Host Traits Research Articles

The effects of salinity on the distribution and survival of two exotic ostracods in the Iberian Peninsula

Recent research highlighted the need to include experimental estimates of tolerance limits to varying environmental conditions when investigating what factors limit species distributions. However, most niche approaches are only based on the statistical dependence between environmental and occurrence data. Here, we combined field data with survival experiments to assess the role of salinity as a limiting factor in the distribution of two species of exotic ostracods from the Iberian Peninsula. Vizcainocypria viator is a free-living species associated with rice fields and Ankylocythere sinuosa is a commensal of the red swamp crayfish (Procambarus clarkii). Experiments and field data indicate that the distribution of V. viator is limited by adult survival at low and high salinities (below electrical conductivity of 0.6 mS/cm and above 10 mS/cm). In the case of A. sinuosa, the analysis of field data shows that its prevalence is negatively affected by high salinity, whereas experiments indicate an optimal survival at high salinities (conductivity above 10.2 mS/cm), thus suggesting that high salinity may impact A. sinuosa distribution indirectly through affecting host traits (e.g. reduced activity). The habitat of close ancestors (marine versus non-marine respectively for A. sinuosa and V. viator) most likely explains the contrasting differences in salinity tolerance between both ostracod species.

Beyond numbers: rethinking host professionalism on Airbnb

PurposeWe challenge the conventional approach to distinguish between professional and non-professional Airbnb hosts by solely using the number of managed listings.Design/methodology/approachWe leverage the recently released platform policy that categorizes hosts' professionalism by their self-declared status. Our multinomial modeling approach predicts true host status, factoring in the number of managed listings and controlling for listing and host traits. We employ data from five major European cities collected through scraping the Airbnb webpage.FindingsOur research reveals that relying solely on the number of listings managed falls short of accurately predicting the host type, leading to difficulties in evaluating the platform's impact on the local housing market and reducing the effectiveness of policy intervention. Moreover, we advocate using more fine-grained measures to differentiate further between semi-professional and professional hosts who exhibit heterogeneous economic behaviors.Research limitations/implicationsReliable professionalism metrics are essential to curb unethical practices, promote market transparency and ensure a level playing field for all market participants.Originality/valueThis work pioneers the revelation of the inadequacy of a commonly used measure for predicting host professionalism accurately.

The impacts of host traits on parasite infection of montane birds in southwestern China

Parasitic infections have the potential to impact the hosts’ body condition, elevate physiological responses, and ultimately lead to increased mortality. Host-parasite interactions are tied to the ecological and life-history traits of the hosts. While montane birds are susceptible to avian blood parasites, few studies have simultaneously assessed how inter- and intra-specific traits of hosts influence their probability of parasite infection. In this study, we screened for avian blood parasites across 214 individuals from 51 species at two sites, including a lowland farmland at 700 m and a highland forest at 2,500 m, in the Gaoligong Mountains in southwestern China. Overall blood parasite prevalence was 53.74%, with divergent species-specific prevalence ranging from 6.25% to 66.67%. We also measured traits indicative of body condition and physiological responses of each sampled individual. Using Bayesian phylogenetic logistic models, we assessed whether parasite infection probability is associated with ecological and life history traits of host species. Larger bird species were more likely to be infected than smaller bird species, and omnivore species showed lower susceptibility than those with other diets such as insectivores and herbivores. In contrast, foraging strata, nest type, and participation in mixed-species flocks of host species did not affect infection probability. We then used a reduced sample of eight species with more than five individuals, to assess the associations between intra-specific infection probability and host body condition, represented by fat and muscle reserves, and acute stress responses measured through breath rate. While infected individuals were likely to have more fat reserves than non-infected individuals, we did not find any association between infection probability and muscle reserve and body mass, nor with breath rate. Our results revealed that at the species level, specific traits (body mass and diet) of host species predict infection probability and implied a potential link at the individual level between enhanced body condition and increased resilience to parasite infection.

