Prevalence of blood parasites in European passeriform birds

Repeatability of feather mite prevalence and intensity in passerine birds

Understanding why host species differ so much in symbiont loads and how this depends on ecological host and symbiont traits is a major issue in the ecology of symbiosis. A first step in this inquiry is to know whether observed differences among host species are species-specific traits or more related with host-symbiont environmental conditions. Here we analysed the repeatability (R) of the intensity and the prevalence of feather mites to partition within- and among-host species variance components. We compiled the largest dataset so far available: 119 Paleartic passerine bird species, 75,944 individual birds, ca. 1.8 million mites, seven countries, 23 study years. Several analyses and approaches were made to estimate R and adjusted repeatability (R(adj)) after controlling for potential confounding factors (breeding period, weather, habitat, spatial autocorrelation and researcher identity). The prevalence of feather mites was moderately repeatable (R = 0.26-0.53; R(adj) = 0.32-0.57); smaller values were found for intensity (R = 0.19-0.30; R(adj )= 0.18-0.30). These moderate repeatabilities show that prevalence and intensity of feather mites differ among species, but also that the high variation within species leads to considerable overlap among bird species. Differences in the prevalence and intensity of feather mites within bird species were small among habitats, suggesting that local factors are playing a secondary role. However, effects of local climatic conditions were partially observed for intensity.

Mixed species flock, nest height, and elevation partially explain avian haemoparasite prevalence in Colombia

The high avian biodiversity present in the Neotropical region offers a great opportunity to explore the ecology of host-parasite relationships. We present a survey of avian haemoparasites in a megadiverse country and explore how parasite prevalences are related to physical and ecological host characteristics. Using light microscopy, we documented the presence of haemoparasites in over 2000 individuals belonging to 246 species of wild birds, from nine localities and several ecosystems of Colombia. We analysed the prevalence of six avian haemoparasite taxa in relation to elevation and the following host traits: nest height, nest type, foraging strata, primary diet, sociality, migratory behaviour, and participation in mixed species flocks. Our analyses indicate significant associations between both mixed species flocks and nest height and Haemoproteus and Leucocytozoon prevalence. The prevalence of Leucocytozoon increased with elevation, whereas the prevalence of Trypanosoma and microfilariae decreased. Plasmodium and Haemoproteus prevalence did not vary significantly with elevation; in fact, both parasites were found up to 3300m above sea level. The distribution of parasite prevalence across the phylogeny of bird species included in this study showed little host phylogenetic signal indicating that infection rates in this system are evolutionarily labile. Vector distribution as well as the biology of transmission and the maintenance of populations of avian haemoparasites deserve more detailed study in this system.

Avian malaria in New Zealand

Avian malaria parasites of the genus Plasmodium have the ability to cause morbidity and mortality in naïve hosts, and their impact on the native biodiversity is potentially serious. Over the last decade, avian malaria has aroused increasing interest as an emerging disease in New Zealand with some endemic avian species, such as the endangered mohua (Mohua ochrocephala), thought to be particularly susceptible. To date, avian malaria parasites have been found in 35 different bird species in New Zealand and have been diagnosed as causing death in threatened species such as dotterel (Charadrius obscurus), South Island saddleback (Philesturnus carunculatus carunculatus), mohua, hihi (Notiomystis cincta) and two species of kiwi (Apteryx spp.). Introduced blackbirds (Turdus merula) have been found to be carriers of at least three strains of Plasmodium spp. and because they are very commonly infected, they are likely sources of infection for many of New Zealand's endemic birds. The spread and abundance of introduced and endemic mosquitoes as the result of climate change is also likely to be an important factor in the high prevalence of infection in some regions and at certain times of the year. Although still limited, there is a growing understanding of the ecology and epidemiology of Plasmodium spp. in New Zealand. Molecular biology has played an important part in this process and has markedly improved our understanding of the taxonomy of the genus Plasmodium. This review presents our current state of knowledge, discusses the possible infection and disease outcomes, the implications for host behaviour and reproduction, methods of diagnosis of infection, and the possible vectors for transmission of the disease in New Zealand.

Spatial, temporal, molecular, and intraspecific differences of haemoparasite infection and relevant selected physiological parameters of wild birds in Georgia, USA

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Variable prevalences of different haemoparasite species noted among passerine hosts.

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Different foraging guilds associated with different haemoparasite infections.

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Prevalence of Haemoproteus, Plasmodium, and Trypanosoma higher in breeding season.

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PCV differences noted between bird species but no effect of haemoparasites on PCV or polychromasia.

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Novel haplotypes detected and new geographic and host associations noted for seven haplotypes.

