remain largely untested. Bat-borne coronaviruses have caused three major disease outbreaks in humans: severe acute respiratory syndrome (SARS), Middle East respiratory syndrome, and coronavirus disease 2019 (COVID-19). We statistically link high-resolution land modification data with bat coronavirus surveillance records and show that coronavirus prevalence significantly increases with the intensity of human impact across all climates and levels of background biodiversity. The most significant contributors to the overall human impact are agriculture, deforestation, and mining. Regions of high predicted bat coronavirus prevalence coincide with global disease hotspots, suggesting that infection prevalence in wildlife may be an important factor underlying links between human land modification and zoonotic disease emergence.

Haemosporidian parasites and incubation period influence plumage coloration in tanagers (Passeriformes: Thraupidae)

Birds are highly visually oriented and use plumage coloration as an important signalling trait in social communication. Hence, males and females may have different patterns of plumage coloration, a phenomenon known as sexual dichromatism. Because males tend to have more complex plumages, sexual dichromatism is usually attributed to female choice. However, plumage coloration is partly condition-dependent; therefore, other selective pressures affecting individuals' success may also drive the evolution of this trait. Here, we used tanagers as model organisms to study the relationships between dichromatism and plumage coloration complexity in tanagers with parasitism by haemosporidians, investment in reproduction and life-history traits. We screened blood samples from 2849 individual birds belonging to 52 tanager species to detect haemosporidian parasites. We used publicly available data for plumage coloration, bird phylogeny and life-history traits to run phylogenetic generalized least-square models of plumage dichromatism and complexity in male and female tanagers. We found that plumage dichromatism was more pronounced in bird species with a higher prevalence of haemosporidian parasites. Lastly, high plumage coloration complexity in female tanagers was associated with a longer incubation period. Our results indicate an association between haemosporidian parasites and plumage coloration suggesting that parasites impact mechanisms of sexual selection, increasing differences between the sexes, and social (non-sexual) selection, driving females to develop more complex coloration.

Host phylogeny and ecology, but not host physiology, are the main drivers of (dis)similarity between the host spectra of fleas: application of a novel ordination approach to regional assemblages from four continents

We investigated the patterns of phylogenetic and functional (dis)similarity in the species composition of host spectra between co-habitating generalist flea species in regional assemblages from four continents (Europe, Asia, North America and Africa) using a recently developed ordination approach (Double Similarity Principal Component Analysis). From the functional perspective, we considered physiological [body mass and basal metabolic rate (BMR)] and ecological (shelter depth and complexity) host traits. We asked (a) whether host phylogeny, physiology or ecology is the main driver of (dis)similarities between flea host spectra and (b) whether the patterns of phylogenetic and functional (dis)similarity in host spectra vary between flea assemblages from different continents. Phylogenetic similarity between the host spectra was highest in Africa, lowest in North America and moderate in Europe and Asia. In each assemblage, phylogenetic clusters of hosts dominating in the host spectra could be distinguished. The functional similarity between the host spectra of co-occurring fleas was low for shelter structure in all assemblages and much higher for body mass and BMR in three of the four assemblages (except North America). We conclude that host phylogeny and shelter structure are the main drivers of (dis)similarity between the host spectra of co-habitating fleas. However, the effects of these factors on the patterns of (dis)similarity varied across continents.

Impacts of selective logging on haemosporidian infection and physiological correlates in tropical birds

Tropical forest degradation affects host-parasite interactions, determining the probability of animals acquiring an infection. The activation of an immune response to fight off infections requires energy and other resources such as antioxidants which may be redirected from growth and reproduction. A key question is how selective logging-the most common form of tropical forest degradation-impacts the prevalence of avian haemosporidian infection and its correlated physiological responses (nutritional and oxidative status markers). We investigated the prevalence of Plasmodium, Haemoproteus, and Leucocytozoon parasites in 14 understorey bird species in lowland, logged and unlogged, old-growth forests of Borneo. Prevalences of infections were similar between selectively logged and unlogged forests. To explore nutritional and oxidative status effects of haemosporidian infections, we examined associations between infections and plasma proteins, plasma triglycerides, and multiple blood-based markers of oxidative status, testing for an impact of selective logging on those markers. Birds infected with Plasmodium showed higher levels of plasma proteins and non-enzymatic antioxidant capacity, and lower levels of plasma triglycerides and glutathione, compared with haemosporidian-free individuals. Conversely, birds infected with Haemoproteus showed no changes in nutritional or physiological markers compared with uninfected individuals. These results indicate higher metabolic and physiological costs of controlling Plasmodium infection, compared with Haemoproteus, possibly due to higher pathogenicity of Plasmodium. Selectively logged forests had no effect on the responses of birds to infection, suggesting that the environmental conditions of degraded forests do not appear to induce any appreciable physiological demands in parasitised birds.

