| dc.description.abstract | Using a cladistic analysis of adult external morphological characters, I first explore the relationships of the tribes in the bee subfamily Megachilinae. Next, I examine the phylogeny of the subgenera of Megachile s. l., and propose a phylogeny-based classification for the genus. This cosmopolitan genus is the largest in the family Megachilidae, which includes economically important species used in crop pollination. The more than 2000 species of Megachile s. l. are controversially grouped in 58 subgenera, including a fossil from Dominican amber. Most subgenera have not been revised and many species have not been properly associated with any of the known subgenera. In the phylogenetic analysis of Megachiline tribes, I analyzed 110 characters and selected three outgroups and 38 species (24 genera) of informal generic groups traditionally recognized. In the phylogenetic analysis of Megachile s. l., I analyzed 231 characters and used ten outgroup species and 103 ingroup species (53 subgenera). All five tribes currently recognized in Megachilinae were recovered. Lithurgini was the sister group of all other tribes; no synapomorphies were found for Osmiini, and all tribes appeared monophyletic. The cleptoparasitic bee tribe, Dioxyini, was the sister group of the clade formed by Anthidiini, and Osmiini + Megachilini. A single putative synapomorphy (sixth tergum of male with a transverse preapical carina) supported the monophyly of Megachilini. In the phylogenetic analysis of Megachile, the cleptoparasitic genera, Coelioxys and Radoszkowskiana, were the sister group of Megachile. Within Megachile s. l., most subgenera fall into morphological groups previously associated with differences in nesting behavior. Basal branches included subgenera that use mud or resins as nesting materials (traditionally placed in the genus Chalicodoma), whereas a large, more derived clade contained the subgenera Creightonella, Megella, and Mitchellapis, and those groups with flattened abdomen and female mandibles with cutting edges (i.e., leaf-cutter bees). The phylogenetic position of the cleptoparasitic tribe Dioxyini, as sister group of the remaining Megachilinae, supports the distinctness of these bees from other members of the subfamily. It also suggests that those characters shared with Anthidiini, frequently used to place it within that tribe, are likely homoplasies. Further studies including molecular characters and critical taxa that posses a mixture of tribal features, such as the anthidine Aspidosmia, will test the sister group relationship of Osmiini + Megachilini. I discuss the monophyly of the subgenera of Megachile s. l. and propose alternative classifications that are more morphologically and behaviorally meaningful. I also discuss the evolution of some morphological traits correlated with female nesting behavior and geographical distribution of the subgenera of Megachile s. l. | |
