Diverse Host Species Research Articles

Cloaca‐ and feather‐associated bacteria communities in common waxbills Estrilda astrild

Host‐associated microbial communities are essential for host homeostasis and health. Most research on microbiotas is restricted to model host species and, since microbe–host dynamics can be species‐specific, we still lack a good taxonomic, ecological and evolutionary understanding of microbiotas in wild hosts, including birds. Given the diversity of avian host species, their habitat specializations, ecological requirements and life‐history traits, we need to characterize the dynamics of microbiotas from taxonomically diverse bird species. Here we describe cloaca and feather microbiotas of a population of common waxbills Estrilda astrild living in a large open‐air mesocosm, and compare it to microbiotas sampled one year later for a subset of this population, and to the microbiotas of free‐ranging waxbills from the same region. We found clear differences between microbiota from the cloaca, which contained some taxa that may be found in seeds, and from feathers, which contained some taxa that have been previously found in plants and soil. We found limited evidence for sexual differences in both cloaca and feather microbiotas, likely due to the gregariousness, similar behaviour and habitat use of both male and female waxbills. Microbial diversities of waxbills from the mesocosm were representative of those found in free‐ranging individuals. Also, structural differences between microbiota from mesocosm and free‐ranging waxbills seemed to be small and comparable to differences found in microbiota from the mesocosm in consecutive years. These results indicate that this mesocosm population could be used as a model in future studies investigating microbiota–host dynamics.

Scratching the Itch: Updated Perspectives on the Schistosomes Responsible for Swimmer's Itch around the World.

Although most studies of digenetic trematodes of the family Schistosomatidae dwell on representatives causing human schistosomiasis, the majority of the 130 identified species of schistosomes infect birds or non-human mammals. The cercariae of many of these species can cause swimmer’s itch when they penetrate human skin. Recent years have witnessed a dramatic increase in our understanding of schistosome diversity, now encompassing 17 genera with eight more lineages awaiting description. Collectively, schistosomes exploit 16 families of caenogastropod or heterobranch gastropod intermediate hosts. Basal lineages today are found in marine gastropods and birds, but subsequent diversification has largely taken place in freshwater, with some reversions to marine habitats. It seems increasingly likely that schistosomes have on two separate occasions colonized mammals. Swimmer’s itch is a complex zoonotic disease manifested through several different routes of transmission involving a diversity of different host species. Swimmer’s itch also exemplifies the value of adopting the One Health perspective in understanding disease transmission and abundance because the schistosomes involved have complex life cycles that interface with numerous species and abiotic components of their aquatic environments. Given the progress made in revealing their diversity and biology, and the wealth of questions posed by itch-causing schistosomes, they provide excellent models for implementation of long-term interdisciplinary studies focused on issues pertinent to disease ecology, the One Health paradigm, and the impacts of climate change, biological invasions and other environmental perturbations.

Diversity and Ecological Status of Major Lac Host Species in the Village Commons of the Periphery of Kuldiha Wildlife Sanctuary of Odisha

An ecological study was carried out in village commons of fringe forests (i.e. 05 Km) in the tropical deciduous forests of the periphery of Kuldiha Wildlife Sanctuary of Odisha during 2018-19. This paper has endeavoured to assess the diversity and distribution pattern of trees vis-à-vis major lac host species in the outer peripheral region of Kuldiha Wildlife Sanctuary in the Garadihi Gram Panchayat of Nilgiri Block, Balasore, Odisha. An attempt was made to present floral diversity in the study site and estimated diversity index using Simpson's Diversity Index were determined to draw a comparative inference. Stratified random samplings were laid in the field. A total of 44 tree species consisting of 31 genera and 17 families were recorded. Fabaceae was the most dominant family with 13 species. a major lac host Butea monosperma, species, recorded the highest tree density (120.00 individual's ha ) and the lowest tree density (10 individual's ha ) was observed for -1 -1Neolamarckia cadamba Ficus religiosa Shorea robusta and . had the highest basal area ha of 164.56. The Importance Value Index (IVI) of -1 trees was the highest for (20.74) followed by which was also a major lac host species (16.15) andShorea robusta Schleichera oleosa Holarrhena antidysenterica Neolamarckia cadamba (15.07 while the lowest was for (1.82). Species evenness for trees was (0.951). ) Abundance/ Frequency ratio (A/F) for trees of 44 species exhibited mostly random distribution patterns for 26 species, 13 species contagiously and 5 species were regularly distributed.