Host finding and probing behavior by Philaenus spumarius on olive varieties with a different degree of susceptibility to Xylella fastidiosa

Abundance on and access time to the host plant are the pivotal factors in Xylella fastidiosa transmission to olive by the meadow spittlebug Philaenus spumarius. Therefore, olive varieties suitable for the vectors, i.e., plants providing all the necessary cues to the insect for their location, settling and acceptance, and devoid of antixenotic defenses, could be more susceptible to infection than varieties non- or less suitable for the vector. Here we evaluated whether a bacterium-susceptible olive variety, Ogliarola Salentina, could be a more suitable host for P. spumarius than the two resistant varieties Leccino and FS-17. We carried out: (i) an evaluation of between-hosts and within-host preference; (ii) an insect survival analysis; (iii) an Electrical Penetration Graph (EPG)-assisted analysis of the probing behavior; (iv) light microscopy of the tissues the spittlebugs had access to; (v) an analysis of the xylem sap primary metabolites. In choice tests, the insect exhibited a significant preference for Ogliarola Salentina. In addition, spittlebugs displayed longer xylem sap ingestion bouts on the bacterium-susceptible variety compared to resistant genotypes, possibly because of differences in the xylem sap chemical profile rather than xylem anatomy. Spittlebugs preference for Ogliarola over both Leccino and FS-17 could be a relevant and so far overlooked component of the low disease prevalence in these two olive varieties reported in Southern Italian olive orchards. Overall, our data point toward the importance of incorporating studies on vector-plant interaction and host traits of resistance to the vector in research on genotypes resistant to X. fastidiosa.

Flexibility in coral–algal symbiosis is positively correlated with the host geographic range

AbstractGeneralists are thought to adapt to broader ecological conditions compared to less flexible specialists. However, few studies have systematically tested what ecological or life‐history traits are associated with organisms' ecological flexibility. Here, we used stony corals to test the relative effects of host traits and ecological factors on corals' flexibility to form photosymbioses with algae. We analysed data from 211 stony coral species to test if coral's geographic distribution, depth range, symbiont transmission mode or colony morphology predict coral–algal flexibility. We report a novel positive correlation between coral–algal flexibility and coral species' geographic range. Symbiont transmission mode was also a predictor of flexibility, albeit the result is less robust against sampling bias. Coral depth range and morphology did not show significant effects. We highlight that host–symbiont dispersal abilities, interactions and evolutionary histories likely contribute to the observed patterns. We urge conservation efforts to consider the ecological implications of coral–algal flexibility.

The evolutionary dynamics of hyperparasites

Evolutionary theory has typically focused on pairwise interactions, such as those between hosts and parasites, with relatively little work having been carried out on more complex interactions including hyperparasites: parasites of parasites. Hyperparasites are common in nature, with the chestnut blight fungus virus CHV-1 a well-known natural example, but also notably include the phages of important human bacterial diseases. We build a general modeling framework for the evolution of hyperparasites that highlights the central role that the ability of a hyperparasite to be transmitted with its parasite plays in their evolution. A key result is that hyperparasites which transmit with their parasite hosts (hitchhike) will be selected for lower virulence, trending towards hypermutualism or hypercommensalism. We examine the impact on the evolution of hyperparasite systems of a wide range of host and parasite traits showing, for example, that high parasite virulence selects for higher hyperparasite virulence resulting in reductions in parasite virulence when hyperparasitized. Furthermore, we show that acute parasite infection will also select for increased hyperparasite virulence. Our results have implications for hyperparasite research, both as biocontrol agents and for their role in shaping community ecology and evolution and moreover emphasize the importance of understanding evolution in the context of multitrophic interactions.

Parasite‐mediated changes in host traits alter food web dynamics

Parasites commonly alter the phenotype of their hosts, thereby influencing competitive and consumer–resource interactions. This could trigger a cascade effect on the dynamics of biological communities, but the role of parasites in ecosystem processes is poorly understood. In this study, we investigate how parasite‐induced trait modifications shape the dynamics of a complex lake food web using an allometric trophic network model (ATN). We simulated infections of stage‐structured fish host populations via increased maintenance costs and predation risk. Our results show that host trait modifications can significantly impact host demography, with stage‐specific biomass declines up to 60%. However, less severely affected host stages buffered these effects and sustained the population. Importantly, host biomass decline altered the dynamics of species interactions and these effects cascaded through the entire community, with biomass changes observed at all trophic levels. Our findings emphasize the importance of incorporating both indirect parasite effects and host life history in ecological network studies for more realistic simulations of community dynamics.