The prevalence of five avian haemoparasite groups was examined for effects on health and associations with extrinsic factors. Overall, 786 samples were examined from six sites in two Georgia (USA) watersheds, during breeding and non-breeding periods in 2010 and 2011. Among the four most commonly infected species, Haemoproteus prevalence was significantly higher in Northern Cardinals (Cardinalis cardinalis) compared to Indigo Buntings (Passerina cyanea) and Tufted Titmice (Baeolophus bicolor) while prevalence in White-throated Sparrows (Zonotrichia albicollis) was significantly higher than in Indigo Buntings. Higher prevalence of Plasmodium was noted in Tufted Titmice and Northern Cardinals. While Leucocytozoon prevalence was highest in White-throated Sparrows, Trypanosoma prevalence was highest in Tufted Titmice. Interesting differences in infection probabilities were noted between foraging guilds with Haemoproteus associated with low-middle level strata and birds in the middle-upper strata were more likely to be infected with Plasmodium and Trypanosoma. In contrast, ground-foraging birds were more likely to be infected with Leucocytozoon. Breeding season was correlated with higher polychromasia counts and higher prevalence of Haemoproteus, Plasmodium and Trypanosoma. In addition, prevalence of infection with certain haemoparasite genera and packed cell volume (PCV) were different among host species. Body mass index was inversely correlated with prevalence of microfilaria infection but positively related to Haemoproteus infection. However, we found no relationship between PCV or polychromasia levels with haemoparasite infection. Molecular characterization of 61 samples revealed 19 unique Haemoproteus (n = 7) and Plasmodium (n = 12) haplotypes with numerous new host records. No differences were noted in haplotype diversity among birds with different migratory behaviors or foraging heights, thus additional studies are needed that incorporate molecular analysis, host biology, and vector biology into comprehensive models on parasite ecology. Detailed morphological examination of these parasites is also necessary to determine if closely related haplotypes represent single species or morphologically distinct, but closely related, haplotypes.

Altitudinal variation in haemosporidian parasite distribution in great tit populations

BACKGROUND

One 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.

METHODS

In 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.

RESULTS

High 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.

CONCLUSIONS

Avian 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.

Avian haemosporidian persistence and co-infection in great tits at the individual level

Background

Many studies have tracked the distribution and persistence of avian haemosporidian communities across space and time at the population level, but few studies have investigated these aspects of infection at the individual level over time. Important aspects of parasite infection at the individual level can be missed if only trends at the population level are studied. This study aimed to determine how persistent Haemosporida are in great tit individuals recaptured over several years, whether parasitaemia differed by parasite lineage (mitochondrial cytochrome b haplotype) and how co-infection (i.e. concurrent infection with multiple genera of parasites) affects parasitaemia and body mass.

Methods

Parasite prevalence was determined by polymerase chain reaction (PCR), quantitative PCR were used to assess parasitaemia and sequencing was employed to determine the identity of the lineages using the MalAvi database.

Results

Haemosporidian prevalence was high over sampled years with 98% of 55 recaptured individuals showing infection in at least one year of capture. Eighty-two percent of all positive individuals suffered co-infection, with an overall haemosporidian lineage diversity of seventeen. Plasmodium and Haemoproteus parasites were found to be highly persistent, with lineages from these genera consistently found in individuals across years and with no differences in individual parasitaemia being recorded at subsequent captures. Conversely, Leucocytozoon parasites showed higher turnover with regard to lineage changes or transitions in infection status (infected vs non-infected) across years. Parasitaemia was found to be lineage specific and there was no relationship between Plasmodium parasitaemia or host body condition and the presence of Leucocytozoon parasites.

Conclusions

The findings of this study suggest that different genera of haemosporidian parasites interact differently with their host and other co-infecting parasites, influencing parasite persistence most likely through inter-parasite competition or host-parasite immune interactions. Even-though co-infections do not seem to result in increased virulence (higher parasitaemia or poorer host body condition), further investigation into infection potential of these parasites, both individually and as co-infections, is necessary.

Immune investment is explained by sexual selection and pace-of-life, but not longevity in parrots (Psittaciformes)

Investment in current reproduction should come at the expense of traits promoting future reproduction, such as immunity and longevity. To date, comparative studies of pace-of-life traits have provided some support for this, with slower paced species having greater immune function. Another means of investment in current reproduction is through secondary sexual characters (SSC). Investment in SSC's is considered costly, both in terms of immunity and longevity, with greater costs being borne by species with more elaborate traits. Yet within species, females prefer more ornate males and those males are typically immunologically superior. Because of this, predictions about the relationship between immunity and SSC's across species are not clear. If traits are costly, brighter species should have reduced immune function, but the opposite is true if SSC's arise from selection for more immunocompetent individuals. My approach was to investigate immune investment in relation to SSC's, pace-of-life and longevity while considering potentially confounding ecological factors. To do so I assessed leukocyte counts from in a novel group, the Psittaciformes. Investment in SSC's best explained investment in immunity: species with brighter plumage had higher leukocyte counts and those with a greater degree of sexual dichromatism had fewer. Ecological variables and pace-of-life models tended to be poor predictors of immune investment. However, shorter incubation periods were associated with lower leukocyte counts supporting the notion that species with a fast pace-of-life invest less in immunity. These results suggest that investment in reproduction in terms of fast pace-of-life and sexual dichromatism results in reduced immunity; however, investment in plumage colour per se does not impose a cost on immunity across species.

Structure and organization of an avian haemosporidian assemblage in a Neotropical savanna in Brazil

Studies on avian haemosporidia are on the rise, but we still lack a basic understanding of how ecological and evolutionary factors mold the distributions of haemosporidia among species in the same bird community. We studied the structure and organization of a local avian haemosporidian assemblage (genera Plasmodium and Haemoproteus) in the Cerrado biome of Central Brazil for 5 years. We obtained 790 blood samples from 54 bird species of which 166 (21%) were infected with haemosporidians based on molecular diagnostics. Partial sequences of the parasite cytochrome b gene revealed 18 differentiated avian haemosporidian lineages. We also analysed the relationship of life-history traits (i.e., nesting height, migration status, nest type, sociality, body mass, and embryo development period) of the 14 most abundant bird species with the prevalence of avian haemosporidia. It was found that host species that bred socially presented a higher prevalence of Haemoproteus (Parahaemoproteus) than bird species that bred in pairs. Thus, aspects of host behaviour could be responsible for differential exposure to vectors. The assemblage of avian haemosporidia studied here also confirms a pattern that is emerging in recent studies using molecular markers to identify avian haemosporidians, namely that many lineages are host generalists.