Histone Modification Landscapes as a Roadmap for Malaria Parasite Development.

Plasmodium falciparum remains the deadliest parasite species in the world, responsible for 229 million cases of human malaria in 2019. The ability of the P. falciparum parasite to progress through multiple life cycle stages and thrive in diverse host and vector species hinges on sophisticated mechanisms of epigenetic regulation of gene expression. Emerging evidence indicates such epigenetic control exists in concentric layers, revolving around core histone post-translational modification (PTM) landscapes. Here, we provide a necessary update of recent epigenome research in malaria parasites, focusing specifically on the ability of dynamic histone PTM landscapes to orchestrate the divergent development and differentiation pathways in P. falciparum parasites. In addition to individual histone PTMs, we discuss recent findings that imply functional importance for combinatorial PTMs in P. falciparum parasites, representing an operational histone code. Finally, this review highlights the remaining gaps and provides strategies to address these to obtain a more thorough understanding of the histone modification landscapes that are at the center of epigenetic regulation in human malaria parasites.

An overview of Lepidoptera-host-parasitoid associations for southern Africa, including an illustrated report on 2 370 African Lepidoptera-host and 119 parasitoid-Lepidoptera associations

We present an overview of the known host associations of larval Lepidoptera for southern Africa, based on a database of 11 628 rearings, including all Caterpillar Rearing Group (CRG) records and other published records. Rearings per Lepidoptera family show some bias in the rearing effort towards the more conspicuous families, ectophagous groups and non-detritus-feeders but in general follow species diversity. Recorded Lepidoptera host associations per host family for southern Africa are shown. Data analyses revealed the following general trends: of the 20 most reared species 13 are polyphagous; Fabaceae are the most utilised plant family with 2 122 associations, followed by Asteraceae (600), Malvaceae (564) and Anacardiaceae (476); 98.8 % of hosts are vascular plants; and of the 19 most utilised host species 18 are common trees or shrubs. We discuss possible reasons behind these trends, particularly the high utilisation of Fabaceae and the widespread use of trees and shrubs as hosts. We compare recorded host species numbers with species diversity for the 19 most recorded host families and discuss possible reasons for the low utilisation of four plant families with an exceptionally low percentage of Lepidoptera host species / plant host species diversity. All Lepidoptera families for which more than 100 rearings have been recorded (21 families) utilise one (or two in the case of Pyralidae, Nolidae and Hesperiidae) plant family exponentially more than any of the other families, with resulting histograms forming hyperbolic curves, as are typical of distributions of taxonomic assemblages in nature. We calculate an exponential factor to quantify this phenomenon and show that for all 21 Lepidoptera families one host family is utilised 6–33 times more than the average use of other host families. In this paper, the larvae and adults of 953 African, mostly South African, Lepidoptera species reared by the CRG between January 2016 and June 2019 are illustrated together with pertinent host information. 119 Lepidoptera-parasitoid associations are reported, comprising seven hymenopteran families and one dipteran family. With the current data release, larval host association records are now available for 2 826 Lepidoptera species in the southern African subregion, covering about 25 % of the described fauna.

Deep sequencing across multiple host species tests pine-endophyte specificity.

