Age-specific haemosporidian infection dynamics and survival in Seychelles warblers

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.

Higher body condition with infection by Haemoproteus parasites in Bananaquits (Coereba flaveola)

Parasite transmission is a heterogenous process in host-parasite interactions. This heterogeneity is particularly apparent in vector-borne parasite transmission where the vector adds an additional level of complexity. Haemosporidian parasites, a widespread protist, cause a malaria-like disease in birds globally, but we still have much to learn about the consequences of infection to hosts' health. In the Caribbean, where malarial parasites are endemic, studying host-parasites interactions may give us important insights about energetic trade-offs involved in malarial parasites infections in birds. In this study, we tested the consequences of Haemoproteus infection on the Bananaquit, a resident species of Puerto Rico. We also tested for potential sources of individual heterogeneity in the consequences of infection such as host age and sex. To quantify the consequences of infection to hosts' health we compared three complementary body condition indices between infected and uninfected individuals. Our results showed that Bananaquits infected by Haemoproteus had higher body condition than uninfected individuals. This result was consistent among the three body condition indices. Still, we found no clear evidence that this effect was mediated by host age or sex. We discuss a set of non-mutually exclusive hypotheses that may explain this pattern including metabolic syndrome, immunological responses leading to host tolerance or resistance to infection, and potential changes in consumption rates. Overall, our results suggest that other mechanisms, may drive the consequences of avian malarial infection.

Natural Vector of Avian Haemoproteus asymmetricus Parasite and Factors Altering the Spread of Infection

Avian haemosporidians (Apicomplexa, Haemosporida) are widespread blood protists, often causing severe haemosporidiosis, pathology, or even mortality in their hosts. Migrant birds regularly bring various haemosporidian parasites from wintering grounds to European breeding areas. Some haemosporidian parasites are prevalent in breeding sites and complete their life cycles in temperate climate zones and can be transmitted, but others do not. The factors altering the spread of these haemosporidians are not fully understood. Culicoides biting midges (Diptera: Ceratopogonidae) play an important role in the transmission of worldwide distributed avian haemosporidian parasites belonging to the genus Haemoproteus, but this information is particularly scarce and insufficient. The key factors limiting the spread of these pathogens in temperate climate zones, which we suspect and aim to study, are the absence of susceptible vectors and the ecological isolation of birds from vectors during the breeding period when transmission occurs. The primary objective of this study was to evaluate how the habitats of biting midges and bird breeding sites influence parasite transmission while also seeking to expand our understanding of the natural vectors for these parasites. Biting midges were collected using UV traps on the Curonian Spit, Lithuania, in different habitats, such as woodland and reeds, from May to September. Parous Culicoides females were identified, dissected, and investigated for the presence of Haemoproteus parasites using both microscopy and PCR-based tools. Among the dissected 1135 parous Culicoides females, the sporozoites of Haemoproteus asymmetricus (genetic lineage hTUPHI01) have been detected for the first time in the salivary glands of Culicoides festivipennis. The sporozoites of four Haemoproteus lineages were detected in Culicoides segnis, C. festivipennis, and Culicoides kibunensis biting midges. PCR-based screening showed that the females of seven Culicoides species were naturally infected with Haemoproteus parasites. The DNA of the parasite of owls, Haemoproteus syrnii (hSTAL2), was detected for the first time in Culicoides punctatus. The highest abundance of collected Culicoides females was in June, but the highest prevalence of Haemoproteus parasites in biting midges was in July. The abundance of Culicoides was higher in the woodland compared with reeds during the season. The acquired findings indicate the varied abundance and diversity of biting midges throughout the season and across distinct habitats. This variability could potentially impact the transmission of Haemoproteus parasites among birds with diverse breeding site ecologies. These outcomes hold the potential to enhance our understanding of the epizootiology of Haemoproteus infections within temperate climatic zones.

