Urbanization reduces gut bacterial microbiome diversity in a specialist ground beetle, Carabus convexus.

Urbanization is rapidly shaping and transforming natural environments, creating networks of modified land types. These urbanization-driven modifications lead to local extinctions of several species, but the surviving ones also face numerous novel selection pressures, including exposure to pollutants, habitat alteration, and shifts in food availability and diversity. Based on the assumption that the environmental pool of microorganisms is reduced in urban habitats due to habitat alteration, biodiversity loss, and pollution, we hypothesized that the diversity of bacterial microbiome in digestive tracts of arthropods would be lower in urban than rural habitats. Investigating the gut bacterial communities of a specialist ground beetle, Carabus convexus, in forested rural versus urban habitats by next generation high-throughput sequencing of the bacterial 16S rRNA gene, we identified 3839 bacterial amplicon sequence variants. The composition of gut bacterial samples did not significantly differ by habitat (rural vs. urban), sex (female vs. male), sampling date (early vs. late spring), or their interaction. The microbiome diversity (evaluated by the Rényi diversity function), however, was higher in rural than urban adults. Our findings demonstrate that urbanization significantly reduced the diversity of the gut bacterial microbiome in C. convexus.