Foliar fungal endophytes vary in their distributions across landscapes or plant host taxa, indicative of specialized ecologies and host specific adaptations. Accounts of specialization, however, depend on the taxonomic breadth and geographic range of the host plants included in each study. A broad region-scale study or deep sampling of diverse potential host species still remains relatively rare but is becoming increasingly possible with high-throughput sequencing. Amplicon sequencing was used to rapidly identify the fungal endophytic community among six pine (Pinus, Pinaceae) species co-occurring across northeastern United States and to test for site and host specialization. We focused on the endophytic genus Lophodermium (Rhytismataceae), whose species members are thought to specialize on different pine species, to test if amplicon sequencing could rapidly verify previously implied or discover new patterns of host specificity. While amplicon sequencing could analyze more samples at greater depths and recover greater numbers of unique Lophodermium taxa than when endophyte communities were surveyed with traditional culturing methods, patterns of specialization were not better supported. This may be because amplicon sequencing can indiscriminately capture non-host specific organisms found incidentally from plant tissues or because we have overestimated host-specificity in the past with biased culturing techniques. Amplicon sequencing can quickly identify patterns of host specificity by allowing large-scale surveys but has limitations in quantifying the level of intimacy of these relationships.

Tracking the amino acid changes of spike proteins across diverse host species of severe acute respiratory syndrome coronavirus 2

SummaryKnowledge of the host-specific properties of the spike protein is of crucial importance to understand the adaptability of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) to infect multiple species and alter transmissibility, particularly in humans. Here, we propose a spike protein predictor SPIKES incorporating with an inheritable bi-objective combinatorial genetic algorithm to identify the biochemical properties of spike proteins and determine their specificity to human hosts. SPIKES identified 20 informative physicochemical properties of the spike protein, including information measures for alpha helix and relative mutability, and amino acid and dipeptide compositions, which have shown compositional difference at the amino acid sequence level between human and diverse animal coronaviruses. We suggest that alterations of these amino acids between human and animal coronaviruses may provide insights into the development and transmission of SARS-CoV-2 in human and other species and support the discovery of targeted antiviral therapies.

Host Identity and Geographic Location Significantly Affect Gastrointestinal Microbial Richness and Diversity in Western Lowland Gorillas (Gorilla gorilla gorilla) under Human Care.

Simple SummarySince the advent of microbiome research, this field has seen an explosion of both techniques and subfields. Researchers have aimed not only to classify microbiome membership and diversity among varying hosts, but to also identify and understand new and novel microbial lineages. This wealth of knowledge continues to grow, and with it the potential to use microbiome databases as diagnostic tools. This diagnostic application is of great importance and interest in zoological settings, as it may provide a non-invasive assessment of animal health. However, before this tool can be utilized in zoos, more data are needed to assess the extent of microbial variation characteristics to each host species to know what may be problematic versus normal. The aim of this research was to characterize variation of the microbiome at the individual level within managed populations of western lowland gorillas in three zoological institutions.The last few decades have seen an outpouring of gastrointestinal (GI) microbiome studies across diverse host species. Studies have ranged from assessments of GI microbial richness and diversity to classification of novel microbial lineages. Assessments of the “normal” state of the GI microbiome composition across multiple host species has gained increasing importance for distinguishing healthy versus diseased states. This study aimed to determine baselines and trends over time to establish “typical” patterns of GI microbial richness and diversity, as well as inter-individual variation, in three populations of western lowland gorillas (Gorilla gorilla gorilla) under human care at three zoological institutions in North America. Fecal samples were collected from 19 western lowland gorillas every two weeks for seven months (n = 248). Host identity and host institution significantly affected GI microbiome community composition (p < 0.05), although host identity had the most consistent and significant effect on richness (p = 0.03) and Shannon diversity (p = 0.004) across institutions. Significant changes in microbial abundance over time were observed only at Denver Zoo (p < 0.05). Our results suggest that individuality contributes to most of the observed GI microbiome variation in the study populations. Our results also showed no significant changes in any individual’s microbial richness or Shannon diversity during the 7-month study period. While some microbial taxa (Prevotella, Prevotellaceae and Ruminococcaceae) were detected in all gorillas at varying levels, determining individual baselines for microbial composition comparisons may be the most useful diagnostic tool for optimizing non-human primate health under human care.