Very low prevalence of haemosporidian parasites in two species of marsh terns

Vector-transmitted haemosporidians are among the most common parasites in birds, but our knowledge of the inter-specific patterns of infection rates and the parasite community composition is far from complete because of the unequal distribution of the screening effort across bird families and genera. To assess infection rates and the diversity of haemosporidians from the genera Plasmodium, Haemoproteus, and Leucocytozoon in marsh terns, which represent poorly explored in this regard genus of the family gulls, terns, and skimmers (Laridae), we screened two species: the Whiskered Tern (Chlidonias hybrida) and the Black Tern (Chlidonias niger). We sampled these long-distance migratory birds on breeding grounds: the Whiskered Tern in south-central Poland and north-central Ukraine, and the Black Tern-in north-central Ukraine. We found that birds from both species were infected only sporadically, with prevalence at the population level not exceeding 3.4%. Only parasites from the genera Plasmodium and Leucocytozoon were detected. There was neither an inter-specific difference nor a difference between populations of the Whiskered Tern in infection rates. In total, we registered three lineages-one Plasmodium and two Leucocytozoon-that were previously recorded in other bird species, and two unidentified Plasmodium infections. One of the lineages (Leucocytozoon LARCAC02) represents a specialist parasite with the host range restricted to larids and geographic range restricted to Poland, and two others (Plasmodium SGS1 and Leucocytozoon CIAE02) represent generalist parasites with very broad host and geographic ranges. This study reinforces the existing evidence that terns host parasites from genera Haemoproteus, Plasmodium, and Leucocytozoon only sporadically.

Host shift and natural long-distance dispersal to an oceanic island of a host-specific parasite

Parasite dispersal and host-switching may be better understood by knowing when they occurred. We estimated when the ancestor of a parasite of great reed warblers (Acrocephalus arundinaceus) dispersed to the Seychelles and began infecting the endemic Seychelles warbler (A. sechellensis). We used mitochondrial genomes and published molecular divergence rates to estimate the date of divergence between mitochondrial haplotypes of the parasite Haemoproteus nucleocondensis (lineage GRW01) in the great reed warbler and the Seychelles warbler. We also constructed a time-calibrated phylogeny of the hosts and their relatives to determine when the ancestor of the Seychelles warbler dispersed to the Seychelles. The two GRW01 lineages diverged ca 20-451 kya, long after the ancestor of the Seychelles warbler colonized the Seychelles ca 1.76-4.36 Mya. GRW01 rarely infects other species despite apparent opportunity. Humans were likely not involved in the dispersal of this parasite because humans settled the Seychelles long after the parasite diverged from its mainland relative. Furthermore, introduced birds are unlikely hosts of GRW01. Instead, the ancestor of GRW01 may have dispersed to the Seychelles with an errant migrating great reed warbler. Our results indicate that even specialized parasites can naturally disperse long distances to become emerging infectious diseases.

Causes and consequences of telomere lengthening in a wild vertebrate population

Telomeres have been advocated to be important markers of biological age in evolutionary and ecological studies. Telomeres usually shorten with age and shortening is frequently associated with environmental stressors and increased subsequent mortality. Telomere lengthening - an apparent increase in telomere length between repeated samples from the same individual - also occurs. However, the exact circumstances, and consequences, of telomere lengthening are poorly understood. Using longitudinal data from the Seychelles warbler (Acrocephalus sechellensis), we tested whether telomere lengthening - which occurs in adults of this species - is associated with specific stressors (reproductive effort, food availability, malarial infection and cooperative breeding) and predicts subsequent survival. In females, telomere shortening was observed under greater stress (i.e., low food availability, malaria infection), while telomere lengthening was observed in females experiencing lower stress (i.e., high food availability, assisted by helpers, without malaria). The telomere dynamics of males were not associated with the key stressors tested. These results indicate that, at least for females, telomere lengthening occurs in circumstances more conducive to self-maintenance. Importantly, both females and males with lengthened telomeres had improved subsequent survival relative to individuals that displayed unchanged, or shortened, telomeres - indicating that telomere lengthening is associated with individual fitness. These results demonstrate that telomere dynamics are bidirectionally responsive to the level of stress that an individual faces, but may poorly reflect the accumulation of stress over an individuals lifetime.