Prevalence of Hemoproteus iwa in Galapagos great frigatebirds (Fregata minor) and their obligate fly ectoparasite (Olfersia spinifera)

The prevalence of hemosporidian parasites varies among different host species, geographic locations, habitats, and host life histories, and yet we do not have a firm understanding of the ultimate causes of the variation. Seabirds are not typically found infected with hemosporidian parasites; however, frigatebird species have been repeatedly documented with Hemoproteus spp. infections. Hemoproteus iwa in Galapagos great frigatebirds (Fregata minor) is vectored by a hippoboscid fly, Olfersia spinifera , an obligate ectoparasite of the bird host. Five populations of Galapagos great frigatebirds, and flies collected from the birds, were sampled and tested for H. iwa . Prevalence did not differ across 4 yr or between 5 islands, but males were found to have a significantly higher prevalence of infection than did females. Additionally, juveniles were more likely to be infected than were adults and chicks. Because the invertebrate vector is an obligate parasite, we were able to estimate prevalence in the vector as well as in the particular host upon which it fed, a task that is impossible, or nearly impossible, in hemosporidian parasites vectored by midges or mosquitoes. We tested the correlation between the infection status of the bird host and the infection status of the fly collected from the bird. More often than not the 2 were correlated, but some mismatches were found. Using the occurrence of infected flies on uninfected birds (12/99) as a proxy for transmission potential, we can estimate the transmission rate to be between 5 and 20% (95% confidence intervals) among individual vertebrate hosts.

Naturalists, natural history, and the nature of biological diversity

Abstract In this essay, I argue that natural history--observing the natural world and deciphering its patterns--is as essential today as it was during Darwin's lifetime to the continuing development of ecology and evolutionary biology. This tradition, which I illustrate through the example of E. O. Wilson's discovery of the taxon cycle 50 years ago, is still very much alive, but there is a growing tendency for observation to serve theory rather provide new insight or to test the predictions of theory. This tendency manifests itself in the failure of ideas about the diversity, distribution, and abundance of species to be informed by patterns in nature that are readily apparent. On the one hand, supporters of neutral theory have sidestepped the unrealistically slow dynamics of random processes in large metacommunities, and they have failed to note global correlations in species numbers and population sizes within taxa. On the other hand, proponents of niche theory have disregarded the implications of variation in distribution and abundance among close relatives, which implies population regulation largely by species-specific agents, such as pathogens. Nor has community niche theory addressed the independence of distribution and abundance with respect to number of close relatives (and presumed competitors). The diversity, abundances, and distributions of species represent the unfolding of many processes over a historically and geographically contingent landscape, for which experimental methods of scientific inquiry are poorly suited. To interpret patterns of diversity, we must continue to depend on inductive reasoning inspired by the data of natural history.

Blood parasites, body condition, and wing length in two subspecies of yellow wagtail (Motacilla flava) during migration

Blood parasites of migrating yellow wagtails of two subspecies--Motacilla flava feldegg and Motacilla flava flava-were studied on a sample of 473 birds caught in spring and autumn periods in Bulgaria. We controlled eight "migration waves" (flocks captured in different evenings) of yellow wagtails for four parameters--average body mass, average fat level, average wing length, and average prevalence of different hematozoan species. Gametocytes or meronts of a total of six species of hematozoa belonging to three genera were identified-Haemoproteus motacillae, Haemoproteus anthi, Plasmodium relictum, Plasmodium subpraecox, Plasmodium cathemerium, and Tryponosoma avium. Mixed infections were detected in 31 cases, of which 14 were of H. anthi/H. motacillae type. Parasite species composition was similar in the two studied subspecies of M. flava. We did not find any significant differences in the overall infection prevalence or number of infecting parasites between M. f. flava and M. f. feldegg. Parasite prevalence and the number of co-infecting parasites in spring were much higher than in fall. Season had a strong influence on the prevalence of H. anthi and H. motacillae, and for both, there was a marginally significant interaction between subspecies and season, but not a season-independent influence of subspecies. Males of M. f. feldegg had a significantly higher overall blood parasite prevalence and prevalence of H. anthi than females. Sex-related differences in the prevalence of other parasites were not significant. Migration waves of yellow wagtails differed in overall infection status and in H. motacillae prevalence, but not for H. anthi prevalence. We also found significant differences in fat score, weight, and wing length between the studied migration waves of the yellow wagtails. Fat scores of birds infected with different hematozoa were lower compared with those of the non-infected birds. This only marginally was true for body weight and was not the case for wing length. Overall, infected birds were in worse condition (estimated as the residual weight after regression with wing length) compared with the non-infected birds, but after controlling for seasonal effects, the differences in condition appeared to be due to migration season and did not significantly differ between infected and non-infected birds caught in the same season.