Genetic diversity of Pasteurella multocida isolates of Indian origin

In the current study, correlation among specific capsular types, sequence types and specific hosts were observed. Study proves high diversity with respect to small ruminant isolates belonging to capsular type A. Higher sharing of sequence types among small ruminant, porcine and avian hosts indicate the close association of these isolates getting adapted for diverse host species. The study also shows that CC229, mostly from small ruminant hosts, was genetically related to HS-specific ST122 indicating recent diversification and possibly, similar genotype and pathogenesis.

Unexpected myriad of co-occurring viral strains and species in one of the most abundant and microdiverse viruses on Earth.

Viral genetic microdiversity drives adaptation, pathogenicity, and speciation and has critical consequences for the viral-host arms race occurring at the strain and species levels, which ultimately impact microbial community structure and biogeochemical cycles. Despite the fact that most efforts have focused on viral macrodiversity, little is known about the microdiversity of ecologically important viruses on Earth. Recently, single-virus genomics discovered the putatively most abundant ocean virus in temperate and tropical waters: the uncultured dsDNA virus vSAG 37-F6 infecting Pelagibacter, the most abundant marine bacteria. In this study, we report the cooccurrence of up to ≈1,500 different viral strains (>95% nucleotide identity) and ≈30 related species (80-95% nucleotide identity) in a single oceanic sample. Viral microdiversity was maintained over space and time, and most alleles were the result of synonymous mutations without any apparent adaptive benefits to cope with host translation codon bias and efficiency. Gene flow analysis used to delimitate species according to the biological species concept (BSC) revealed the impact of recombination in shaping vSAG 37-F6 virus and Pelagibacter speciation. Data demonstrated that this large viral microdiversity somehow mirrors the host species diversity since ≈50% of the 926 analyzed Pelagibacter genomes were found to belong to independent BSC species that do not significantly engage in gene flow with one another. The host range of this evolutionarily successful virus revealed that a single viral species can infect multiple Pelagibacter BSC species, indicating that this virus crosses not only formal BSC barriers but also biomes since viral ancestors are found in freshwater.

Positive Selection and Horizontal Gene Transfer in the Genome of a Male-Killing Wolbachia.

Wolbachia are a genus of widespread bacterial endosymbionts in which some strains can hijack or manipulate arthropod host reproduction. Male killing is one such manipulation in which these maternally transmitted bacteria benefit surviving daughters in part by removing competition with the sons for scarce resources. Despite previous findings of interesting genome features of microbial sex ratio distorters, the population genomics of male-killers remain largely uncharacterized. Here, we uncover several unique features of the genome and population genomics of four Arizonan populations of a male-killing Wolbachia strain, wInn, that infects mushroom-feeding Drosophila innubila. We first compared the wInn genome with other closely related Wolbachia genomes of Drosophila hosts in terms of genome content and confirm that the wInn genome is largely similar in overall gene content to the wMel strain infecting D. melanogaster. However, it also contains many unique genes and repetitive genetic elements that indicate lateral gene transfers between wInn and non-Drosophila eukaryotes. We also find that, in line with literature precedent, genes in the Wolbachia prophage and Octomom regions are under positive selection. Of all the genes under positive selection, many also show evidence of recent horizontal transfer among Wolbachia symbiont genomes. These dynamics of selection and horizontal gene transfer across the genomes of several Wolbachia strains and diverse host species may be important underlying factors in Wolbachia’s success as a male-killer of divergent host species.

A field test of the dilution effect hypothesis in four avian multi-host pathogens.