Haemosporidian parasites in the ash-breasted Sierra finch (Geospizopsis plebejus): insights from an Andean dry forest population

Haemosporidian genera Plasmodium, Haemoproteus and Leucocytozoon, responsible for avian malarial infections, are highly diverse and have a wide range of health effects and predictors, depending on the host and its environmental context. Here, we present, for the first time, detailed information on the identity, prevalence and parasitaemia of haemosporidians and other haemoparasites that infect the ash-breasted Sierra finch, Geospizopsis plebejus, in an Andean dry forest. We study the consequences of infection in the host body and health conditions and explore the environmental and intrinsic factors that influence infection status and parasitaemia. We conducted diagnoses by cytochrome b (cytb) sequencing and morphological identification, and estimated the levels of parasitaemia based on microscopy. We identified 6 cytb lineages infecting G. plebejus. Two of them were new lineages: Haemoproteus sp. GEPLE01 and GEPLE02. We also detected Haemoproteus sp. ZOCAP08, Haemoproteus sp. AMAVIR01, Plasmodium homopolare BAEBIC02 and Plasmodium cathemerium ZONCAP15. By microscopy, we detected Haemoproteus coatneyi, Haemoproteus erythrogravidus, P. homopolare and other unidentified species of Haemoproteus, Plasmodium, Babesia sp. and 1 microfilaria. We found no evidence of Leucocytozoon. Additionally, we detected several coinfections by sequencing and microscopy. The prevalence of haemosporidian infections was high (87.7%), and the mean parasitaemia was 61.65 infected cells per 10 000 erythrocytes examined. Prevalence and parasitaemia were higher for Haemoproteus than for Plasmodium. Haemoproteus sp. AMAVIR01 showed the highest prevalence (43.1%) and mean parasitaemia (94.39/10 000 erythrocytes) and might be associated with H. coatneyi. Immature individuals showed a lower prevalence than adults, supporting previous findings.

Poxvirus infection in house finches (Haemorhous mexicanus): genome sequence analysis and patterns of infection in wild birds

Poxviruses (family: Poxviridae) infect many avian species, causing several disease outcomes, the most common of which are proliferative lesions on the legs, feet and/or head. Few avian studies of poxvirus to date have combined molecular and ecological analyses to obtain a more comprehensive understanding of the identity and distribution of the disease in a population. Here we describe patterns of poxvirus infection in an urban population of house finches (Haemorhous mexicanus) in Arizona (USA) and use high-throughput sequencing determine the genome sequence of the virus. We found that poxvirus prevalence, based on visual identification of pox lesions, was 7.2% (17 infected birds out of a total of 235 sampled) in our population during summer 2021. Disease severity was low; 14 of the 17 infected birds had a single small lesion on the skin overlaying the eye, leg and ear canal. All but two lesions were found on the feet; one bird had a lesion on the eye and the other in the ear opening. We also investigated possible temporal (i.e., date of capture) and biological correlates (e.g., age, sex, body condition, degree of infection with coccidian endoparasites) of poxvirus infection in urban-caught house finches during this time but found that none of these significantly correlated with poxvirus presence/absence. Two complete poxvirus genomes were determined from two infected birds. These genomes are ∼354,000 bp and share 99.7% similarity with each other, and 82% with a canarypox virus genome, the most closely related avipoxvirus. This novel finchpox virus is the first to be reported in house finches and has a similar genome organization to other avipoxviruses. This article is protected by copyright. All rights reserved.

Gut microbiome composition, not alpha diversity, is associated with survival in a natural vertebrate population

BACKGROUND

The vertebrate gut microbiome (GM) can vary substantially across individuals within the same natural population. Although there is evidence linking the GM to health in captive animals, very little is known about the consequences of GM variation for host fitness in the wild. Here, we explore the relationship between faecal microbiome diversity, body condition, and survival using data from the long-term study of a discrete natural population of the Seychelles warbler (Acrocephalus sechellensis) on Cousin Island. To our knowledge, this is the first time that GM differences associated with survival have been fully characterised for a natural vertebrate species, across multiple age groups and breeding seasons.

RESULTS

We identified substantial variation in GM community structure among sampled individuals, which was partially explained by breeding season (5% of the variance), and host age class (up to 1% of the variance). We also identified significant differences in GM community membership between adult birds that survived, versus those that had died by the following breeding season. Individuals that died carried increased abundances of taxa that are known to be opportunistic pathogens, including several ASVs in the genus Mycobacterium. However, there was no association between GM alpha diversity (the diversity of bacterial taxa within a sample) and survival to the next breeding season, or with individual body condition. Additionally, we found no association between GM community membership and individual body condition.