Low prevalence of Haemoproteus infections in Chiffchaffs

Parasite prevalence is an important variable in many evolutionary and ecological studies. In birds, haemosporidian blood parasites have been in focus of many comparative analyses. Because low prevalence is difficult to estimate precisely and that studies finding low prevalence are more likely to remain unpublished, our knowledge of parasite prevalence is biased towards highly infected taxa. Species with naturally low levels of infection are nonetheless interesting as they may provide models for studying the evolution of pathogen resistance. In the present study we show that the prevalence of Haemoproteus parasites is markedly lower in several taxa within the widely distributed chiffchaff species-complex compared to other species within the genus Phylloscopus. Since chiffchaffs, P. collybita, commonly coexists in the same habitat as congeners frequently infected with Haemoproteus parasites, immediate ecological variables like abundance of vectors can hardly explain this difference. Some of the parasites infecting coexisting congeners are broad host generalists leaving it enigmatic why chiffchaffs are almost free of Haemoproteus infections. We propose that detailed infection experiments are needed to illuminate whether chiffchaffs possess a genetic immunity against Haemoproteus parasites or if other more subtle ecological processes, like anti-vector behaviour, play a role in its generally low level of infestation.

Prevalence of blood parasites in seabirds - a review

INTRODUCTION

While blood parasites are common in many birds in the wild, some groups seem to be much less affected. Seabirds, in particular, have often been reported free from blood parasites, even in the presence of potential vectors.

RESULTS

From a literature review of hemosporidian prevalence in seabirds, we collated a dataset of 60 species, in which at least 15 individuals had been examined. These data were included in phylogenetically controlled statistical analyses of hemosporidian prevalence in relation to ecological and life-history parameters. Haemoproteus parasites were common in frigatebirds and gulls, while Hepatozoon occurred in albatrosses and storm petrels, and Plasmodium mainly in penguins. The prevalence of Haemoproteus showed a geographical signal, being lower in species with distribution towards polar environments. Interspecific differences in Plasmodium prevalence were explained by variables that relate to the exposure to parasites, suggesting that prevalence is higher in burrow nesters with long fledgling periods. Measures of Plasmodium, but not Haemoproteus prevalences were influenced by the method, with PCR-based data resulting in higher prevalence estimates.

CONCLUSIONS

Our analyses suggest that, as in other avian taxa, phylogenetic, ecological and life-history parameters determine the prevalence of hemosporidian parasites in seabirds. We discuss how these relationships should be further explored in future studies.

Prevalence of avian haematozoa in wild birds in a high-altitude forest in Japan

The infection dynamics of avian haematozoa, which includes the genera Plasmodium, Haemoproteus, and Leucocytozoon, are complicated by a variety of environmental factors and host-parasite interactions. In Japan, the prevalence of haematozoa in wild birds has recently been determined in several local areas. However, no information on the annual prevalence of avian haematozoa in a single study site has been reported. Here, we investigated the long-term infection dynamics of haematozoa in wild birds inhabiting a mountain forest of Japan. Blood samples were collected from 415 wild birds captured in the Chichibu mountains in Saitama Prefecture at an altitude of 1650 m between 2007 and 2010. All obtained samples were examined for haematozoan infection using nested polymerase chain reaction (PCR) of the cytochrome b (cytb) genes of haematozoa. A total of 62 out of 415 (14.9%) forest birds were PCR positive for haematozoa. Relatively high infection rates of Leucocytozoon were found among several bird species (Parus ater, 64.3%; Parus montanus, 81.8%) and may be due to the host preference of vector black flies and host nestling pattern in this forest. Phylogenetic analysis of amplified cytb sequences revealed for the first time that a variety of lineages of avian haematozoa are distributed among wild bird hosts in a high-altitude forest stand in Japan. Notably, significant seasonal changes of the prevalence of avian haematozoa were not observed; however, continuous investigation will likely provide detailed information on host-parasite interactions, including local environmental factors, that influence the dynamics of avian haematozoan infections.

Migratory divides and their consequences for dispersal, population size and parasite-host interactions

Populations of migratory birds differ in their direction of migration with neighbouring populations often migrating in divergent directions separated by migratory divides. A total of 26% of 103 passerine bird species in Europe had migratory divides that were located disproportionately often along a longitudinal gradient in Central Europe, consistent with the assumption of a Quaternary glacial origin of such divides in the Iberian and Balkan peninsulas followed by recolonization. Given that studies have shown significant genetic differentiation and reduced gene flow across migratory divides, we hypothesized that an absence of migratory divides would result in elevated rates of gene flow and hence a reduced level of local adaptation. In a comparative study, species with migratory divides had larger population sizes and population densities and longer dispersal distances than species without migratory divides. Species with migratory divides tended to be habitat generalists. Bird species with migratory divides had higher richness of blood parasites and higher growth rates of Staphylococcus on their eggs during the incubation period. There was weaker cell-mediated immunity in adults and stronger cell lysis in species with migratory divides. These findings may suggest that migratory divides constitute barriers to dispersal with consequences for ecology and evolution of distributions, population sizes, habitats and parasite-host interactions. They also suggest that migratory divides may play a role in local adaptation in host-parasite interactions.