Anthropogenic disturbance favours generalist over specialist parasites in bird communities: Implications for risk of disease emergence

Niche theory predicts specialists which will be more sensitive to environmental perturbation compared to generalists, a hypothesis receiving broad support in free-living species. Based on their niche breadth, parasites can also be classified as specialists and generalists, with specialists infecting only a few and generalists a diverse array of host species. Here, using avian haemosporidian parasites infecting wild bird populations inhabiting the Western Ghats, India as a model system, we elucidate how climate, habitat and human disturbance affects parasite prevalence both directly and indirectly via their effects on host diversity. Our data demonstrate that anthropogenic disturbance acts to reduce the prevalence of specialist parasite lineages, while increasing that of generalist lineages. Thus, as in free-living species, disturbance favours parasite communities dominated by generalist versus specialist species. Because generalist parasites are more likely to cause emerging infectious diseases, such biotic homogenisation of parasite communities could increase disease emergence risk in the Anthropocene.

Specialist versus generalist parasites: the interactions between host diversity, environment and geographic barriers in avian malaria

The specialist versus generalist strategies of hemoparasites in relation to their avian host, as well as environmental factors, can influence their prevalence, diversity and distribution. In this paper we investigated the influence of avian host species, as well as the environmental and geographical factors, on the strategies of Haemoproteus and Plasmodium hemoparasites. We determined prevalence and diversity by targeting their cytochrome b (Cytb) in a total of 2,590 passerine samples from 138 localities of Central and South America, and analysed biogeographic patterns and host-parasite relationships. We found a total prevalence of 23.2%. Haemoproteus presented a higher prevalence (15.3%) than Plasmodium (4.3%), as well as a higher diversity and host specificity. We determined that Plasmodium and Haemoproteus prevalences correlated positively with host diversity (Shannon index) and were significantly influenced by bird diversity, demonstrating a possible "amplification effect". We found an effect of locality and the avian family for prevalences of Haemoproteus and Plasmodium. These results suggest that Haemoproteus is more specialist than Plasmodium and could be mostly influenced by its avian host and the Andes Mountains.

Characterization of the Plasmodium and Haemoproteus parasite community in temperate-tropical birds during spring migration

Animal movements, especially avian migration, can be a mechanism for the large-scale dispersal and geographic range expansion of parasites. The host-parasite relationships among birds during migration have yet to be fully explored. We characterized the haemosporidian parasite lineages in passerines during spring migration on the Texas coast of the Gulf of Mexico, and identified associations among wintering origin (US, Central America, South America) and foraging height (canopy, understory, ground) and infection status. We examined 743 samples representing 52 species of 10 families over six years, 2014-2019. We used PCR and DNA sequencing of the haemosporidian cytB gene from avian blood samples to determine infection status with the genera Plasmodium and Haemoproteus and characterize the lineages of blood parasites. We found an overall haemosporidian infection prevalence of 48.4% among neotropical migrant and Texas wintering birds. Among families, Icterids had the highest prevalence (75%, 24 individuals, 4 species sampled) whereas Parulids had the lowest prevalence (38.4%, 177 individuals, 18 species sampled). Among infected birds, Plasmodium spp. infections were more common than Haemoproteus spp. infections in species that winter in Central America compared to those that winter in the US or South America. Similarly, among infected birds, Plasmodium spp. infections were more common than Haemoproteus spp. infections in species that forage on the ground or in the understory compared to those that forage in the canopy. Infected birds harbored 65 different haemosporidian lineages (71% Plasmodium; 29% Haemoproteus) of which 17 lineages have never previously been reported and six lineages were documented for the first time in North America, having been previously detected only in Central or South America. These data are consistent with the premise that intercontinental parasite dispersal may be facilitated by passerine birds. Future studies focused on surveillance, the probability of establishment of parasite lineages, and the use of individual bird tracking methods to understand infection dispersion over time will allow a more comprehensive understanding of changing avian host-haemosporidian relationships.