The Dilution Effect Hypothesis (DEH) argues that greater biodiversity lowers the risk of disease and reduces the rates of pathogen transmission since more diverse communities harbour fewer competent hosts for any given pathogen, thereby reducing host exposure to the pathogen. DEH is expected to operate most intensely in vector-borne pathogens and when species-rich communities are not associated with increased host density. Overall, dilution will occur if greater species diversity leads to a lower contact rate between infected vectors and susceptible hosts, and between infected hosts and susceptible vectors. Field-based tests simultaneously analysing the prevalence of several multi-host pathogens in relation to host and vector diversity are required to validate DEH. We tested the relationship between the prevalence in house sparrows (Passer domesticus) of four vector-borne pathogens-three avian haemosporidians (including the avian malaria parasite Plasmodium and the malaria-like parasites Haemoproteus and Leucocytozoon) and West Nile virus (WNV)-and vertebrate diversity. Birds were sampled at 45 localities in SW Spain for which extensive data on vector (mosquitoes) and vertebrate communities exist. Vertebrate censuses were conducted to quantify avian and mammal density, species richness and evenness. Contrary to the predictions of DEH, WNV seroprevalence and haemosporidian prevalence were not negatively associated with either vertebrate species richness or evenness. Indeed, the opposite pattern was found, with positive relationships between avian species richness and WNV seroprevalence, and Leucocytozoon prevalence being detected. When vector (mosquito) richness and evenness were incorporated into the models, all the previous associations between WNV prevalence and the vertebrate community variables remained unchanged. No significant association was found for Plasmodium prevalence and vertebrate community variables in any of the models tested. Despite the studied system having several characteristics that should favour the dilution effect (i.e., vector-borne pathogens, an area where vector and host densities are unrelated, and where host richness is not associated with an increase in host density), none of the relationships between host species diversity and species richness, and pathogen prevalence supported DEH and, in fact, amplification was found for three of the four pathogens tested. Consequently, the range of pathogens and communities studied needs to be broadened if we are to understand the ecological factors that favour dilution and how often these conditions occur in nature.

Trypanosoma rangeli Genetic, Mammalian Hosts, and Geographical Diversity from Five Brazilian Biomes.

Trypanosoma rangeli is a generalist hemoflagellate that infects mammals and is transmitted by triatomines around Latin America. Due to its high genetic diversity, it can be classified into two to five lineages. In Brazil, its distribution outside the Amazon region is virtually unknown, and knowledge on the ecology of its lineages and on host species diversity requires further investigation. Here, we analyzed 57 T. rangeli samples obtained from hemocultures and blood clots of 1392 mammals captured in different Brazilian biomes. The samples were subjected to small subunit (SSU) rDNA amplification and sequencing to confirm T. rangeli infection. Phylogenetic inferences and haplotype networks were reconstructed to classify T. rangeli lineages and to infer the genetic diversity of the samples. The results obtained in our study highlighted both the mammalian host range and distribution of T. rangeli in Brazil: infection was observed in five new species (Procyon cancrivorous, Priodontes maximum, Alouatta belzebul, Sapajus libidinosus, and Trinomys dimidiatus), and transmission was observed in the Caatinga biome. The coati (Nasua nasua) and capuchin monkey (S. libidinosus) are the key hosts of T. rangeli. We identified all four T. rangeli lineages previously reported in Brazil (A, B, D, and E) and possibly two new genotypes.

Sarcoptic mange: An emerging panzootic in wildlife.

Sarcoptic mange, a skin infestation caused by the mite Sarcoptes scabiei, is an emerging disease for some species of wildlife, potentially jeopardizing their welfare and conservation. Sarcoptes scabiei has a near-global distribution facilitated by its forms of transmission and use of a large diversity of host species (many of those with broad geographic distribution). In this review, we synthesize the current knowledge concerning the geographic and host taxonomic distribution of mange in wildlife, the epidemiological connections between species, and the potential threat of sarcoptic mange for wildlife conservation. Recent sarcoptic mange outbreaks in wildlife appear to demonstrate ongoing geographic spread, increase in the number of hosts and increased virulence. Sarcoptic mange has been reported in at least 12 orders, 39 families and 148 species of domestic and wild mammals, making it one of the most generalist ectoparasites of mammals. Taxonomically, the orders with most species found infested so far include Perissodactyla(67% species from the entire order), Artiodactyla(47%), and Diprotodontia(67% from this order). This suggests that new species from these mammal orders are likely to suffer cross-species transmission and be reported positive to sarcoptic mange as surveillance improves. We propose a new agenda for the study of sarcoptic mange in wildlife, including the study of the global phylogeography of S.scabiei, linkages between ecological host traits and sarcoptic mange susceptibility, immunology of individuals and species, development of control strategies in wildlife outbreaks and the effects of global environmental change in the sarcoptic mange system. The ongoing transmission globally and sustained spread among areas and wildlife species make sarcoptic mange an emerging panzootic in wildlife. A better understanding of sarcoptic mange could illuminate the aspects of ecological and evolutionary drivers in cross-species transmission for many emerging diseases.