Spatial and temporal variability in infestation of Oregon oyster farms by shell-boring polychaetes

Shell-boring polychaetes burrow into the shells of cultivated and wild molluscs, leading to the formation of unsightly blisters that fill with mud, detritus, and fecal material. Infestation of cultivated oysters poses economic risks for the Pacific Northwest’s shellfish mariculture industry because the blisters reduce the aesthetic quality and market appeal of oysters sold on the half-shell market. To help Oregon’s multimillion-dollar mariculture industry develop resilience against this emerging biosecurity threat, we quantified seasonal variability and spatial differences in the infestation of Pacific oysters (Crassostrea gigas) by shell-boring polychaetes, and assessed whether prevalence varied among grow-out methods, seasons, and host traits (shell height and tissue mass). In 2019–2021, we obtained 829 Pacific oysters from seven commercial shellfish farms spanning the Oregon coast (Tillamook Bay, Netarts Bay, Yaquina Bay, and Coos Bay), and observed a mean statewide infestation rate of 11–31% over four sampling seasons. We observed the highest prevalence of infestation by shell-boring polychaetes (72%) in Netarts Bay. Oysters cultivated off-bottom exhibited lower prevalence of infestation than oysters grown on-bottom. Our study also revealed a significant effect of seasonality, with higher rates of infestation during winter. Oyster shell height and tissue mass were not significantly associated with the prevalence of infestation. Our observations identify an infestation hotspot in Netarts Bay, and suggest that off-bottom culture may help reduce infestation rates, mitigating damage caused by shell-boring polychaetes in Oregon bays and estuaries.

The structure and assembly mechanisms of T4-like cyanophages community in the South China Sea.

Marine ecosystems contain an immense diversity of phages, many of which infect cyanobacteria (cyanophage) that are largely responsible for primary productivity. To characterize the genetic diversity and biogeographic distribution of the marine T4-like cyanophage community in the northern South China Sea, the T4-like cyanophage portal protein gene (g20) was amplified. Phylogenetic analysis revealed that marine T4-like cyanophages were highly diverse, with g20 operational taxonomic units being affiliated with five defined clades (Clusters I-V). Cluster II had a wide geographic distribution, Cluster IV was the most abundant in the open sea, and Cluster I was dominant in coastal shelf environments. Our results showed T4-like cyanophages (based on g20) community was generally shaped via heterogeneous selection. Highly variable environmental factors (such as salinity and temperature) can heterogeneously select different cyanophage communities. Nevertheless, the dominant drivers of the T4-like cyanophage community based on the g20 and g23 (T4-like phage major capsid protein gene) were different, probably due to different coverages by the primer sets. Furthermore, the community assembly processes of T4-like cyanophages were affected by host traits (abundance and distribution), viral traits (latent period, burst size, and host range), and environmental properties (temperature and salinity).IMPORTANCECyanophages are abundant and ubiquitous in the oceans, altering population structures and evolution of cyanobacteria, which account for a large portion of global carbon fixation, through host mortality, horizontal gene transfer, and the modulation of host metabolism. However, little is known about the biogeography and ecological drivers that shape the cyanophage community. Here, we use g20 and g23 genes to examine the biogeographic patterns and the assembly mechanisms of T4-like cyanophage community in the northern part of the South China Sea. The different coverages of primer sets might lead to the different dominant drivers of T4-like cyanophage community based on g20 and g23 genes. Our results showed that characteristics of viral traits (latent period, burst size, and host range) and host traits (abundance and distribution) were found to either limit or enhance the biogeographic distribution of T4-like cyanophages. Overall, both virus and host properties are critical to consider when determining rules of community assembly for viruses.

Phylosymbiosis shapes skin bacterial communities and pathogen-protective function in Appalachian salamanders.