CONCLUSIONS

These results demonstrate that components of the vertebrate GM can be associated with host fitness in the wild. However, further research is needed to establish whether changes in bacterial abundance contribute to, or are only correlated with, differential survival; this will add to our understanding of the importance of the GM in the evolution of host species living in natural populations.

The importance of considering age when quantifying wild animals' welfare

Wild animals experience different challenges and opportunities as they mature, and this variety of experiences can lead to different levels of welfare characterizing the day-to-day lives of individuals of different ages. At the same time, most wild animals who are born do not survive to adulthood. Individuals who die as juveniles do not simply experience a homogeneous fraction of the lifetimes of older members of their species; rather, their truncated lives may be characterized by very different levels of welfare. Here, I propose the concept of welfare expectancy as a framework for quantifying wild animal welfare at a population level, given individual-level data on average welfare with respect to age. This concept fits conveniently alongside methods of analysis already used in population ecology, such as demographic sensitivity analysis, and is applicable to evaluating the welfare consequences of human interventions and natural pressures that disproportionately affect individuals of different ages. In order to understand better and improve the state of wild animal welfare, more attention should be directed towards young animals and the particular challenges they face.

Contemporary evolution of the innate immune receptor gene TLR3 in an isolated vertebrate population

Understanding where genetic variation exists, and how it influences fitness within populations is important from an evolutionary and conservation perspective. Signatures of past selection suggest that pathogen-mediated balancing selection is a key driver of immunogenetic variation, but studies tracking contemporary evolution are needed to help resolve the evolutionary forces and mechanism at play. Previous work in a bottlenecked population of Seychelles warblers (Acrocephalus sechellensis) show that functional variation has been maintained at the viral-sensing Toll-like receptor 3 (TLR3) gene, including one nonsynonymous SNP, resulting in two alleles. Here, we characterise evolution at this TLR3 locus over a 25-year period within the original remnant population of the Seychelles warbler, and in four other derived, populations. Results show a significant and consistent temporal decline in the frequency of the TLR3^C allele in the original population, and that similar declines in the TLR3^C allele frequency occurred in all the derived populations. Individuals (of both sexes) with the TLR3^CC genotype had lower survival, and males - but not females - that carry the TLR3^C allele had significantly lower lifetime reproductive success than those with only the TLR3^A allele. These results indicate that positive selection on the TLR3^A allele, caused by an as yet unknown agent, is driving TLR3 evolution in the Seychelles warbler. No evidence of heterozygote advantage was detected. However, whether the positive selection observed is part of a longer-term pattern of balancing selection (through fluctuating selection or rare-allele advantage) cannot be resolved without tracking the TLR3^C allele over an extended time period.

Sex and nest type influence avian blood parasite prevalence in a high-elevation bird community

Background

The prevalence of avian haemosporidian parasites and the factors influencing infection in the Colorado Rocky Mountains are largely unknown. With climate change expected to promote the expansion of vector and avian blood parasite distributions, baseline knowledge and continued monitoring of the prevalence and diversity of these parasites is needed.

Methods

Using an occupancy modeling framework, we conducted a survey of haemosporidian parasite species infecting an avian community in the Colorado Rocky Mountains in order to estimate the prevalence and diversity of blood parasites and to investigate species-level and individual-level characteristics that may influence infection.

Results

We estimated the prevalence and diversity of avian Haemosporidia across 24 bird species, detecting 39 parasite haplotypes. We found that open-cup nesters have higher Haemoproteus prevalence than cavity or ground nesters. Additionally, we found that male Ruby-crowned Kinglets, White-crowned Sparrows, and Wilson’s Warblers have higher Haemoproteus prevalence compared to other host species. Plasmodium prevalence was relatively low (5%), consistent with the idea that competent vectors may be rare at high altitudes.

Conclusions

Our study presents baseline knowledge of haemosporidian parasite presence, prevalence, and diversity among avian species in the Colorado Rocky Mountains and adds to our knowledge of host–parasite relationships of blood parasites and their avian hosts.

