Gut microbial diversity in stingless bees is linked to host wing size and is influenced by geography

Stingless bees are globally important social corbiculate bees, fulfilling critical pollination roles in many ecosystems; however, their gut microbiota, especially fungal communities, are not well characterized to date. We collected 121 bee samples from two species, Tetragonula carbonaria and Austroplebeia australis, across a distance of 1,200 km of eastern Australia, and analysed their gut microbiomes. We found that the gut bacterial richness of T. carbonaria was influenced by geography (latitude and longitude) and positively correlated to an established fitness indicator in insects; namely, host forewing length/size that relates to flight capacity of stingless bees. We characterized the core microbiomes of the two bees and found that they consisted of the bacterial taxa Snodgrassella, Lactobacillus, Acetobacteraceae and Bombella, and the fungal taxa Didymellaceae, Monocilium mucidum, Malassezia restricta and Aureobasidium pullulans. Both host species identity and management (wild or managed) significantly influenced the gut microbial diversity and composition, and similarity between colonies declined as the geographical distance between them increased. This result was also supported by our co-existing network analyses. Overall, we have thoroughly analysed stingless bee gut microbiomes, and provided novel evidence that T. carbonaria bees with larger wings or from more southern populations have higher microbial diversity in their guts. Originality-Significance StatementBeneficial interactions between insects and their microbial symbionts are pivotal for their fitness. In this study, we analysed the gut microbiomes of two stingless bee species, Tetragonula carbonaria and Austroplebeia australis, that are widespread and important pollinators in Australia. We characterized their gut microbiomes and detected a significant positive correlation between gut bacterial richness and host forewing size for T. carbonaria; the first time that gut microbial diversity has been linked to a morphological trait in stingless bees. Furthermore, we found that host species identity, management type (wild or managed) and geography all significantly influenced bee gut microbial diversity and composition, and were able to describe both bacterial and fungal core microbial taxa. This study reveals novel understandings of stingless bee gut microbiomes and provides the basis for utilizing microbial strategies to maintain colony health.