No abstract

Animals may host diverse bacterial communities that can markedly affect their behavioral physiology, ecology, and vulnerability to disease. Fungus-farming ants represent a classical example of mutualism that depends on symbiotic microorganisms. Unraveling the bacterial communities associated with fungus-farming ants is essential to understand the role of these microorganisms in the ant-fungus symbiosis. The bacterial community structure of five species of fungus-farmers (non-leaf-cutters; genera Mycocepurus, Mycetarotes, Mycetophylax, and Sericomyrmex) from three different environments in the Brazilian Atlantic rainforest (lowland forest, restinga forest, and sand dunes) was characterized with amplicon-based Illumina sequencing of 16 S ribosomal RNA gene. Possible differences in bacterial communities between ants internal to the nest (on the fungus garden) and external foragers were also investigated. Our results on the richness and diversity of associated bacteria provide novel evidence that these communities are host- and colony-specific in fungus-farming ants. Indeed, the bacterial communities associated with external foragers differ among the five species, and among colonies of the same species. Furthermore, bacterial communities from internal ants vs. foragers do not differ or differ only slightly within each ant species. This study highlights the importance of describing ant-associated bacterial communities to better understand this host-bacterial interaction in the social environment of insect colonies and provides the foundation for future studies on the ecological and evolutionary processes that drive the success of fungus-farming ants.

Leaf litter fuels secondary production in many aquatic ecosystems. Although the identity and species richness of leaf litter have been shown to influence ecosystem functioning and food‐web composition, it has been challenging to relate such patterns to mechanisms based on litter traits. Here, we investigate how six different leaf litter species, and their mixture, affect litter decomposition, as well as the colonisation and survival of associated aquatic invertebrates in natural microecosystems (tank bromeliads). We then ask whether these effects of litter composition are explained by chemical and structural traits of the litter. Litter composition affected decomposition rates, assembly of aquatic macroinvertebrates in bromeliads and survival of some detritivores (e.g. Chironomidae). In general, most of this effect of litter composition was due to differences between litter species, not between single‐species and six‐species mixtures, and could be explained in terms of two dominant axes in litter traits. Decomposition was fastest in litters with high specific leaf area (SLA), N:P ratios and N and P contents, and slowest in litters with high lignin content and C:N ratios. Chironomid survival was also greatest on high N, N:P and SLA litters. Our results highlight the importance of considering leaf litter traits on the structure and functioning of freshwater ecosystems in future studies. More broadly, these results add to a growing consensus that functional traits of resource species, rather than the number of resource species, are essential to predicting resource–consumer interactions in food webs.

The host-associated microbiome is vital to host immunity and pathogen defense. In aquatic ecosystems, organisms may interact with environmental bacteria to influence the pool of potential symbionts, but the effects of these interactions on host microbiome assembly and pathogen resistance are unresolved. We used replicated bromeliad microecosystems to test for indirect effects of arthropod–bacteria interactions on host microbiome assembly and pathogen burden, using tadpoles and the fungal amphibian pathogen Batrachochytrium dendrobatidis as a model host–pathogen system. Arthropods influenced host microbiome assembly by altering the pool of environmental bacteria, with arthropod–bacteria interactions specifically reducing host colonization by transient bacteria and promoting antimicrobial components of aquatic bacterial communities. Arthropods also reduced fungal zoospores in the environment, but fungal infection burdens in tadpoles corresponded most closely with arthropod-mediated patterns in microbiome assembly. This result indicates that the cascading effects of arthropods on the maintenance of a protective host microbiome may be more strongly linked to host health than negative effects of arthropods on pools of pathogenic zoospores. Our work reveals tight links between healthy ecosystem dynamics and the functioning of host microbiomes, suggesting that ecosystem disturbances such as loss of arthropods may have downstream effects on host-associated microbial pathogen defenses and host fitness.

Environment, litter composition and decomposer community are known to be the main drivers of litter decomposition in aquatic ecosystems. However, it remains unclear whether litter quality or functional diversity prevails under warming conditions. Using tank bromeliad ecosystems, we evaluated the combined effects of warming, litter quality and litter functional diversity on the decomposition process. We also assessed the contribution of macroinvertebrates and microorganisms in explaining litter decomposition patterns using litter bags made with different mesh sizes. Our results showed that litter decomposition was driven by litter functional diversity and was increasingly higher under warming, in both mesh sizes. Decomposition was explained by increasing litter dissimilarities in C and N. Our results highlight the importance of considering different aspects of litter characteristics (e.g., quality and functional diversity) in order to predict the decomposition process in freshwater ecosystems. Considering the joint effect of warming and litter traits aspects allow a more refined understanding of the underlying mechanisms of climate change and biodiversity shifts effects on ecosystem functioning.