Hematocrit, age, and survival in a wild vertebrate population

Understanding trade-offs in wild populations is difficult, but important if we are to understand the evolution of life histories and the impact of ecological variables upon them. Markers that reflect physiological state and predict future survival would be of considerable benefit to unraveling such trade-offs and could provide insight into individual variation in senescence. However, currently used markers often yield inconsistent results. One underutilized measure is hematocrit, the proportion of blood comprising erythrocytes, which relates to the blood's oxygen-carrying capacity and viscosity, and to individual endurance. Hematocrit has been shown to decline with age in cross-sectional studies (which may be confounded by selective appearance/disappearance). However, few studies have tested whether hematocrit declines within individuals or whether low hematocrit impacts survival in wild taxa. Using longitudinal data from the Seychelles warbler (Acrocephalus sechellensis), we demonstrated that hematocrit increases with age in young individuals (<1.5 years) but decreases with age in older individuals (1.5-13 years). In breeders, hematocrit was higher in males than females and varied relative to breeding stage. High hematocrit was associated with lower survival in young individuals, but not older individuals. Thus, while we did not find support for hematocrit as a marker of senescence, high hematocrit is indicative of poor condition in younger individuals. Possible explanations are that these individuals were experiencing dehydration and/or high endurance demands prior to capture, which warrants further investigation. Our study demonstrates that hematocrit can be an informative metric for life-history studies investigating trade-offs between survival, longevity, and reproduction.

Effects of forest structure on the interaction between avian hosts, dipteran vectors and haemosporidian parasites

Background

Forest habitats are important biodiversity refuges for a wide variety of bird species. Parasitism may modulate host species presence and abundance, and parasite effects can change according to forest management practices. Such processes are not well studied in vector-borne avian haemosporidians. We analyzed the effects of forest management on bird-dipteran-haemosporidian interactions, using seven common bird species in managed and unmanaged beech forest habitats in northeastern Germany. We assumed that forest structural heterogeneity affects parasite population parameters in avian hosts (i.e., prevalence and parasitemia), through its effect on the condition of the avian host but also through varying vector abundances.

Results

Parasite prevalence was high (about 80%) and homogeneous across different beech forest categories (i.e., young, old, unmanaged) and for all bird species, except Erithacus rubecula (35%). Parasitemia varied across bird species but not across forest categories within each avian species (lowest parasitemia were found in E. rubecula, Turdus merula, and Turdus philomelos). In our study system, we found that vector abundance was not the main driver of parasite dynamics. We found that forest structure affects parasite infection probability directly and potentially host condition via available resources that have to be used either to combat infections (i.e., high parasitemia) or to maintain a good body condition.

Conclusions

The effects of each of the predictors were bird species-specific, and we found that Diptera vectors were not the foremost influence in our host-vector-parasite system. Effects of forest habitat variables indicated that for most bird species in this study, habitat regulation of infection probability was more likely (i.e., E. rubecula, Fringilla coelebs, Sylvia atricapilla), whereas for Parus major habitat characteristics impacted first individuals' body condition and subsequently the probability of infection. Our findings emphasize the need of species-specific analyses and to use continuous forest structural parameters (e.g., the proportion of gap, south facing aspect) to better understand habitat and land use effects on host-vector-parasite dynamics.

Age-Related Brood Parasitism and Egg Rejection in Magpie Hosts

When the strength or nature of a host-parasite interaction changes over the host life cycle, the consequences of parasitism can depend on host population age structure. Avian brood parasites reduce hosts' breeding success, and host age may play a role in this interaction if younger hosts are more likely parasitized and/or less able to defend themselves. We analyzed whether the age of female magpie (Pica pica) hosts is associated with parasite attack or their ability to reject foreign eggs. We recorded parasitism and model egg rejection of known-age individuals over their lifetime and established whether the likelihood of parasitism or egg rejection changed with age or longevity. Parasitism probability did not change with female age, and there was a trend toward longer-lived females being less likely to be parasitized. However, model egg rejection probability increased with age for each individual female, and longer-lived females were more prone to reject model eggs. Most females in the population were young, and the majority of them accepted model eggs, suggesting that brood parasites exploiting younger host individuals are benefitting from a lower defense level of their hosts. Our results stress that the intensity of selection by brood parasites may be mediated by the age structure of host populations, a to-date neglected aspect in brood parasite-host research.