Applying a regional community concept to forest birds of eastern North America

The regional community concept embraces the idea that species interactions across large areas shape both the geographic/ecological distributions and the local abundances of populations. Within this framework, I analyzed the distribution and abundance of 79 species of land birds across 142 ca. 10-ha census plots from standardized breeding bird censuses in deciduous and mixed forests of eastern North America. To characterize the regional ecological space, plots were ordinated on the basis of species abundances. Within the regional community defined by these synthetic axes, the distribution and abundance of individual species did not appear to be shaped by competition or to reflect the adaptations of individuals: (i) local abundance and population extent across the ordination axes were unrelated, (ii) pairwise correlation coefficients of species abundances were centered on 0, (iii) average species distribution and abundance were independent of the number of close relatives, and (iv) distribution and abundance exhibited no evolutionary (phylogenetic) conservatism. To explain these seemingly random patterns, I speculate that species are approximately evenly matched competitors over much of the region and that their distributions and relative abundances are determined by the labile coevolutionary outcomes of interactions with specialized pathogens. Thus, despite the appearance that random processes determine patterns in the distribution and abundance of populations in the regional community, it is plausible that species-specific deterministic interactions are responsible. Although competition is a dominant force in ecological communities, variation in the distribution and abundance of individual species might instead reflect the outcome of interactions with specialized antagonists, including pathogens.

Nonspecific patterns of vector, host and avian malaria parasite associations in a central African rainforest

Malaria parasites use vertebrate hosts for asexual multiplication and Culicidae mosquitoes for sexual and asexual development, yet the literature on avian malaria remains biased towards examining the asexual stages of the life cycle in birds. To fully understand parasite evolution and mechanism of malaria transmission, knowledge of all three components of the vector-host-parasite system is essential. Little is known about avian parasite-vector associations in African rainforests where numerous species of birds are infected with avian haemosporidians of the genera Plasmodium and Haemoproteus. Here we applied high resolution melt qPCR-based techniques and nested PCR to examine the occurrence and diversity of mitochondrial cytochrome b gene sequences of haemosporidian parasites in wild-caught mosquitoes sampled across 12 sites in Cameroon. In all, 3134 mosquitoes representing 27 species were screened. Mosquitoes belonging to four genera (Aedes, Coquillettidia, Culex and Mansonia) were infected with twenty-two parasite lineages (18 Plasmodium spp. and 4 Haemoproteus spp.). Presence of Plasmodium sporozoites in salivary glands of Coquillettidia aurites further established these mosquitoes as likely vectors. Occurrence of parasite lineages differed significantly among genera, as well as their probability of being infected with malaria across species and sites. Approximately one-third of these lineages were previously detected in other avian host species from the region, indicating that vertebrate host sharing is a common feature and that avian Plasmodium spp. vector breadth does not always accompany vertebrate-host breadth. This study suggests extensive invertebrate host shifts in mosquito-parasite interactions and that avian Plasmodium species are most likely not tightly coevolved with vector species.

Hemosporidian blood parasites in seabirds--a comparative genetic study of species from Antarctic to tropical habitats

Whereas some bird species are heavily affected by blood parasites in the wild, others reportedly are not. Seabirds, in particular, are often free from blood parasites, even in the presence of potential vectors. By means of polymerase chain reaction, we amplified a DNA fragment from the cytochrome b gene to detect parasites of the genera Plasmodium, Leucocytozoon, and Haemoproteus in 14 seabird species, ranging from Antarctica to the tropical Indian Ocean. We did not detect parasites in 11 of these species, including one Antarctic, four subantarctic, two temperate, and four tropical species. On the other hand, two subantarctic species, thin-billed prions Pachyptila belcheri and dolphin gulls Larus scoresbii, were found infected. One of 28 thin-billed prions had a Plasmodium infection whose DNA sequence was identical to lineage P22 of Plasmodium relictum, and one of 20 dolphin gulls was infected with a Haemoproteus lineage which appears phylogenetically clustered with parasites species isolated from passeriform birds such as Haemoproteus lanii, Haemoproteus magnus, Haemoproteus fringillae, Haemoproteus sylvae, Haemoproteus payevskyi, and Haemoproteus belopolskyi. In addition, we found a high parasite prevalence in a single tropical species, the Christmas Island frigatebird Fregata andrewsi, where 56% of sampled adults were infected with Haemoproteus. The latter formed a monophyletic group that includes a Haemoproteus line from Eastern Asian black-tailed gulls Larus crassirostris. Our results are in agreement with those showing that (a) seabirds are poor in hemosporidians and (b) latitude could be a determining factor to predict the presence of hemosporidians in birds. However, further studies should explore the relative importance of extrinsic and intrinsic factors on parasite prevalence, in particular using phylogenetically controlled comparative analyses, systematic sampling and screening of vectors, and within-species comparisons.

The impact of concomitant infections by Trypanosoma cruzi and intestinal helminths on the health of wild golden and golden-headed lion tamarins

A 4-year longitudinal epidemiological study was carried out to evaluate the effect of infection by Trypanosoma cruzi and three intestinal helminth species on the health of golden and golden-headed lion tamarins. We evaluated health using analysis of blood counts, serum proteins, electrophoretograms, electrocardiograms and a health ranking based on physiological parameters. Among the helminths, Trichostrongylidae was demonstrated as the most pathogenic, followed by Prosthenorchis sp.; concomitant infection by Spiruridae may exacerbate the negative effects of the other two helminths. T. cruzi infection was not highly detrimental to the health of the study animals and was correlated with increased resilience to helminths. Tamarins younger than 1-year of age or older than 4-years had lower health condition. Golden-headed lion tamarins were in lower health condition because of higher parasitic prevalence. Our data suggest that when parasite community pathogenicity and prevalence are high, natural selection will allow survival only of lion tamarins in the best health condition.

