Bee morphology: A skeletomuscular anatomy of Thyreus (Hymenoptera: Apidae)

Although the knowledge of the skeletal morphology of bees has progressed enormously, a corresponding advance has not happened for the muscular system. Most of the knowledge about bee musculature was generated over 50 years ago, well before the digital revolution for anatomical imaging, including the application of microcomputed tomography. This technique, in particular, has made it possible to dissect small insects digitally, document anatomy efficiently and in detail, and visualize these data three dimensionally. In this study, we document the skeletomuscular system of a cuckoo bee, Thyreus albomaculatus and, with that, we provide a 3D atlas of bee skeletomuscular anatomy. The results obtained for Thyreus are compared with representatives of two other bee families (Andrenidae and Halictidae), to evaluate the generality of our morphological conclusions. Besides documenting 199 specific muscles in terms of origin, insertion, and structure, we update the interpretation of complex homologies in the maxillolabial complex of bee mouthparts. We also clarify the complicated 3D structure of the cephalic endoskeleton, identifying the tentorial, hypostomal, and postgenal structures and their connecting regions. We describe the anatomy of the medial elevator muscles of the head, precisely identifying their origins and insertions as well as their homologs in other groups of Hymenoptera. We reject the hypothesis that the synapomorphic propodeal triangle of Apoidea is homologous with the metapostnotum, and instead recognize that this is a modification of the third phragma. We recognize two previously undocumented metasomal muscle groups in bees, clarifying the serial skeletomusculature of the metasoma and revealing shortcomings of Snodgrass' "internal-external" terminological system for the abdomen. Finally, we elucidate the muscular structure of the sting apparatus, resolving previously unclear interpretations. The work conducted herein not only provides new insights into bee morphology but also represents a source for future phenomic research on Hymenoptera.

Total-evidence dating and morphological partitioning: a novel approach to understand the phylogeny and biogeography of augochlorine bees (Hymenoptera: Apoidea)

Augochlorini comprise 646 described bee species primarily distributed in the Neotropical region. According to molecular and morphological phylogenies, the tribe is monophyletic and subdivided into seven genus groups. Our main objective is to propose a revised phylogeny of Augochlorini based on a comprehensive data set including fossil species as terminals and new characters from the internal skeleton. We also aim to develop a total-evidence framework incorporating a morphological-partitioned homoplasy approach and molecular data and propose a detailed biogeographic and evolutionary scenario based on ancestor range estimation. Our results recovered Augochlorini and most genus groups as monophyletic, despite some uncertainties about monophyly of the Megalopta and Neocorynura groups. The position of the cleptoparasite Temonosoma is still uncertain. All analyses recovered Augochloropsis s.l. as related to the Megaloptidia group. Internal characters from the head, mesosoma and sting apparatus provided important synapomorphies for most internal nodes, genus groups and genera. Augochlorini diversification occurred in the uplands of the Neotropical region, especially the Brazilian Plateau. Multiple dispersals to Amazonia, Central America and North America with returns to the Atlantic endemism area were recovered in our analysis. Total evidence, including morphological partitioning, was shown to be a reliable approach for phylogenetic reconstruction.

Comparative morphology and evolution of the cranial musculature in bees (Hymenoptera: Apoidea)

Comparative morphological studies in bees are mostly restricted to the skeleton, and the musculature of bees has not been explored much from this perspective. Here we investigate the head extrinsic musculature under an evolutionary perspective. The musculature of 34 bee species belonging to six major lineages and 26 tribes plus two apoid wasps is described, illustrated, and compared. A standardized terminology for the extrinsic musculature is proposed and aligned with the Hymenoptera Anatomy Ontology (HAO). A total of 12 characters derived from the analysis were optimized onto a summary phylogenetic tree. The musculature was found to be conserved among the main bee lineages, and most variation was found in the proboscis; no modification was found in antennal muscles. Four characters are interpreted as synapomorphies for bees, one for the long-tongued bees, three for Halictinae, and one for Megachilinae. We also found that the Apinae clade of cleptoparasites is supported by some character state transformations and that stingless bees have a unique posterior fronto-pharyngeal muscle. Both sexes display similar morphology, except for having two fixed attachment points for the anterior cranio-mandibular muscle in the males of Andreninae. This study provides a foundation for future investigations on bee head musculature on various taxonomic levels.