Effects of urban land use gradients on the wild bee microbiome

Bees and their microbes interact in complex networks that allow bees to benefit from symbioses with bacteria and fungi. Microbial composition and abundance affect bee health through immunity, nutrition, and fitness. In everchanging landscapes of urban cities, land use development changes bee habitats and floral resource availability, thus altering the sources of microbes that bees need to establish the microbiome. Here, we implemented metabarcoding of the 16S and ITS regions to characterize the diversity and composition of the bacterial and fungal microbiome in Ceratina calcarata, a small carpenter bee, across urban land use gradients. By categorizing percent land use development, percent green space, annual precipitation, and annual temperature as indicators for urbanization across Toronto, we found that such land use variables can predict microbial diversity. Microbial composition also varied across urban land use gradients, with certain taxa exclusive to rural or urban areas. Environmental features may also lead to different microbe interactions, as co-occurrences between bacteria and fungi varied across urbanization gradients. As surrounding landscapes change the microbial landscape in wild bees and alter the holobiont, urban centres should consider the impact of growing cities on their pollinators’ health and protect wild bees from the effects of anthropogenic activities.