Sphecidae, Latreille, 1802

Porto, Diego S., Almeida, Eduardo A. B. & Vilhelmsen, Lars, 2017, Comparative morphology of internal structures of the mesosoma of bees with an emphasis on the corbiculate clade (Apidae: Apini), Zoological Journal of the Linnean Society 179 (2), pp. 303-337 : 303-304

Sphecidae ( Heraty et al., 2011; Klopfstein et al.,

2013) appears to be the sister taxa of bees. Bees comprise approximately 20 000 valid species ( Ascher & Pickering, 2014), among which the genera Apis and Bombus ( Apidae ) are probably the best known taxa. In addition to their species richness, a remarkable diversity of morphologies and social structures is known to exist within Apidae ( Michener, 1974, 2007). The most well-known Apidae are the corbiculate bees ( Apidae : Apinae : Apini ).

The corbiculate bees constitute a conspicuous monophyletic group that differentiated about 75 Mya during the Late Cretaceous ( Cardinal, Straka & Danforth, 2010; Cardinal & Danforth, 2011). The group comprises honey bees (genus Apis ), bumble bees (genus Bombus ), orchid bees ( Aglae , Exaerete , Eufriesea , Eulaema and Euglossa ) and stingless bees (c. 60 genera) ( Rasmussen & Cameron, 2010; Ascher & Pickering, 2014). The clade Apini provides an interesting model for the study of eusociality in bees because it contains representatives with different degrees of social organization, including the only bees that display fixed-caste eusociality (sensu Almeida & Porto, 2014): Apina and Meliponina ( Michener, 1974; Noll, 2002). However, there is still much controversy concerning the evolution of the traits that define totipotent-caste and fixed-caste eusociality in these bee lineages because of contrasting phylogenetic results among the constituent subtribes of Apini , i.e. the ‘corbiculate controversy’ (Chavarr � ıa & Carpenter, 1994; Schultz, Engel & Prentice, 1999; Ascher, Danforth & Ji, 2001; Cardinal & Packer, 2007; Kawakita et al., 2008; Payne, 2013; Almeida & Porto, 2014).

The search for new phylogenetically informative characters from novel sources is of great interest in this context. One important source of such information is internal thoracic morphology. Some comprehensive treatments on this topic include the classical works of Crampton (1909), Snodgrass (1956) and Matsuda (1970), for insects in general, and Snodgrass (1910), Duncan (1939), Heraty, Woolley & Darling (1994) and Vilhelmsen, Miko & Krogmann (2010), for Hymenoptera in particular. Prentice (1991) demonstrated that the shape of the basisternum offers critical evidence that could help elucidate the ‘corbiculate controversy’. Characters derived from the prosternum were first used in phylogenetic analyses of corbiculate bees by Kimsey (1984), later by Prentice (1991), and in a broader context by Roig-Alsina & Michener (1993), Prentice (1998) and Melo (1999).

Another important morphological character system that has been overlooked by morphologists is the complex of the mesofurca/metafurca, consisting of the fused endosternal elements of the meso- and metathorax. This intricate apodemal system has been poorly explored in a comparative manner for bees and seems to be potentially very informative for phylogenetic purposes, as demonstrated for other hymenopteran groups ( Heraty et al., 1994; Vilhelmsen et al., 2010). The mesophragma is also notably interesting, because it is a conspicuous internal sclerite, closely associated with the propodeum, mesoscutellum and 4th axillary sclerite ( Michener, 1944), and appears to offer variation that is congruent with some molecular hypotheses proposed for Apidae (see below).

An extensive morphological comparative study of internal skeletal structures of the mesosoma has never been done before focusing on bees as a whole. The main objective of this work is to explore the comparative morphology of some internal structures (e.g. propectus, mesofurca/metafurca, mesophragma), with special emphasis on representatives of the corbiculate clade ( Apidae : Apini ). Moreover, we attempted to assess the potential of these structures as sources of information to illuminate the phylogenetic relationships within the corbiculate clade. A phylogenetic analysis with the mesosomal dataset was performed, and the information provided by these structures was evaluated contrasting the mapping of character transformations onto alternative published phylogenetic hypotheses.