Emerging diversity and ongoing expansion of the genus Brucella.

Remarkable genetic diversity and breadth of host species has been uncovered in the Brucella genus over the past decade, fundamentally changing our concept of what it means to be a Brucella. From ocean fishes and marine mammals, to pond dwelling amphibians, forest foxes, desert rodents, and cave-dwelling bats, Brucella have revealed a variety of previously unknown niches. Classical microbiological techniques have been able to help us classify many of these new strains but at times have limited our ability to see the true relationships among or within species. The closest relatives of Brucella are soil bacteria and the adaptations of Brucella spp. to live intracellularly suggest that the genus has evolved to live in vertebrate hosts. Several recently discovered species appear to have phenotypes that are intermediate between soil bacteria and core Brucella, suggesting that they may represent ancestral traits that were subsequently lost in the traditional species. Remarkably, the broad relationships among Brucella species using a variety of sequence and fragment-based approaches have been upheld when using comparative genomics with whole genomes. Nonetheless, genomes are required for fine-scale resolution of many of the relationships and for understanding the evolutionary history of the genus. We expect that the coming decades will reveal many more hosts and previously unknown diversity in a wide range of environments.

Avian Influenza A Viruses Reassort and Diversify Differently in Mallards and Mammals.

Reassortment among co-infecting influenza A viruses (IAVs) is an important source of viral diversity and can facilitate expansion into novel host species. Indeed, reassortment played a key role in the evolution of the last three pandemic IAVs. Observed patterns of reassortment within a coinfected host are likely to be shaped by several factors, including viral load, the extent of viral mixing within the host and the stringency of selection. These factors in turn are expected to vary among the diverse host species that IAV infects. To investigate host differences in IAV reassortment, here we examined reassortment of two distinct avian IAVs within their natural host (mallards) and a mammalian model system (guinea pigs). Animals were co-inoculated with A/wildbird/California/187718-36/2008 (H3N8) and A/mallard/Colorado/P66F1-5/2008 (H4N6) viruses. Longitudinal samples were collected from the cloaca of mallards or the nasal tract of guinea pigs and viral genetic exchange was monitored by genotyping clonal isolates from these samples. Relative to those in guinea pigs, viral populations in mallards showed higher frequencies of reassortant genotypes and were characterized by higher genotype richness and diversity. In line with these observations, analysis of pairwise segment combinations revealed lower linkage disequilibrium in mallards as compared to guinea pigs. No clear longitudinal patterns in richness, diversity or linkage disequilibrium were present in either host. Our results reveal mallards to be a highly permissive host for IAV reassortment and suggest that reduced viral mixing limits avian IAV reassortment in a mammalian host.

Analysis of protein determinants of host-specific infection properties of polyomaviruses using machine learning.

The large tumor antigen (LT-Ag) and major capsid protein VP1 are known to play important roles in determining the host-specific infection properties of polyomaviruses (PyVs). The objective of this study was to investigate the physicochemical properties of amino acids of LT-Ag and VP1 that have important effects on host specificity, as well as classification techniques used to predict PyV hosts. We collected and used reference sequences of 86 viral species for analysis. Based on the clustering pattern of the reconstructed phylogenetic tree, the dataset was divided into three groups: mammalian, avian, and fish. We then used random forest (RF), naïve Bayes (NB), and k-nearest neighbors (kNN) algorithms for host classification. Among the three algorithms, classification accuracy using kNN was highest in both LT-Ag (ACC = 98.83) and VP1 (ACC = 96.51). The amino acid physicochemical property most strongly correlated with host classification was charge, followed by solvent accessibility, polarity, and hydrophobicity in LT-Ag. However, in VP1, amino acid composition showed the highest correlation with host classification, followed by charge, normalized van der Waals volume, and solvent accessibility. The results of the present study suggest the possibility of determining or predicting the host range and infection properties of PyVs at the molecular level by identifying the host species of active and emerging PyVs that exhibit different infection properties among diverse host species. Structural and biochemical differences of LT-Ag and VP1 proteins in host species that reflect these amino acid properties can be considered primary factors that determine the host specificity of PyV.

