Scuttling towards monophyly: phylogeny of the mega-diverse genus Megaselia (Diptera: Phoridae)

The genusMegaseliaRondani (Diptera: Phoridae) is one of the largest in the animal kingdom, with nearly 1700 described species and many remaining to be discovered. Work on this group is notoriously challenging due to the extreme species diversity, poor knowledge of higher-level relationships and lack of molecular data. In this paper, we present the largest study to date ofMegaseliarelationships based on molecular data from one nuclear (28S rDNA) and three mitochondrial (ND1, COI and 16S) markers for 175 Nordic specimens representing 145 species ofMegaselia, plus outgroups. Based on phylogenetic analyses of these data, we propose 22 informalMegaseliaspecies groups, all of which match well-supported terminal clades. Relationships among these groups, and between them and several isolated species, remain largely uncertain. Of the 22, 20 species groups fall into a moderately well-supported monophyletic clade of 'coreMegaselia'. Two species groups, thespinigeraandruficornisgroups, fall outside of coreMegaselia, as does the single representative ofMyriophora, a genus that is included inMegaseliaby some specialists. Here, we explore the morphology of these molecular species groups to aid future studies, and we discuss the implications of our findings for the generic circumscription ofMegaselia. Hopefully, our results can aid further characterization of subgroups within the enormousMegaseliaradiation and among its closest relatives, thus facilitating future work on this challenging but fascinating group of small flies.