Phylosymbiosis is an association between host-associated microbiome composition and host phylogeny. This pattern can arise via the evolution of host traits, habitat preferences, diets, and the co-diversification of hosts and microbes. Understanding the drivers of phylosymbiosis is vital for modelling disease-microbiome interactions and manipulating microbiomes in multi-host systems. This study quantifies phylosymbiosis in Appalachian salamander skin in the context of infection by the fungal pathogen Batrachochytrium dendrobatidis (Bd), while accounting for environmental microbiome exposure. We sampled ten salamander species representing >150Myears of divergence, assessed their Bd infection status, and analysed their skin and environmental microbiomes. Our results reveal a significant signal of phylosymbiosis, whereas the local environmental pool of microbes, climate, geography, and Bd infection load had a smaller impact. Host-microbe co-speciation was not evident, indicating that the effect stems from the evolution of host traits influencing microbiome assembly. Bd infection is correlated with host phylogeny and the abundance of Bd-inhibitory bacterial strains, suggesting that the long-term evolutionary dynamics between salamander hosts and their skin microbiomes affect the present-day distribution of the pathogen, along with habitat-linked exposure risk. Five Bd-inhibitory bacterial strains showed unusual generalism: occurring in most host species and habitats. These generalist strains may enhance the likelihood of probiotic manipulations colonising and persisting on hosts. Our results underscore the substantial influence of host-microbiome eco-evolutionary dynamics on environmental health and disease outcomes.

The associational effects of host plant and mistletoe functional traits on leaf herbivory in mistletoe.

Associational effects are a phenomenon in which herbivore damage on co-occurring plant species is influenced by neighboring plants. Mistletoes are a group of shrubs that obtain nutrients from host plants through haustoria. Despite the potential for mistletoe herbivory to be affected by associational effects with their hosts, the effects of host and mistletoe functional traits on mistletoe herbivory have been largely overlooked. This study aimed to evaluate the associational effects of host plants and the direct effects of mistletoe functional traits on mistletoe herbivory. To achieve this, we measured leaf herbivory and leaf traits of three mistletoe species (Dendrophthoe pentandra, Scurrula chingii var. yunnanensis, and Helixanthera parasitica) and their associated 11 host species during both dry and wet seasons. Our results showed that leaf herbivory of D. pentandra and S. chingii var. yunnanensis differed significantly on their respective host species, but H. parasitica did not. The relationships between mistletoe and the paired host herbivory differed between seasons, with a stronger positive relationship observed during the dry season. Furthermore, significant relationships were observed between paired leaf carbon, leaf nitrogen, and condensed tannin in mistletoes and their host plants, indicating that host plants can affect mistletoes' leaf functional traits. A group of mistletoe leaf traits provided significant predictions for leaf herbivory: leaves with higher leaf thickness and leaf total nitrogen showed higher herbivory. Overall, our study reveals that mistletoe leaf herbivory is directly affected by its leaf traits and indirectly affected by host associational effects, primarily through changes in mistletoes' leaf traits.

Infection of Norway lobster (Nephrops norvegicus) by the parasite Hematodinium sp.: insights from 30 years of field observations.

The Norway lobster, Nephrops norvegicus, is an important representative of the benthos and also supports valuable fisheries across Europe. Nephrops are susceptible to infection by Hematodinium sp., an endoparasitic dinoflagellate that causes morbidity and mortality. From an epizootiological perspective, the Clyde Sea Area (CSA; west of Scotland) is the best-studied Hematodinium-Nephrops pathosystem, with historical data available between 1988 and 2008. We have revisited this pathosystem by curating and updating prevalence values, differentiating host traits associated with disease exposure and progression, and comparing Hematodinium sp. disease dynamics in the CSA to other locations and to other decapod hosts (Cancer pagurus, Carcinus maenas). Prevalence from a 2018/2019 survey (involving 1739 lobsters) revealed Hematodinium sp. still mounts a synchronized patent infection in the CSA; hence this pathogen can be considered as enzootic in this location. We highlight for the first time that Nephrops size is associated with high severity infection, while females are more exposed to Hematodinium sp. More generally, regardless of the host (Norway lobster, brown and shore crabs) or the geographical area (Ireland, Wales, Scotland), Hematodinium sp. patent infections peak in spring/summer and reach their nadir during autumn. We contend that Hematodinium must be considered one of the most important pathogens of decapod crustaceans in temperate waters.