Complete sporogony of the blood parasite Haemoproteus nucleocondensus in common biting midges: why is its transmission interrupted in Europe?

Haemoproteus species (Haemoproteidae) are widespread blood parasites and are transmitted by Culicoides biting midges and Hippoboscidae louse flies. Although these pathogens may cause morbidity or mortality, the vectors and patterns of transmission remain unknown for the great majority of avian haemoproteids. Haemoproteus nucleocondensus has been frequently reported in Europe in great reed warblers Acrocephalus arundinaceus after their arrival from African wintering grounds, but this infection has not been found in juveniles at the breeding sites. The factors that prevent its transmission remain unclear. This study was designed to test whether the sporogony of H. nucleocondensus (lineage hGRW8) can be completed in Culicoides impunctatus, one of the most abundant European biting midge species. Wild-caught females were infected with H. nucleocondensus from great reed warblers. Microscopic examination and PCR-based methods were used to detect sporogonic stages and to confirm species identity. This study showed that H. nucleocondensus completes sporogony in C. impunctatus, suggesting that there are no obstacles to its transmission from the point of view of vector availability and average temperature in Northern Europe. We discuss other ecological factors which should be considered to explain why the transmission of H. nucleocondensus and some other Southern origin haemosporidians are interrupted in North Europe.

Haemoproteus paraortalidum n. sp. in captive Black-fronted Piping-guans Aburria jacutinga (Galliformes, Cracidae): High prevalence in a population reintroduced into the wild

Haemosporidian parasites of the genus Haemoproteus are widespread and can cause disease and even mortality in birds under natural and captive conditions. The Black-fronted Piping-guan (Aburria jacutinga) is an endangered Neotropical bird of the Cracidae (Galliformes) going through a reintroduction program to avoid extinction. We used microscopic examination and partial cytochrome b DNA sequencing to describe a new Haemoproteus species infecting Black-fronted Piping-guans bred and raised in captivity that were reintroduced into the Atlantic rainforest. Haemoproteus (Parahaemoproteus) paraortalidum n. sp. was detected in the blood of 19 out of 29 examined birds. The new species is distinguished from other haemoproteids due to the shape of gametocytes, which have pointed ends in young stages, and due to the presence of vacuole-like unstained spaces in macrogametocytes and numerous volutin granules both in macro- and microgametocytes. Illustrations of the new species are provided. Phylogenetic inference positioned this parasite in the Parahaemoproteus subgenus clade together with the other two Haemoproteus genetic lineages detected in cracids up to date. We discuss possible implications of the reintroduction of birds infected with haemosporidian parasites into the wild. Treatment of Haemoproteus infections remains insufficiently studied, but should be considered for infected birds before reintroduction to improve host reproductive and survival rates after release.

Age and infection history are revealed by different ornaments in a warbler

Female preference for older or more disease-resistant males are both possible outcomes of parasite-mediated sexual selection, but the extent to which infection alters the development of ornaments to yield signals of male age and health has rarely been explored. In a longitudinal study of 61 male common yellowthroats (Geothlypis trichas), age-related increases in the size of the melanin-based mask and carotenoid-based bib were not correlated among young males, likely owing to differences in how blood parasites affect ornament development. Infection with trypanosomes and hemosporidians in a male's first breeding season was associated with slower growth of the mask; uninfected males attained large masks in their second breeding season, while infected males attained large masks in their third breeding season. In contrast, the bib size of males increased every year regardless of infection. As a consequence, different populations of males are identified by the largest ornaments-older males in the case of bib and a combination of older males and young, uninfected males in the case of mask. Although mask is thus the more informative trait with respect to male health, females prefer large bibs in our population. If infection is opportunistic, young, uninfected males may not possess good genes for parasite resistance but simply good luck, and it may benefit females to prefer older males who are more likely to have withstood prior episodes of selection. A "pure" signal of age may be a more reliable signal of resistance to parasites than an ornament whose expression is modulated by infection.

