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Insects harbor a large diversity of uncharted mutualistic and antagonistic microbes, with a potentially major impact on ecosystem services and crop, animal and human health. Still, the macrobiota associated microbiomes are often ignored in biodiversity surveys. While the Swedish insect macrobiome ranks among the best documented faunas in the world, we have only seen the first glimpses of the microbiome associated with these organisms; for Madagascar, where we have only discovered the tip of the iceberg of the macrobiome, the microbiome is largely terra incognita. Here, we take advantage of the massive sampling of the macrobiome across the two countries to characterize the associated microbiome and provide new insights into the processes shaping it. This part of the project is done in close collaboration with the Symbiosis Evolution Group, at Jagiellonian University in Kraków. The key questions we will address are:

1. Spatial patterns of microbial diversity

We will utilize the sampling of 200 sites in Sweden and 50 sites in Madagascar to explore how microbial richness, diversity and community composition vary within and between the countries. We will identify biogeographic areas and hotspots of biodiversity for the microbial community, and test whether these patterns overlap with biogeographic regions and hotspots known for the macrobiota.

2. Seasonal patterns of microbial diversity

The microbial diversity and species

composition may vary across the season, which is of particular relevance for the harmful microbes.

3. The drivers of microbial diversity

We can make full use of the ecological and land-use data collected for the sampling sites to identify the spatial and seasonal drivers affecting the microbial communities. This will clarify whether the microbiome depends on site-level characteristics like climate and soil type, the characteristics of present and past land use, or the composition or diversity of the host species community.

4. The individual microbiome

We will link individual microbes to individual host species or clades by sequencing selected individual specimens covering a broad phylogenetic and geographic range. This will allow us to identify the factors that drive the diversity of the insect microbiome as well as assessing to what degree community composition of host-associated microbiomes parallels the phylogeny of host species (i.e. phylosymbiosis).

5. Microbes as indicator species

While macroscopic organisms are more commonly used as indicator species, this may be a historical legacy. Since the insect-associated microbial community likely reflects both the host species community, environmental conditions and feeding patterns of the insect community, it may contain more ecosystem information than the insect community itself.

6. Harmful microbes

Insects act as vectors for a range of microbial pathogens causing

diseases in human, animals and crops. We will investigate how composition of the vector community together with habitat and landscape factors influence the prevalence of specific pathogens, as well as monitor how the prevalence changes over the season.

7. Predicting spatial and temporal shifts in the microbiome

Using information on the drivers of spatial and seasonal variation in the microbiome ((1) to (5) above) we can build mechanistic models to predict future changes in the microbiome, both directly influenced by the abiotic environment, landscape changes and shifts in the host community. Predicting changes in the distribution of microbes that are harmful for crops, domestic animals and humans will be of major interest to policy makers.