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.

Corbiculate Bees (Hymenoptera: Apidae): Exploring the Limits of Morphological Data to Solve a Hard Phylogenetic Problem

Corbiculate bees comprise a distinctive radiation of animals including many familiar species, such as honey bees and bumble bees. The group exhibits a broad variety of morphologies and behaviors, including solitary, social, and cleptoparasitic lifestyles. Since corbiculate bees play a critical role for the interpretation of eusocial behaviors, understanding their phylogeny is crucial to explain patterns and mechanisms of social evolution. Despite advances to unveil corbiculate relationships employing genomic data, the drivers of conflict between molecular and morphological hypotheses are still not fully understood. Morphological datasets favor a single origin for highly eusocial behaviors (i.e., Apini + Meliponini) whereas molecular datasets favor other scenarios (e.g., Bombini + Meliponini). Explanations for this incongruence have been suggested, including quality, quantity, and source of data or methodological issues. In this work we tackled this problem by generating the most extensive morphological dataset for the corbiculate bee species by exploring characters from all body regions, including external and internal adult skeletal anatomy. We produced a matrix with 289 characters for 53 taxa of Apidae, including 24 corbiculate bees. We explored different analyses and optimality criteria including extended implied weights parsimony and two partitioning schemes for Bayesian inferences. We contrasted hypotheses with Bayesian topological tests and conducted analyses to investigate if characters were prone to concerted convergence. Our results are congruent with the conclusions of previous studies based on morphology, recovering Apini sister to Meliponini and both of them together sister to Bombini. Finally, we provide our interpretations on the corbiculate controversy and provide a conciliatory scenario about this issue.

Range Expansion of the Cleptoparasitic Orchid Bee Aglae caerulea in the Pantanal of Mato Grosso, Brazil

In the present study, a new occurrence of Aglae caerulea Lepeletier & Audinet-Serville is reported within a few km of the seasonal flooded plain limits of the Pantanal in the Paraguay basin, reinforcing the idea that this species coexists with its hostess Eulaema nigrita, one of the most common species catalogued in several habitats surveyed in the biome. After 18 months of sampling and no A. caerulea male attracted to the baits, methyl cinnamate was added to the set of fragrances available in the field. During four weeks in May and one week in June 2018, a total of 11 males of A. caerulea were attracted to the new bait in the gallery forest of São Vicente Range. With this most recent record, we expand the ranges of occurrence to the north-eastern border of the Pantanal of Barão de Melgaço, in Mato Grosso, Brazil. Future expeditions in the Pantanal of Mato Grosso and Mato Grosso do Sul should record this cleptoparasitic species from southern to western Paraguay river basin, to reduce the biogeographical gaps in this peculiar tribe of corbiculate bees. The cleptoparasitic species A. caerulea may be recorded when adequate field studies and collections are made from the seasonal floodplain habitats to karstic habitats (dry forests) along the Pantanal border.

Temporal changes in the microbiome of stingless bee foragers following colony relocation

ABSTRACT Maintaining beneficial interactions with microbial symbionts is vital for animal health. Yet, for social insects, the stability of microbial associations within and between cohorts is largely unknown. We investigated temporal changes in the microbiomes of nine stingless bee (Tetragonula carbonaria) colonies at seven timepoints across a 10-month period when moved between two climatically and florally different sites. Bacterial 16S rRNA gene and fungal ITS amplicon sequencing confirmed that microbiomes varied considerably between colonies initially at site one. However, following relocation, considerable changes occurred in bacterial community composition within each colony, and the microbiome composition became more similar across colonies. Notably, Snodgrassella disappeared and Zymobacter appeared as relatively abundant taxa. Remarkably, bacterial communities within colonies continued to shift over time but remained similar across colonies, becoming dominated by Acinetobacter six months after returning to the original site. Our results indicate that the stingless bee microbiome can undergo major changes in response to the environment, and that these changes can be long-lasting. Such legacy effects have not been reported for corbiculate bees. Further understanding the microbial ecology of stingless bees will aid future management of colonies used in agricultural production.

Investigating Morphological Complexes Using Informational Dissonance and Bayes Factors: A Case Study in Corbiculate Bees

It is widely recognized that different regions of a genome often have different evolutionary histories and that ignoring this variation when estimating phylogenies can be misleading. However, the extent to which this is also true for morphological data is still largely unknown. Discordance among morphological traits might plausibly arise due to either variable convergent selection pressures or else phenomena such as hemiplasy. Here, we investigate patterns of discordance among 282 morphological characters, which we scored for 50 bee species particularly targeting corbiculate bees, a group that includes the well-known eusocial honeybees and bumblebees. As a starting point for selecting the most meaningful partitions in the data, we grouped characters as morphological modules, highly integrated trait complexes that as a result of developmental constraints or coordinated selection we expect to share an evolutionary history and trajectory. In order to assess conflict and coherence across and within these morphological modules, we used recently developed approaches for computing Bayesian phylogenetic information allied with model comparisons using Bayes factors. We found that despite considerable conflict among morphological complexes, accounting for among-character and among-partition rate variation with individual gamma distributions, rate multipliers, and linked branch lengths can lead to coherent phylogenetic inference using morphological data. We suggest that evaluating information content and dissonance among partitions is a useful step in estimating phylogenies from morphological data, just as it is with molecular data. Furthermore, we argue that adopting emerging approaches for investigating dissonance in genomic datasets may provide new insights into the integration and evolution of anatomical complexes. [Apidae; entropy; morphological modules; phenotypic integration; phylogenetic information.]

Hibernation Leads to Altered Gut Communities in Bumblebee Queens (Bombus terrestris)

Many reptiles, amphibians, mammals, and insects practice some form of hibernation during which their metabolic rate is drastically reduced. This allows them to conserve energy and survive the harsh winter conditions with little or no food. While it can be expected that a reduction in host metabolism has a substantial influence on the gut microbial community, little is known about the effects of hibernation on the composition of the microbial gut community, especially for insects. In this study, we assessed and compared the bacterial gut community composition within the midgut and ileum of indoor-reared queens of Bombus terrestris before and after an artificial hibernation period of 16 weeks. Deep sequencing of 16S ribosomal RNA gene amplicons and clustering of sequence reads into operational taxonomic units (OTUs) at a similarity threshold of 97% revealed several bacterial taxa that are known to be strongly associated with corbiculate bees. Bacterial community composition after hibernation compared to before hibernation was characterized by higher OTU richness and evenness, with decreased levels of the core bacteria Gilliamella (Proteobacteria, Orbaceae) and Snodgrassella (Proteobacteria, Neisseriaceae), and increased relative abundance of non-core bacteria, including several psychrophilic and psychrotrophic taxa.