Links between blood parasites, blood chemistry, and the survival of nestling American crows

Many studies have used the avian hemosporidians (Leucocytozoon, Plasmodium, and Hemoproteus) to test hypotheses of host-parasite co-evolution, yet documented health and survival consequences of these blood parasites vary among studies and generalizations about their pathogenicity are debatable. In general, the negative effects of the hemosporidians are likely to be greatest during acute infections of young birds, yet most previous studies in wild passerines have examined chronic effects in adults. Here, we evaluated responses of nestling American crows (Corvus brachyrhynchos) to acute infection (prevalence and burden), as well as its short- and long-term survival consequences. We used panel of nine hematological and biochemical parameters that are regularly used to evaluate the health of domestic animals, including leukocyte profiles, hematocrit, and plasma proteins. We assessed the effects of infection on survival in a mark-recapture framework. Overall, 56% of crows (n = 321 samples) were infected by at least one of the three genera. Infections by all genera were associated with elevated plasma proteins and globulins, which could indicate an adaptive immune response. However, only Plasmodium infections were associated with low hematocrit (anemia) and lower fledging success, possibly mediated by the negative effect of low hematocrit values on body condition. Moreover, early Plasmodium infection (<40 days of age) had long-term survival implications: it was associated with lower apparent survival probability within 3 years after fledging. These results suggest that young crows mounted an adaptive immune response to all three genera. Short- and long-term pathological effects, however, were only apparent with Plasmodium infections.

Blood parasite infections in a wild population of ravens (Corvus corax) in Bulgaria

BACKGROUND

Blood parasites have been studied intensely in many families of avian hosts, but corvids, a particularly cosmopolitan family, remain underexplored. Haemosporidian parasites of the common raven (Corvus corax) have not been studied, although it is the largest, most adaptable, and widespread corvid. Genetic sequence data from parasites of ravens can enhance the understanding of speciation patterns and specificity of haemosporidian parasites in corvids, and shed light how these hosts cope with parasite pressure.

METHODS

A baited cage trap was used to catch 86 ravens and a nested PCR protocol was used to amplify a 479 bp fragment of the haemosporidian cytochrome b gene from the samples. The obtained sequences were compared with the MalAvi database of all published haemosporidian lineages and a phylogenetic tree including all detected raven parasites was constructed. An examination of blood smears was performed for assessment of infection intensity.

RESULTS

Twenty blood parasite lineages were recovered from ravens caught in a wild population in Bulgaria. The prevalence of generalist Plasmodium lineages was 49%, and the prevalence of Leucocytozoon lineages was 31%. Out of 13 detected Leucocytozoon lineages six were known from different corvids, while seven others seem to be specific to ravens. A phylogenetic reconstruction suggests that Leucocytozoon lineages of ravens and other corvids are not monophyletic, with some groups appearing closely related to parasites of other host families.

CONCLUSIONS

Several different, morphologically cryptic groups of Leucocytozoon parasites appear to infect corvids. Ravens harbour both generalist corvid Leucocytozoon as well as apparently species-specific lineages. The extraordinary breeding ecology and scavenging lifestyle possibly allow ravens to evade vectors and have relatively low blood parasite prevalence compared to other corvids.

Intra-individual changes in haemosporidian infections over the nesting period in great tit females

Prevalence of haemosporidian parasites in bird populations varies temporally both between years and within a year. In contrast to variation at the population level, relatively little is known about variation in infection attributes at the individual level, especially in non-migratory species. We examined intra-individual changes in the presence and identity of haemosporidian parasites (genera Plasmodium and Haemoproteus) over the course of the nesting period in females of great tits (Parus major)—a species considered to be resident over much of its distribution range. Birds were sampled during two stages of the nesting period: nest building and nestling rearing. The mean time interval between sampling occasions was 43 days. Between the first and second samplings, 30.6% of females gained at least one parasite lineage and 18.5% lost the lineage. Haemoproteus gains were over three times more common than Plasmodium gains. The probability of the lineage gain decreased with the date of the first sampling, was higher in individuals in better body condition and differed between years, but was not associated with the host age. The probability of the lineage loss was not explained by any of the considered parameters except for year. These results indicate that in a large proportion of a population, infection attributes (presence/absence and/or parasite identity) may change over the nesting period and the occurrence of such changes may be associated with the individual quality. Consequently, this phenomenon should be taken into account to correctly interpret parasite-mediated effects.