Evolutionary diversification, coevolution between populations and their antagonists, and the filling of niche space

The population component of a species' niche corresponds to the distribution of individuals across environments within a region. As evolutionary clades of species diversify, they presumably fill niche space, and, consequently, the rate of increase in species numbers slows. Total niche space and species numbers appear to be relatively stable over long periods, and so an increase in the species richness of one clade must be balanced by decrease in others. However, in several analyses, the total population niche space occupied per clade is independent of the number of species, suggesting that species in more diverse clades overlap more in niche space. This overlap appears to be accommodated by variation in the populations of each species, including their absence, within suitable niche space. I suggest that the uneven filling of niche space results from localized outcomes of the dynamic coevolutionary interactions of populations with their pathogens or other antagonists. Furthermore, I speculate that relationships with pathogens might constrain diversification if pathogen diversity increased with host diversity and resulted in more frequent host switching and emergent disease. Many indirect observations are consistent with these scenarios. However, the postulated influence of pathogens on the filling of niche space and diversification of clades primarily highlights our lack of knowledge concerning the space and time dimensions of coevolutionary interactions and their influence on population distribution and species diversification.

Blood parasitaemia in a high latitude flexible breeder, the white-winged crossbill,Loxia leucoptera: contribution of seasonal relapse versus new inoculations

We measured seasonal changes in the prevalence of haematozoa (Leucocytozoon fringillinarum, Haemoproteus fringillae, andTrypanosoma avium) in free-ranging White-winged Crossbills,Loxia leucoptera, over 1·5 year in Fairbanks, Alaska, USA. This prevalence was low during early winter.L. fringillinarumprevalence increased in late winter/early spring, in the absence of vectors, suggesting relapse of latent infection. By contrast, the prevalence ofT. aviumandH. fringillaedid not increase until mid-spring, coincident with the emergence of putative vectors and suggestive of new inoculations. The winter breeding period was not associated with lower body condition or elevated blood heterophil/lymphocyte ratios than the summer post-breeding period. Thus, birds unlikely perceived their breeding effort as particularly stressful. Adult males in May and June had low plasma testosterone and their blood prevalence ofL. fringillinarum, but not other haemoparasites, was higher than in adult females. This difference may have resulted from sex differences in behaviour and/or plumage colouration – bright red in males, dull green/yellow in females. Species in which reproduction and vector abundance are seasonally dissociated may constitute important models for investigating the respective contribution of reproductive hormones, breeding effort, and vector abundance to patent and latent hemoparasitic infections and to new inoculations.

Reduced parasite infestation in urban Eurasian blackbirds (Turdus merula): a factor favoring urbanization?

Humans nowadays dramatically alter environmental and ecological conditions worldwide. One of the most extreme forms of anthropogenic land-use alteration is urbanization. Animals thriving in urban areas are not only exposed to different environmental conditions compared with their nonurban conspecifics, but prevalence and impacts of wildlife diseases on urban populations may also be affected. In the present study, we tested whether blood-parasite prevalence differs between urban and forest habitats by comparing haematozoan infections of urban and forest-living Eurasian blackbirds ( Turdus merula L., 1758). In total, 76% of Eurasian blackbirds were infected with haematozoa and we detected five different blood parasite genera in both habitats. Blood-parasite prevalence varied both between years and between spring and summer in both urban and forest populations. Forest blackbirds had more parasite genera per individual than urban blackbirds, and in summer, forest blackbirds had higher blood-parasite prevalence than their urban conspecifics. These differences in blood-parasite prevalence between urban and forest blackbirds suggest a lower risk of haematozoan infections in urban than in forest habitats. The lower parasite prevalence could be one of the factors favoring the invasion of urban ecosystems.

Blood parasites in owls with conservation implications for the Spotted Owl (Strix occidentalis)

The three subspecies of Spotted Owl (Northern, Strix occidentalis caurina; California, S. o. occidentalis; and Mexican, S. o. lucida) are all threatened by habitat loss and range expansion of the Barred Owl (S. varia). An unaddressed threat is whether Barred Owls could be a source of novel strains of disease such as avian malaria (Plasmodium spp.) or other blood parasites potentially harmful for Spotted Owls. Although Barred Owls commonly harbor Plasmodium infections, these parasites have not been documented in the Spotted Owl. We screened 111 Spotted Owls, 44 Barred Owls, and 387 owls of nine other species for haemosporidian parasites (Leucocytozoon, Plasmodium, and Haemoproteus spp.). California Spotted Owls had the greatest number of simultaneous multi-species infections (44%). Additionally, sequencing results revealed that the Northern and California Spotted Owl subspecies together had the highest number of Leucocytozoon parasite lineages (n = 17) and unique lineages (n = 12). This high level of sequence diversity is significant because only one Leucocytozoon species (L. danilewskyi) has been accepted as valid among all owls, suggesting that L. danilewskyi is a cryptic species. Furthermore, a Plasmodium parasite was documented in a Northern Spotted Owl for the first time. West Coast Barred Owls had a lower prevalence of infection (15%) when compared to sympatric Spotted Owls (S. o. caurina 52%, S. o. occidentalis 79%) and Barred Owls from the historic range (61%). Consequently, Barred Owls on the West Coast may have a competitive advantage over the potentially immune compromised Spotted Owls.

