Functional traits shape small mammal-helminth network: patterns and processes in species interactions

Exploring interactions between parasites and their hosts in the Pantanal floodplain using an ecological network approach

The study of host-parasite interactions is essential to understand the role of each host species in the parasitic transmission cycles in a given community. The use of ecological network highlights the patterns of interactions between hosts and parasites, allowing us to evaluate the underlying structural features and epidemiological roles of different species within this context. Through network analysis, we aimed to understand the epidemiological roles of mammalian hosts species (n = 67) and their parasites (n = 257) in the Pantanal biome. Our analysis revealed a modular pattern within the network, characterized by 14 distinct modules, as well as nestedness patterns within these modules. Some key nodes, such as the multi-host parasites Trypanosoma cruzi and T. evansi, connect different modules and species. These central nodes showed us that various hosts species, including those with high local abundances, contribute to parasite maintenance. Ectoparasites, such as ticks and fleas, exhibit connections that reflect their roles as vectors of certain parasites. Overall, our findings contribute to a comprehensive understanding of the structure of host-parasite interactions in the Pantanal ecosystem, highlighting the importance of network analysis as a tool to identifying the main transmission routes and maintenance of parasites pathways. Such insights are valuable for parasitic disease control and prevention strategies and shed light on the broader complexities of ecological communities.

Nestedness and beta diversity of gastrointestinal helminth communities in common warthogs, Phacochoerus africanus (Suidae), at 2 localities in South Africa

Few studies have investigated the ecological interactions between wild species of Suidae and their parasites, leaving our knowledge concerning this host–parasite system fragmented. In the present study, we applied network studies to analyse community nestedness in helminth assemblages of common warthogs, Phacochoerus africanus (Gmelin) (Suidae). Helminth data were compiled from 95 warthogs, including young and adult males and females, from 2 different conservation areas in Mpumalanga and Limpopo Provinces, South Africa, collected monthly over a period of 1 year each. The aim was to study the effect of host sex, age and season of sampling on the structure of helminth infracommunities harboured by the warthogs and to search for non-random structural patterns in the warthog–helminth interaction networks. Furthermore, we investigated the influence of a warthog's age, sex and season of sampling on beta diversity and dark diversity of their helminth infracommunities. Lastly, we asked whether the effects of host sex, age and sampling season on helminth communities differed between the 2 localities. We found that helminth communities of warthogs were nested and host–parasite interactions were influenced by all 3 factors as well as combinations thereof. However, the resulting patterns differed at the 2 localities, indicating that local environmental processes are important drivers of community structure.

Sensitivity of bipartite network analyses to incomplete sampling and taxonomic uncertainty

Bipartite network analysis is a powerful tool to study the processes structuring interactions in ecological communities. In applying the method, it is assumed that the sampled interactions provide an accurate representation of the actual community. However, acquiring a representative sample may be difficult as not all species are equally abundant or easily identifiable. Two potential sampling issues can compromise the conclusions of bipartite network analyses: failure to capture the full range of interactions (sampling completeness) and use of a taxonomic level higher than species to evaluate the network (taxonomic resolution). We asked how commonly used descriptors of bipartite antagonistic communities (modularity, nestedness, connectance, and specialization [H₂ ']) are affected by reduced host sampling completeness, parasite taxonomic resolution, and their crossed effect, as they are likely to co-occur. We used a quantitative niche model to generate weighted bipartite networks that resembled natural host-parasite communities. The descriptors were more sensitive to uncertainty in parasite taxonomic resolution than to host sampling completeness. When only 10% of parasite taxonomic resolution was retained, modularity and specialization decreased by ~76% and ~12%, respectively, and nestedness and connectance increased by ~114% and ~345% respectively. The loss of taxonomic resolution led to a wide range of possible communities, which made it difficult to predict its effects on a given network. With regards to host sampling completeness, standardized nestedness, connectance, and specialization were robust, whereas modularity was sensitive (~30% decrease). The combination of both sampling issues had an additive effect on modularity. In communities with low effort for both sampling issues (50%-10% of sampling completeness and taxonomic resolution), estimators of modularity, and nestedness could not be distinguished from those of random assemblages. Thus, the categorical description of communities with low sampling effort (e.g., if a community is modular or not) should be done with caution. We recommend evaluating both sampling completeness and taxonomic certainty when conducting bipartite network analyses. Care should also be exercised when using nonrobust descriptors (the four descriptors for parasite taxonomic resolution; modularity for host sampling completeness) when sampling issues are likely to affect a dataset.

Impact of host sex and age on the diversity of endoparasites and structure of individual-based host-parasite networks in nyalas (Tragelaphus angasii Angas) from three game reserves in KwaZulu-Natal province, South Africa

In recent years, numerous studies have examined the effect of host sex and age on the structure of parasite communities in several host taxa under various environmental conditions and in different geographic regions. However, the influence of such factors on the structure of host-parasite networks has received less attention, and remarkably few studies have been carried out on large terrestrial mammals. In this study, we investigated the effects of host age and sex on the parasite infra- and component communities of nyalas (Tragelaphus angasii) and on the structure of individual-based nyala-endoparasite networks. We also aimed to evaluate to what extent these effects vary spatially and if they are mediated by conservation management. Based on a data set of internal macroparasites of 74 nyalas from three game reserves in KwaZulu-Natal province, we found that host age strongly influenced parasite community structure as well as the structure of parasite-nyala networks, whereas host sex played a minor role. However, the effects of both host sex and age were mediated by environmental conditions and thus led to different patterns at the three localities. Our findings highlight that host-parasite communities from different localities should not be pooled when conducting host-parasite network and community studies as this may bias results and mask patterns that are typical for a given locality.