Atributos das árvores hospedeiras, e não a diversidade da comunidade, conduzem a abundância de epífitas em florestas tropicais sazonais

Abstract Epiphytes are considered indicators of forest ecological integrity, but the factors that explain their abundance are still not well understood. We here evaluated tree colonization by epiphytes in old-growth monospecific reforestation stands of Astronium urundeuva (M.Allemão) Engl. (Anacardiaceae) and Eucalyptus saligna Sm. (Myrtaceae), in comparison to a neighbor seasonal tropical forest fragment under similar environmental conditions. In each forest type, we identified and measured all trees (planted and colonizers) from 5-cm stem diameter in five 200 m² plots and quantified all vascular epiphytes per tree. Tree species were categorized by bark roughness, canopy deciduousness and growth rate. The abundance of epiphytes and the frequency of host trees were higher in the A. urundeuva plantation than in the native forest, with the E. saligna stand in an intermediate position. Also, we found that host traits influenced the abundance of epiphytes in their trunks. Host trees had average stem perimeter and height both higher than non-hosts, which indicates that colonization is more likely to occur in older trees. The average abundance of epiphytes per tree was higher in species with rough bark, but no relationship was found with canopy deciduousness or tree growth rate. We evidenced, therefore, that forest plantations, even if monospecific, can provide habitat for epiphytes. However, at community level, colonization success, either in native or restored forest, depends on the relative abundance of species whose bark type favors epiphytes establishment.

A meta‐analysis exploring associations between habitat degradation and Neotropical bat virus prevalence and seroprevalence

Habitat degradation can increase zoonotic disease risks by altering infection dynamics in wildlife and increasing wildlife–human interactions. Bats are an important taxonomic group to consider these effects, because they harbour many relevant zoonotic viruses and have species‐ and context‐dependent responses to degradation that could affect zoonotic virus dynamics. Yet our understanding of the associations between habitat degradation and bat virus prevalence and seroprevalence are limited to a small number of studies, which often differ in the bats or viruses sampled, the study region, and methodology. To develop a broad understanding of the associations between bat viruses and habitat degradation, we conducted an initial phylogenetic meta‐analysis that combines published prevalence and seroprevalence (‘(sero)prevalence') with remote‐sensing habitat degradation data. Our dataset includes 588 unique records of (sero)prevalence across 16 studies, 64 bat species, and five virus families. We quantified the overall strength and direction of the relationship between habitat degradation and bat virus outcomes and tested how this relationship is moderated by the time between habitat degradation and bat sampling and by ecological traits of bat hosts while controlling for phylogenetic non‐independence among bat species. We found no effect of degradation on prevalence overall, although a weak effect may exist when forest loss occurs the year prior to bat sampling. In contrast, we detected a negative but weak association between degradation and seroprevalence overall that was strengthened when forest loss occurred the year prior to bat sampling. No bat traits that we investigated interacted with habitat degradation to impact virus outcomes, suggesting observed trends are independent of these traits. Biases in our initial dataset highlight opportunities for future work; prevalence was highly zero‐inflated, and seroprevalence was dominated by Desmodus rotundus and rabies virus. These findings and subsequent analyses will improve our understanding of how global change affects host–pathogen dynamics.

Variability of biological traits of Bulinus truncatus and Biomphalaria pfeifferi, the intermediate host snails of schistosomiasis, from three climatic zones of Côte d’Ivoire

