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The phylogeny of Colocasiomyia (Drosophilidae) is analysed using data for 70 morphological characters, many of which are re-evaluated from or added to those used previously, for an expanded taxon sample of 24 Colocasiomyia ingroup species. A special focus is put on three species, of which two have remained unresolved for their relationships to other Colocasiomyia species, and the other is a newly discovered species. The analysis results in a single, most parsimonious cladogram, in which a clade comprising the three focal species is recognized along with other clades recovered for the known species groups of Colocasiomyia. Based on this, a new species group—the gigantea group—is established, including Colocasiomyia gigantea (Okada), C. rhaphidophorae Gao & Toda, n.sp. and C. scindapsae Fartyal & Toda, n.sp. These species of the gigantea group breed on inflorescences/infructescences of the subfamily Monsteroideae (Araceae) exceptionally among Colocasiomyia species, most of which use plants of the subfamily Aroideae as their hosts. Colocasiomyia gigantea uses Epipremnum pinnatum (L.) Engler, C. rhaphidophorae uses Rhaphidophora hookeri Schott and C. scindapsae uses Scindapsus coriaceus Engler as their hosts. The host plants of the gigantea group are epiphytes and differ in the structure of spadix and the fruiting process from those of the Aroideae. To understand how the species of the gigantea group adapt to properties of their host plants, their reproductive ecology—most intensively that of C. gigantea—is investigated. The lifecycle of C. gigantea is characterized by its relatively slow embryonic development (taking approximately 6 days), the very long duration of the full-grown first instar within the egg capsule (approximately three months) until dehiscence of host infructescence, and its relatively fast larval and pupal development (taking approximately 11 or 12 days). Some morphological adaptations and the reproductive strategy in terms of ‘egg size vs. number’ trade-off are discussed in relation to their reproductive habits and peculiar lifecycles.

Drosophila liniand its two sibling species,D. ohnishiiandD. ogumai, are hardly distinguishable from one another in morphology. These species are more or less reproductively isolated. The mitochondrialND2andCOI-COIIand the nuclear ITS1-ITS2 regions were sequenced to seek for the possibility of DNA barcoding and to reconstruct the phylogeny of them. The character-based approach for DNA barcoding detected some diagnostic nucleotides only for monophyleticD. ogumai, but no informative sites for the other two very closely species,D. liniandD. ohnishii, of which strains intermingled in the molecular phylogenetic trees. Thus, this study provides another case of limited applicability of DNA barcoding in species delineation, as in other cases of relatedDrosophilaspecies. The molecular phylogenetic tree inferred from the concatenated sequences strongly supported the monophyly of the cluster of the three species, that is, theliniclade. We propose some hypotheses of evolutionary events in this clade.

Despite many studies on the phylogeny of the subgenus Sophophora, its monophyly has not been established, especially in relation to its putative relative, the genus Lordiphosa. We analyzed their phylogenetic relationships using DNA sequence data of two mitochondrial genes (ND2 and COII) and two nuclear genes (Adh and 28SrRNA). In constructing phylogenetic trees, we accounted for the problem of among-taxa nucleotide compositional heterogeneity, and took a sequence-partitioning approach to allow multiple substitution models for nucleotide sequences that have evolved under different evolutionary processes, particularly developing a novel, sequence-partitioning procedure for Neighbor Joining (NJ) tree construction. Trees constructed by different methods showed an almost identical and strongly supported topology in which Sophophora was paraphyletic: Lordiphosa was placed as the sister to the Neotropical Sophophora consisting of the saltans and willistoni groups, and Sophophora was divided into the clade of Lordiphosa + Neotropical Sophophora and the clade of the obscura + melanogaster groups. Based on the estimated time, 45.9 Mya, of divergence between the Old World Lordiphosa and the Neotropical Sophophora and evidence from paleontology, paleo-geography and -climatology, we propose a hypothesis that this vicariant divergence should have occurred when the North Atlantic Land Bridge between Europe and North America broke in the middle Eocene Epoch.

