Microbiomes are involved in most vital processes, such as immune response, detoxification, and digestion and are thereby elementary to organismal functioning and ultimately the host’s fitness. In turn, the microbiome may be influenced by the host and by the host’s environment. To understand microbiome dynamics during the process of adaptation to new resources, we performed an evolutionary experiment with the two-spotted spider mite, Tetranychus urticae. We generated genetically depleted strains of the two-spotted spider mite and reared them on their ancestral host plant and two novel host plants for approximately 12 generations. The use of genetically depleted strains reduced the magnitude of genetic adaptation of the spider mite host to the new resource and, hence, allowed for better detection of signals of adaptation via the microbiome. During the course of adaptation, we tested spider mite performance (number of eggs laid and longevity) and characterized the bacterial component of its microbiome (16S rRNA gene sequencing) to determine: (1) whether the bacterial communities were shaped by mite ancestry or plant environment and (2) whether the spider mites’ performance and microbiome composition were related. We found that spider mite performance on the novel host plants was clearly correlated with microbiome composition. Because our results show that only little of the total variation in the microbiome can be explained by the properties of the host (spider mite) and the environment (plant species) we studied, we argue that the bacterial community within hosts could be valuable for understanding a species’ performance on multiple resources.

Herbivore diets are often generalistic, and communities of herbivores tend to share much of their diets. In the tropical lowlands of Malaysian Borneo, tens of different noncarnivorous land snail species are able to coexist in communities on limestone outcrops. We tried to answer the question whether diet differentiation plays a role in their coexistence. We show, with a large metabarcoding study of the plant diet from gut contents of 658 individual snails (from 26 species, with a focus on three of the most common species in the region), that the different snail species indeed share much of their plant diet, but that mean diet richness varies strongly among species (up to 15.3×). These differences are mostly explained by snail size, with larger snails having wider diets. Furthermore, phylogenetic analyses of the plant diet by individual snails showed signs of clustering in c. 28% of the individuals, possibly suggesting phylogenetic specialization, although such clustering was weak when diets were considered by species. We discuss how observed trends in diet richness and diet clustering could also be explained by random feeding, with larger species simply eating more or less specifically, and by other, noncompetitive interactions, such as snails avoiding desiccation. Our study shows how to efficiently put the power of metabarcoding to work in unravelling the complex community processes commonly encountered in tropical ecosystems and is thus of substantial relevance to both community ecologists and conservationists.

Triazole resistance in the airborne human fungal pathogen Aspergillus fumigatus is a significant human health problem as the environmental use of triazoles has selected for cross-resistance to life-saving clinical triazoles in medicine. Despite the environment being well established as a source of triazole resistant A. fumigatus spores, the aerial transmission from the environment to patients remains unclear. This is mainly due to the lack of an affordable, reliable, and simple-to-use method for wide-scale environmental air sampling. Previous methods were ineffective in capturing sufficient A. fumigatus colony-forming units (CFUs) to allow the quantitative assessment of aerial triazole resistance fractions. Here we show that 14 days of exposure of sticky seals to the air along with selectively culturing colonies directly from the seals proved key for increasing CFUs per sample. We also tested the use of delta traps for passive outdoor spore capture and show that together with the sticky seals and selective culturing, they are a simple and effective tool for outdoor air sampling. We suggest the use of this cost-effective air sampling technique for wide-scale outdoor sampling to map resistance fractions, assess health risks, and pinpoint environmental resistance hot- and coldspots. Doing so will close the knowledge gap between environmental triazole resistance selection and the transmission to patients.

No abstract