The proficiency of the original host species determines community-level plasmid dynamics.

Plasmids are common in natural bacterial communities, facilitating bacterial evolution via horizontal gene transfer. Bacterial species vary in their proficiency to host plasmids: whereas plasmids are stably maintained in some species regardless of selection for plasmid-encoded genes, in other species, even beneficial plasmids are rapidly lost. It is, however, unclear how this variation in host proficiency affects plasmid persistence in communities. Here, we test this using multispecies bacterial soil communities comprising species varying in their proficiency to host a large conjugative mercury resistance plasmid, pQBR103. The plasmid reached higher community-level abundance where beneficial and when introduced to the community in a more proficient host species. Proficient plasmid host species were also better able to disseminate the plasmid to a wider diversity of host species. These findings suggest that the dynamics of plasmids in natural bacterial communities depend not only upon the plasmid's attributes and the selective environment but also upon the proficiency of their host species.

Developmental asynchrony and host species identity predict variability in nestling growth of an obligate brood parasite: a test of the “growth-tuning” hypothesis

Generalist obligate brood parasites are excellent models for studies of developmental plasticity, as they experience a range of social and environmental variation when raised by one of their many hosts. Parasitic Brown-headed Cowbirds (Molothrus ater (Boddaert, 1783)) exhibit host-specific growth rates, yet Cowbird growth rates are not predicted by hosts’ incubation or brooding periods. We tested the novel “growth-tuning” hypothesis which predicts that total asynchrony between Cowbirds’ and hosts’ nesting periods results in faster parasitic growth in nests where host young fledge earlier than Cowbirds. We tested this prediction using previously published and newly added nestling mass data across diverse host species. Total nesting period asynchrony (summed across incubation and brooding stages) predicted Cowbird growth; 8-day-old Cowbirds were heavier in host nests with relatively shorter nesting periods. We further explored the drivers of variation in growth using mass measurements of Cowbirds in Song Sparrow (Melospiza melodia (A. Wilson, 1810)) and Red-winged Blackbird (Agelaius phoeniceus (Linnaeus, 1766)) nests. Our top models included host species (Cowbirds grew faster in Sparrow nests), numbers of nestmates (slowest when raised alone), and sex (males grew faster). These results confirm that multiple social and environmental factors predict directional patterns of developmental plasticity in avian generalist brood parasites.

Trade-Offs with Growth Limit Host Range in Complex Life-Cycle Helminths.

AbstractParasitic worms with complex life cycles have several developmental stages, with each stage creating opportunities to infect additional host species. Using a data set for 973 species of trophically transmitted acanthocephalans, cestodes, and nematodes, we confirmed that worms with longer life cycles (i.e., more successive hosts) infect a greater diversity of host species and taxa (after controlling for study effort). Generalism at the stage level was highest for middle life stages, the second and third intermediate hosts of long life cycles. By simulating life cycles in real food webs, we found that middle stages had more potential host species to infect, suggesting that opportunity constrains generalism. However, parasites usually infected fewer host species than expected from simulated cycles, suggesting that generalism has costs. There was no trade-off in generalism from one stage to the next, but worms spent less time growing and developing in stages where they infected more taxonomically diverse hosts. Our results demonstrate that life-cycle complexity favors high generalism and that host use across life stages is determined by both ecological opportunity and life-history trade-offs.