Colocasiomyia, a moderate-sized genus in the subfamily Drosophilinae, comprises seventy (twenty-six described and forty-four undescribed) species. Several Colocasiomyia species have evolved intimate mutualisms with specific host plants, especially of the family Araceae: the flies depend throughout the entire life cycle, oviposition, larval growth, pupation, and adult feeding and mating, on inflorescences of their host plants, and in turn act as species-specific pollinators for their host plants. To understand the evolution of this mutualism between Colocasiomyia flies and their host plants, the phylogenetic relationships of this genus and some possibly related taxa are inferred from a cladistic analysis based on sixty-two characters of adult morphology. We conclude that Colocasiomyia is polyphyletic, with the C. arenga species group clearly separate. Colocasiomyia without the arenga group (Colocasiomyia proper) is sister to all other studied drosophilines, whereas the arenga group is relatively derived within the Drosophilinae. Within Colocasiomyia proper, four clades are recognized, three of which correspond to previously proposed species groups: the cristata, toshiokai and baechlii groups. The other clade, C. sp.1 aff. nepalensis+C. sp.2 aff. nepalensis, is defined as a new species group. Relationships amongst the four clades and three independent species (C. micheliae, C. gigantea and C. sp.K1) remain almost unresolved, except for a sister group relationship between the toshiokai and baechlii groups. The classification of species groups in Colocasiomyia is revised by erecting two new species groups (crassipes and zeylanica groups) in addition to the three known (baechlii, cristata and toshiokai) groups. Revision of the arenga group, which should be removed from Colocasiomyia, is left for future studies. The evolution of host plant selection in Colocasiomyia is discussed by mapping host plant taxa (families, subfamilies and tribes) on the phylogenetic tree deduced from the cladistic analysis. Cohabitation in the same host inflorescence by a pair of species with microallopatric niche separation on the spadix is hypothesized to have evolved independently at least more than twice in Colocasiomyia.

Phylogenetic relationships among the genus Dichaetophora, the genus Nesiodrosophila and the Lordiphosa tenuicauda species-group and some possibly related genera of Drosophilinae were analyzed in this study using 30 morphological characters derived from 34 species. It is concluded that the three taxa constitute a monophyletic group, within which three monophyletic groups are recognized: Dichaetophora + Nesiodrosophila comprise a monophyletic group, while the L. tenuicauda group is divided into two monophyletic groups. This clade is revised as the genus Dichaetophora, with its three constituent monophyletic groups treated as new specis-groups: the agbo, the tenuicauda and the acutissima groups. Nesiodrosophila becomes a junior synonym. A key to the species-groups is provided.

Summary The phylogenetic relationships of Lordiphosa and some taxa in Drosophilinae were analysed on the basis of a total of forty-one selected drosophilid species. These included eighteen species of five Lordiphosa species-groups as the main target, twenty-three species representative of the major drosophiline ingroup taxa and four species of Steganinae as outgroup. Sixty-eight morphological characters of adults were subjected to cladistic analysis. From the results it is concluded that Lordiphosa is polyphyletic; the Lo. tenuicauda species-group and genus Nesiodrosophila form a single monophyletic group; Lordiphosa proper (i.e. Lordiphosa spp. minus the tenuicauda group) comprises another monophyletic group; within Lordiphosa proper the fenestrarum, nigricolor and denticeps groups are all monophyletic, but monophyly of the miki group is not strongly supported; genera Hirtodrosophila and Scaptomyza and subgenus Sophophora are all monophyletic; and within Drosophilinae, genus Scaptodrosophila is the first to have split from the main lineage, but the branching order of other clades, Chymomyza, Lordiphosa proper, Sophophora, Hirtodrosophila, Nesiodrosophila+ Lo. tenuicauda group, Scaptomyza, Dorsilopha and subgenus Drosophila, remains unresolved. The topology of maximum parsimony cladograms suggests that Lordiphosa proper lies close to Sophophora as proposed previously, although its phylogenetic position could not be determined conclusively. By contrast, bootstrap values tended to contradict another hypothesis that Lordiphosa and Scaptomyza are sister groups.

A new species group, the sinensis group, is established within the genus Dichaetophora, based on a phylogenetic analysis of 37 adult morphological characters from 26 drosophilid species, including ten known species of Dichaetophora; four newly described species (Di. abnormis, Di. hainanensis, Di. bicornis, and Di. sinensis spp. nov. from China); and some representatives of related genera (Drosophila, Hirtodrosophila, and Scaptomyza).