Socioecological vulnerability and the risk of zoonotic disease emergence in Brazil

In developing countries, outbreaks of zoonotic diseases (ZDs) result from intertwined ecological, socioeconomic, and demographic processes that shape conditions for (i) increased contact between vulnerable human population and wildlife in areas undergoing environmental degradation and (ii) the rapid geographic spread of infections across socially vulnerable regions. In Brazil, recent increases in environmental and social vulnerabilities, amplified by economic and political crises, are potential triggers for outbreaks. We discuss Brazilian features that favor outbreaks and show a novel quantitative method for zoonotic risk assessment. Using data on nine ZDs from 2001 to 2019, we found that the most significant causal variables were vegetation cover and city remoteness. Furthermore, 8 of 27 states presented low-level risk of ZD outbreaks. Given the ZD-bushmeat connection, we identified central hunted mammals that should be surveilled to prevent spillover events. The current challenge is to coordinate intersectoral collaboration for effective One Health management in megadiverse countries with high social vulnerability and growing environmental degradation like Brazil.

Population genetic structure and phenotypic diversity of Aspidodera raillieti (Nematoda: Heterakoidea), a parasite of Didelphini marsupials in Brazil's South and Southeast Atlantic Forest

Background

The population genetics of parasites may be influenced by host specificity, life cycle, host geographical range, evolutionary history, and host population structure. The nematode Aspidodera raillieti infects different marsupial and rodent hosts in the Nearctic and Neotropical regions, implying a gene flow among populations. However, niche diversification of the main hosts of A. raillieti in superimposed areas may provide conditions for population genetic structuring within this parasite species. We examined the genetic structuring of A. raillieti infecting three marsupial species co-occurring along the South and Southeast Brazilian Atlantic Forest, a hotspot of biodiversity.

Methods

We employed morphometric analyses and partial mitochondrial cytochrome c oxidase I gene sequences (MT-CO1) to characterize populations via phylogenetic and phylogeographic analyses.

Results

Among 175 A. raillieti specimens recovered from the marsupial hosts Didelphis aurita, D. albiventris, and Philander quica, we identified 99 MT-CO1 haplotypes forming four haplogroups and four clades in networks and phylogenetic trees, respectively. Clades I and II encompassed parasites of D. albiventris from the South region, clade III comprised parasites of D. aurita from the South and Southeast regions, and clade IV encompassed parasites of D. aurita and D. albiventris from the South and Southeast regions and parasites of P. quica from the South region. High genetic differentiation between clades, with a high fixation index and greater genetic variation in the analysis of molecular variance (AMOVA), indicated low gene flow between clades. Haplotypes shared among host species revealed a lack of host specificity. A significant correlation in the Mantel test suggested parasite isolation by distance, while there was no evidence of geographical structure between populations. Negative neutrality test values for clades III and IV suggested recent population expansion. Morphometric differentiation between A. raillieti specimens recovered from different host species, as well as from different localities, was more evident in males.

Conclusion

The genetic structure of A. raillieti populations in the South and Southeast Atlantic Forest resulted from historical events rather than from current geographical distribution or host specificity. We also demonstrate morphometric variation associated with host species and localities, suggesting phenotypic plasticity to host attributes and to spatial variables.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05288-6.

Composition and structure of the helminth community of rodents in matrix habitat areas of the Atlantic forest of southeastern Brazil

The predominant landscape of the Atlantic Forest of the Brazilian state of Rio de Janeiro is made up of forest fragments surrounded by a matrix of modified habitat, which may influence the occurrence and distribution of host species and their parasites in comparison with the original continuous forest. The present study describes the structure, composition, and diversity of the helminth community found in rodents in two areas of an open matrix of different status of conservation. The abundance, intensity, and prevalence were calculated for each helminth species in rodent species. The influence of biotic and abiotic factors on the abundance and prevalence of the helminth species was also investigated. Community structure was analyzed based on the beta diversity and a bipartite network. Nine helminth species were recovered from Akodon cursor, Necromys lasiurus and Mus musculus, with the greatest helminth species richness being recorded in A. cursor (S = 8), followed by N. lasiurus (S = 6), and M. musculus (S = 3). Only three of the helminths recorded in A. cursor had been recorded previously in this rodent in the Atlantic Forest, where 12 different helminths have been recorded, so that the other five are new occurrences for this rodent. All the helminth species of N. lasiurus had been reported previously in this rodent in the Cerrado and Caatinga regions. Mus musculus was infected with the same helminths as the local fauna. Host species and locality were the most important factors influencing helminth abundance and prevalence. Beta-diversity was high for infracommunities indicating more substitutions of helminth species than losses among individuals. Three helminths species were shared by the three host species. The reduced beta-diversity observed in the component communities was consistent with the overlap observed in the helminth fauna of the host species.