Background: Schistosomiasis is endemic throughout all regions of Côte d’Ivoire, however, species of the intermediate snail host vary across bioclimatic zones. Hence, a deeper knowledge of the influence of climatic on the life history traits of the intermediate snail host is crucial to understand the environmental determinants of schistosomiasis in a rapidly changing climate. The aim of this study was to run a common garden experiment to assess differences in survival, somatic growth and fecundity of both Bulinus truncatus and Biomphalaria pfeifferi snails collected in three different bioclimatic areas.Methods: A cross-sectional malacological survey was conducted in February 2021 in the south, center and north of Côte d’Ivoire. We sampled two populations of B. truncatus, the intermediate host snail of Schistosoma haematobium, from northern and central Côte d’Ivoire, and two populations of Bi. pfeifferi, the intermediate host snail for Schistosoma mansoni, from the southern and central regions. Snails collected at the human-water contact sites were brought in the laboratory where they reproduced. The first generation snails (G1) for each population were reared under the same laboratory conditions, i.e., at 24°C–26°C, during 63 days (9 weeks), to estimate survival, growth, and fecundity.Results: We found that G1Bulinus snails from the north population showed higher survival and growth rates during our study and higher number of eggs at first reproduction, compared to the ones from the central region. For Bi. pfeifferi, no significant difference in survival rate was observed between G1 snails from the southern and central populations, whereas those from the south exhibited higher growth rates and higher number of eggs per individual at first reproduction than G1 snails from the central population.Conclusion: Our study provides evidence for heterogeneity in snails’ life-history traits in response to temperature among the populations from the three climatic regions. Further experiments from multiple populations are needed to confirm that snails express traits under optimal conditions, can lead to expansion of their geographical range and hence an increase in the risk of schistosomiasis transmission. Transplantation experiments will be required to assess implications of the changing climate on snails persistence, distribution and abundance.

Modeling the Impact of Proportion, Sowing Date, and Architectural Traits of a Companion Crop on Foliar Fungal Pathogens of Wheat in Crop Mixtures.

Diversification of cropping systems is a lever for the management of epidemics. However, most research to date has focused on cultivar mixtures, especially for cereals, even though crop mixtures can also improve disease management. To investigate the benefits of crop mixtures, we studied the effect of different crop mixture characteristics (i.e., companion proportion, sowing date, and traits) on the protective effect of the mixture. We developed a SEIR (Susceptible, Exposed, Infectious, Removed) model of two damaging wheat diseases (Zymoseptoria tritici and Puccinia triticina), which were applied to different canopy components, ascribable to wheat and a theoretical companion crop. We used the model to study the sensitivity of disease intensity to the following parameters: wheat-versus-companion proportion, companion sowing date and growth, and architectural traits. For both pathogens, the companion proportion had the strongest effect, with 25% of companion reducing disease severity by 50%. However, changing companion growth and architectural traits also significantly improved the protective effect. The effect of companion characteristics was consistent across different weather conditions. After decomposing the dilution and barrier effects, the model suggested that the barrier effect is maximized for an intermediate proportion of companion crop. Our study thus supports crop mixtures as a promising strategy to improve disease management. Future studies should identify real species and determine the combination of host and companion traits to maximize the protective effect of the mixture. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Specific gastrointestinal microbiota profiles in Chinese Tan sheep are associated with lauric acid content in muscle

The biological mechanisms underlying meat quality remain unclear. Currently, many studies report that the gastrointestinal microbiota is essential for animal growth and performance. However, it is uncertain which bacterial species are specifically associated with the meat quality traits. In this study, 16S rDNA and metagenomic sequencing were performed to explore the composition and function of microbes in various gastrointestinal segments of Tan sheep and Dorper sheep, as well as the relationship between microbiota and meat quality (specifically, the fatty acid content of the muscle). In the ruminal, duodenal, and colonic microbiome, several bacteria were uniquely identified in respective breeds, including Agrobacterium tumefaciens, Bacteroidales bacterium CF, and several members of the family Oscillospiraceae. The annotation of GO, KEGG, and CAZYme revealed that these different bacterial species were linked to the metabolism of glucose, lipids, and amino acids. Additionally, our findings suggested that 16 microbial species may be essential to the content of fatty acids in the muscle, especially C12:0 (lauric acid). 4 bacterial species, including Achromobacter xylosoxidans, Mageeibacillus indolicus, and Mycobacterium dioxanotrophicus, were positively correlated with C12:0, while 13 bacteria, including Methanobrevibacter millerae, Bacteroidales bacterium CF, and Bacteroides coprosuis were negatively correlated with C12:0. In a word, this study provides a basic data for better understanding the interaction between ruminant gastrointestinal microorganisms and the meat quality traits of hosts.