Bird hosts, blood parasites and their vectors--associations uncovered by molecular analyses of blackfly blood meals

The level of host specificity of blood-sucking invertebrates may have both ecological and evolutionary implications for the parasites they are transmitting. We used blood meals from wild-caught blackflies for molecular identification of parasites and hosts to examine patterns of host specificity and how these may affect the transmission of avian blood parasites of the genus Leucocytozoon. We found that five different species of ornithophilic blackflies preferred different species of birds when taking their blood meals. Of the blackflies that contained avian blood meals, 62% were infected with Leucocytozoon parasites, consisting of 15 different parasite lineages. For the blackfly species, there was a significant association between the host width (measured as the genetic differentiation between the used hosts) and the genetic similarity of the parasites in their blood meals. The absence of similar parasite in blood meals from blackflies with different host preferences is interpreted as a result of the vector-host associations. The observed associations between blackfly species and host species are therefore likely to hinder parasites to be transmitted between different host-groups, resulting in ecologically driven associations between certain parasite lineages and hosts species.

Dynamics of parasitemia of malaria parasites in a naturally and experimentally infected migratory songbird, the great reed warbler Acrocephalus arundinaceus

Little is known about the development of infection of malaria parasites of the genus Plasmodium in wild birds. We used qPCR, targeting specific mitochondrial lineages of Plasmodium ashfordi (GRW2) and Plasmodium relictum (GRW4), to monitor changes in intensities of parasitemia in captive great reed warblers Acrocephalus arundinaceus from summer to spring. The study involved both naturally infected adults and experimentally infected juveniles. The experiment demonstrated that P. ashfordi and P. relictum lineages differ substantially in several life-history traits (e.g. prepatent period and dynamics of parasitemia) and that individual hosts show substantial differences in responses to these infections. The intensity of parasitemia of lineages in mixed infections co-varied positively, suggesting a control mechanism by the host that is general across the parasite lineages. The intensity of parasitemia for individual hosts was highly repeatable suggesting variation between the host individuals in their genetic or acquired control of the infections. In future studies, care must be taken to avoid mixed infections in wild caught donors, and when possible use mosquitoes for the experiments as inoculation of infectious blood ignores important initial stages of the contact between the bird and the parasite.

Prevalence of avian influenza and host ecology

Waterfowl and shorebirds are common reservoirs of the low pathogenic subtypes of avian influenza (LPAI), which are easily transmitted to poultry and become highly pathogenic. As the risk of virus transmission depends on the prevalence of LPAI in host-reservoir systems, there is an urgent need for understanding how host ecology, life history and behaviour can affect virus prevalence in the wild. To test for the most important ecological correlates of LPAI virus prevalence at the interspecific level, we applied a comparative analysis by using quantitative data on 30 bird species. We controlled for similarity among species due to common descent, differences in study effort and for covariance among ecological variables. We found that LPAI prevalence is a species-specific attribute and is a consequence of virus susceptibility, as it was negatively associated with the relative size of the bursa of Fabricius, an estimate of juvenile immune function. Species that migrate long distances have elevated prevalence of LPAI independent of phylogeny and other confounding factors. There was also a positive interspecific relationship between the frequency of surface feeding and virus prevalence, but this was sensitive to phylogenetic relatedness of species. Feeding in marine habitats is apparently associated with lower virus prevalence, but the effect of water salinity is likely to be indirect and affected by phylogeny. Our results imply that virus transmission via surface waters and frequent intra- and interspecific contacts during long migration are the major risk factors of avian influenza in the wild. However, the link between exploitation of surface waters and LPAI prevalence appears to be weaker than previously thought. This is the first interspecific study that provides statistical evidence that host ecology, immunity and phylogeny have important consequence for virus prevalence.

History and Diversity: Explorations at the Intersection of Ecology and Evolution

Phylogenetic analysis provides an important tool for assessing the influence of historical and evolutionary processes on the structure of contemporary ecological systems. Patterns of diversity, for example, represent the regional buildup of species through immigration and diversification, their loss through extinction, and the sorting of species ecologically within the region. Colonization-extinction dynamics on islands can be inferred from lineage accumulation through time. Lineage branching within clades can be used to estimate rates of speciation and extinction. However, simulations of these processes show potential ambiguities in the interpretation of data. Clade size is unrelated to age in many studies, suggesting that speciation and extinction might be in long-term equilibrium and raising questions about unobserved past diversity. Among passerine birds and other groups, the size of similar-aged clades is positively related to the size of the region within which they have diversified, and it is greater in tropical than in temperate regions. There is no consensus on the causes of these patterns. Finally, the ecological interactions between populations within regions brings the timescale of species sorting and species production close to each other and emphasizes the important interaction of ecological and evolutionary processes in shaping ecological systems.

Detecting shifts of transmission areas in avian blood parasites: a phylogenetic approach

We investigated the degree of geographical shifts of transmission areas of vector-borne avian blood parasites (Plasmodium, Haemoproteus and Leucocytozoon) over ecological and evolutionary timescales. Of 259 different parasite lineages obtained from 5886 screened birds sampled in Europe and Africa, only two lineages were confirmed to have current transmission in resident bird species in both geographical areas. We used a phylogenetic approach to show that parasites belonging to the genera Haemoproteus and Leucocytozoon rarely change transmission area and that these parasites are restricted to one resident bird fauna over a long evolutionary time span and are not freely spread between the continents with the help of migratory birds. Lineages of the genus Plasmodium seem more freely spread between the continents. We suggest that such a reduced transmission barrier of Plasmodium parasites is caused by their higher tendency to infect migratory bird species, which might facilitate shifting of transmission area. Although vector-borne parasites of these genera apparently can shift between a tropical and a temperate transmission area and these areas are linked with an immense amount of annual bird migration, our data suggest that novel introductions of these parasites into resident bird faunas are rather rare evolutionary events.

