Microbiome Heritability and Its Role in Adaptation of Hosts to Novel Resources

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

Microbiome and environment explain the absence of correlations between consumers and their diet in Bornean microsnails

Classical ecological theory posits that species partition resources such that each species occupies a unique resource niche. In general, the availability of more resources allows more species to co‐occur. Thus, a strong relationship between communities of consumers and their resources is expected. However, correlations may be influenced by other layers in the food web, or by the environment. Here we show, by studying the relationship between communities of consumers (land snails) and individual diets (from seed plants), that there is in fact no direct, or at most a weak but negative, relationship. However, we found that the diversity of the individual microbiome positively correlates with both consumer community diversity and individual diet diversity in three target species. Moreover, these correlations were affected by various environmental variables, such as anthropogenic activity, habitat island size, and a possibly important nutrient source, guano runoff from nearby caves. Our results suggest that the microbiome and the environment explain the absence of correlations between diet and consumer community diversity. Hence, we advocate that microbiome inventories are routinely added to any community dietary analysis, which our study shows can be done with relatively little extra effort. Our approach presents the tools to quickly obtain an overview of the relationships between consumers and their resources. We anticipate our approach to be useful for ecologists and environmentalist studying different communities in a local food web

Plant diets of land snail community members are similar in composition but differ in richness

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 15.3x). 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 communit