Phylosymbiosis: The Eco-Evolutionary Pattern of Insect-Symbiont Interactions.

Insects harbor diverse assemblages of bacterial and fungal symbionts, which play crucial roles in host life history. Insects and their various symbionts represent a good model for studying host-microbe interactions. Phylosymbiosis is used to describe an eco-evolutionary pattern, providing a new cross-system trend in the research of host-associated microbiota. The phylosymbiosis pattern is characterized by a significant positive correlation between the host phylogeny and microbial community dissimilarities. Although host-symbiont interactions have been demonstrated in many insect groups, our knowledge of the prevalence and mechanisms of phylosymbiosis in insects is still limited. Here, we provide an order-by-order summary of the phylosymbiosis patterns in insects, including Blattodea, Coleoptera, Diptera, Hemiptera, Hymenoptera, and Lepidoptera. Then, we highlight the potential contributions of stochastic effects, evolutionary processes, and ecological filtering in shaping phylosymbiotic microbiota. Phylosymbiosis in insects can arise from a combination of stochastic and deterministic mechanisms, such as the dispersal limitations of microbes, codiversification between symbionts and hosts, and the filtering of phylogenetically conserved host traits (incl., host immune system, diet, and physiological characteristics).

Aggregation of symbionts on hosts depends on interaction type and host traits

Symbionts tend to be aggregated on their hosts, such that few hosts harbor the majority of symbionts. This ubiquitous pattern can result from stochastic processes, but aggregation patterns may also depend on the type of host–symbiont interaction, along with traits that affect host exposure and susceptibility to symbionts. Untangling how aggregation patterns both within and among populations depend on stochastic processes, interaction type and host traits remains an outstanding challenge. Here, we address this challenge by using null models to compare aggregation patterns in a neutral system of Balanomorpha barnacles attached to patellid limpets and a host–parasite system of Gyrodactylus spp. monogeneans and their Trinidadian guppy Poecilia reticulata hosts. We first used a model to predict patterns of symbiont–host aggregation due to random partitioning of symbionts to hosts. This null model accurately predicted the aggregation of barnacles on limpets, but the degree of aggregation varied across 303 quadrats. Quadrats with larger limpets had less aggregated barnacles, whereas aggregation increased with variation in limpet size. Across 84 guppy populations, Gyrodactylus spp. parasites were significantly less aggregated than predicted by the null model. As in the neutral limpet–barnacle system, aggregation decreased with mean host size. Parasites were significantly less aggregated on males than females because male guppies tended to have higher prevalence and lower parasite burdens than predicted by the null model. Together, these results suggest stochastic processes can explain aggregation patterns in neutral but not parasitic systems, though in both systems host traits affect aggregation patterns. Because the distribution of symbionts on hosts can affect symbiont evolution via intraspecific interactions, and host behavior and evolution via host–symbiont interactions, identifying the drivers of aggregation enriches our understanding of host–symbiont interactions.

The functional traits of host fish can act as good predictors for parasite composition in a neotropical floodplain.

Parasite diversity can be influenced by the interaction of environmental factors and host traits, but understanding which traits can be decisive for the establishment of the parasite may provide subsidies fora better understanding of the host-parasite relationship. In this study, we investigated whether functional traits, diet, and host phylogeny can predict the similarity of the endoparasite composition of a fish assemblage in a Brazilian floodplain. Of the three evaluated components, the host's diet was the factor that showed the greatest influence on the composition and similarity of endoparasites, demonstrating the highest value of the explanation. The functional traits and phylogeny, despite presenting significant values (unique effect and global effect), showed low explainability in the composition of the endoparasites. When analyzing the joint effects, all components showed significant influence. Hosts that live in the same environment that are phylogenetically related and have a similar ecology have a certain degree of homogeneity in their parasite assemblages and, because they are endoparasites (which are acquired trophically along the chain), diet is the main driver of parasite richness and similarity. Overall, host traits can be one of the main determinants of parasite composition, so studies that address the functional traits of the host provide a representation of local diversity and define the possible patterns of these parasite communities.