Developmental microbiome of the small carpenter bee, Ceratina calcarata

Abstract

The importance of the holobiont has been studied across many bee species, but less is known about the changes in the microbiome throughout the course of development, particularly in subsocial bees. This study used 16S rRNA and ITS amplicon sequencing of pollen provisions and individuals of the small carpenter bee, Ceratina calcarata, across stages of development to characterize the composition and diversity of bacteria and fungi in the microbiome. Pollen provisions and larval stages showed similar beta diversity, but differences in taxa composition. There was no significant decrease in diversity during the transition between larval and pupal stages that was expected post defecation. However, there were unexpected and progressive declines in diversity as development progressed from the early to late pupal stages and again from the callow to adult stages. Bees across all stages lacked members of the Lactobacillus (now Apilactobacillus) genus, which has been shown in other studies to be part of the core bacterial community in C. calcarata and all bees. Three correlations between bacteria and fungi were found, suggesting common beneficial bacteria may protect the bees from prevalent fungal pathogens. Low alpha diversity, particularly in the later stages of development through adulthood, is concerning as the microbiome plays an important role in maintaining wild bee health.

The effects of urban land use gradients on wild bee microbiomes

“…On the contrary, the two fungal genera found in high abundance in more rural areas, Ascosphaera and Taphrina, are facultative bee and plant pathogens, respectively, (Cissé et al, 2013;Wynns et al, 2013). However, these genera were also previously seen in immature C. calcarata and it is unclear if they pose any threat to this species (Nguyen and Rehan, 2022). Ascosphaera was also overrepresented at high and very high development levels (Supplementary Table S4; Figure 4B), suggesting this fungi may not be limited to rural areas.…”

“…Apilactobacillus are common beneficial bee symbionts (Tlais et al, 2022) and were established as part of the core microbiome in C. calcarata in New Hampshire, a more rural landscape (McFrederick and Rehan, 2016;Graystock et al, 2017). In urban cities such as Toronto, Apilactobacillus was previously largely absent in adult C. calcarata (Nguyen and Rehan, 2022) and was found to be underrepresented at sites with moderate levels of land use development, overrepresented in sites with the most green space, and overrepresented at sites with lower annual temperatures in this study (Supplementary Table S4). Thus, urban bees reveal a different microbiome from those in rural contexts and of particular concern is the varying abundance of Apilactobacillus.…”

“…Bacteria of the genus Sphingomonas have been shown to be negatively correlated with Fusarium species that cause Fusarium Head Blight in maize crops (Cobo-Díaz et al, 2019). In C. calcarata, Sphingomonas co-occurred positively with the fungal genera Pantoea (Nguyen and Rehan, 2022), a genus prevalent in C. australensis (Shell and Rehan, 2022), A. mellifera (Wright et al, 2001), and stingless bees (Leonhardt and Kaltenpoth, 2014). Additionally, Sphingomonas is a dominant bacteria found in the nests of stingless bees Frieseomelitta varia, Melipona quadrifasciata, and Tetragonisca angustula (de Sousa, 2021) and is also found in A. mellifera (Anjum et al, 2018;Muñoz-Colmenero et al, 2020) and O. bicornis microbiomes (Mohr and Tebbe, 2006), thus this bacteria co-occurs naturally with wild bees.…”

“…For solitary wild bees, this research is in its infancy; however, it is known that wild bees do not always maintain the same consistent core microbiome seen in social bees ( McFrederick et al, 2012 , 2014 ; Kwong and Moran, 2016 ; McFrederick and Rehan, 2016 ; Graystock et al, 2017 ). An example on how solitary wild bees can have differing core microbiomes can be found in C. calcarata , a wild bee displaying different core microbiomes from other bee species and across different regions ( Graystock et al, 2017 ; Dew et al, 2020 ; Nguyen and Rehan, 2022 ; Shell and Rehan, 2022 ).…”

“…A range of variables, including developmental stage ( McFrederick et al, 2014 ; Kapheim et al, 2021 ; Nguyen and Rehan, 2022 ), sociality of host species ( Mohr and Tebbe, 2006 ; McFrederick et al, 2014 ; Graystock et al, 2017 ), climate ( McFrederick and Rehan, 2019 ), geographical location ( Almeida et al, 2022 ), and landscape features ( Cohen et al, 2020 ), have been examined to determine their effects on the microbiome. Examining microbiomes across host developmental stages has allowed for closer examinations of the establishment of microbes, showing that diet is the main source of bacteria and fungi for developing solitary bees ( Dew et al, 2020 ; Pozo et al, 2020 ; Kapheim et al, 2021 ; Nguyen and Rehan, 2022 ). Sociality can influence the bee microbiome by impacting how solitary and social bees interact with food resources, the environment, and other bees to transmit different microbes ( Mohr and Tebbe, 2006 ).…”