MALARIA AND RISK OF PREDATION: A COMPARATIVE STUDY OF BIRDS

Predators have been hypothesized to prey on individuals in a poor state of health, although this hypothesis has only rarely been examined. We used extensive data on prey abundance and availability from two long-term studies of the European Sparrowhawk (Accipiter nisus) and the Eurasian Goshawk (Accipiter gentilis) to quantify the relationship between predation risk of different prey species and infection with malaria and other protozoan blood parasites. Using a total of 31 745 prey individuals of 65 species of birds from 1709 nests during 1977-1997 for the Sparrowhawk and a total of 21 818 prey individuals of 76 species of birds from 1480 nests for the Goshawk during 1977-2004, we show that prey species with a high prevalence of blood parasites had higher risks of predation than species with a low prevalence. That was also the case when a number of confounding variables of prey species, such as body mass, breeding sociality, sexual dichromatism, and similarity among species in risk of predation due to common descent, were controlled in comparative analyses of standardized linear contrasts. Prevalence of the genera Haemoproteus, Leucocytozoon, Plasmodium, and Trypanosoma were correlated with each other, and we partitioned out the independent effects of different protozoan genera on predation risk in comparative analyses. Prevalence of Haemoproteus, Leucocytozoon, and Plasmodium accounted for interspecific variation in predation risk for the two raptors. These findings suggest that predation is an important factor affecting parasite-host dynamics because predators tend to prey on hosts that are more likely to be infected, thereby reducing the transmission success of parasites. Furthermore, this study demonstrates that protozoan infections are a common cause of death for hosts mediated by increased risk of predation.

Parasite-mediated heterozygote advantage in an outbred songbird population

Coevolution with parasites is thought to maintain genetic diversity in host populations. However, while there are sound theoretical reasons to expect heterozygosity and parasite resistance to be related, this pattern has generally been shown only in inbred laboratory and island populations. This leaves doubt as to whether parasite-mediated selection for genetic diversity is in fact a general process. Here we show that haematozoan parasite load is linked to two complementary measures of microsatellite variability in an outbred population of mountain white-crowned sparrows (Zonotrichia leucophrys oriantha) for which we know that parasites reduce fitness. Moreover, each of the genetic measures predicts a subtly different aspect of parasitism. Microsatellite heterozygosity is related to an individual's risk of parasitism, and mean d2 (a broader, more long-term measure of parental relatedness) to the severity of infection among parasitized individuals.

Temporal dynamics and diversity of avian malaria parasites in a single host species

1. We have used molecular methods to unravel a remarkable diversity of parasite lineages in a long-term population study of great reed warblers Acrocephalus arundinaceus that was not foreseen from traditional microscopic examination of blood smears. This diversity includes eight Haemoproteus and 10 Plasmodium lineages of which most probably represent good biological species. 2. Contrary to expectation, the relative frequency of parasite lineages seemed not to change over the 17-year study period and we found no effects of the parasites on a male secondary sexual ornament (song repertoire size) and two measures of fitness (adult survival and production of recruited offspring). 3. We discuss whether the absence of fitness consequences of the parasites might relate to the fact that we have studied the host at the breeding sites in Europe, whereas the transmission seems to take place at the wintering sites in Africa, where the naïve birds encounter the parasites for the first time and the resulting primary infections likely make them sicker than during the chronic phase of the infection. 4. The prevalence of the three most common lineages appeared to fluctuate in parallel with a periodicity of approximately 3-4 years. Theoretical models based on intrinsic interactions between parasite antigen and host immune genes cannot explain such dynamics, suggesting that knowledge of extrinsic parameters such as vector distribution and alternative hosts are required to understand these patterns.

Sensitive measure of prevalence and parasitaemia of haemosporidia from European blackbird (Turdus merula) populations: value of PCR-RFLP and quantitative PCR

Haemosporidian parasites are common in birds in which they act as an important selective pressure. While most studies so far have focused on the effect of their prevalence on host life-history traits, no study has measured the effect of parasitaemia. We developed molecular methods to detect, identify and quantify haemosporidia in 2 natural populations of the Blackbird Turdus merula. Three different parasite genotypes were found - 1 Haemoproteus and 2 Plasmodium. A PCR-RFLP screening revealed that only approximately 3% of blackbirds were free of parasites, compared to the 34% of uninfected birds estimated by blood smear screening. A quantitative PCR (q-PCR) assay revealed a weaker parasitaemia in microscopically undetected parasites compared to microscopically detected ones. Large parasitaemia differences were found between parasite species, suggesting either differing parasite life-histories or host resistance. Parasitaemias were also weaker in male hosts, and in urban habitats, suggesting that both host factors (e.g. immunity) and habitat characteristics (e.g. vector availability) may modulate parasite density. Interestingly, these differences in parasitaemia were comparable to differences in parasite prevalence estimated by smear screening. This suggests that previous results obtained by smear screening should be reinterpreted in terms of parasitaemia instead of parasite prevalence.