The precise position of the replication origin (O R ) of mtDNA was determined for insect species belonging to four different orders (four species of Drosophila, Bombyx mori, Triborium castaneum, and Locusta migratoria, which belong to Diptera, Lepidoptera, Coleoptera, and Orthoptera, respectively). Since the free 59 ends of the DNA strands of mtDNA are interpreted as the O R , their positions were mapped at 1-nucleotide resolution within the A 1 T-rich region by using the ligation-mediated PCR method. In all species examined, the free 59 ends were found within a very narrow range of several nucleotides in the A 1 T-rich region. For four species of Drosophila, B. mori, and T. castaneum, which belong to holometabolous insects, although the O R 's were located at different positions, they were located immediately downstream of a series of thymine nucleotides, the so-called T-stretch. These results strongly indicate that the T-stretch is involved in the recognition of the O R of mtDNA at least among holometabolous insects. For L. migratoria (hemimetabolous insect), on the other hand, none of the long stretches of T's was found in the upstream portion of the O R , suggesting that the regulatory sequences involved in the replication initiation process have changed through insect evolution.

Sexual dimorphism is often derived from sexual selection. In sexually dimorphic Drosophila species, exaggerated male structures are used for specific behaviors in male-to-male competition or courtship toward females. In Drosophila prolongata, a member of the melanogaster species group, males have enlarged forelegs whereas females do not. However, the adaptive role of the enlarged forelegs is unclear because little is known about the behavior of D. prolongata. In this study, the courtship behavior of D. prolongata was investigated in comparison with closely related species. Males of D. prolongata use their forelegs in a specific behavior, ''leg vibration'', in which the male vigorously vibrates the female's abdomen by extending his forelegs from in front of her. Leg vibration was observed immediately before ''attempting copulation'', indicating that it has an adaptive role in the mating process. In contrast, leg vibration was not observed in closely related species. Because the large forelegs are necessary to accomplish leg vibration, it was suggested that the sexual dimorphism of D. prolongata forelegs is currently under the influence of sexual selection in courtship behavior.

We analyzed the phylogenetic relationship between the species of Lordiphosa and other Drosophilidae using alcohol dehydrogenase (Adh) gene sequences. The phylogenetic trees consistently show that the four species Drosophila kurokawai, D. collinella, D. stackelbergi, and D. clarofinis, which include three species groups of Lordiphosa, form a monophyletic clade. This clade is placed as a sister group to the willistoni and saltans groups of Sophophora. On the other hand, three species of Lordiphosa, D. tenuicauda, D. pseudotenuicauda, and D. acutissima, all of which belong to the tenuicauda group, are not shown to be related to the major Lordiphosa lineage. In the phylogenetic trees, these species are included into the clade comprised of Drosophila and Hirtodrosophila, although it remains uncertain whether the tenuicauda group is a monophyletic group or not. These results indicate that Lordiphosa is polyphyletic and that most of the members of the subgenus have a close relationship to the neotropical groups of Sophophora. The above conclusion is compatible with the hypothesis of Okada (Mushi [1963] 37:79-100) and Lastovka and Máca (Acta Ent Bohemoslov [1978] 75:404-420) that Lordiphosa is most closely related to Sophophora; in contrast, our results contradict the hypothesis of Grimaldi (Bull Am Mus Nat Hist [1990] 197:1-139) that Lordiphosa is a sister group to the genus Scaptomyza.

Background: Species of the Drosophila obscura species group (e.g., D. pseudoobscura, D. subobscura) have served as favorable models in evolutionary studies since the 1930's. Despite numbers of studies conducted with varied types of data, the basal phylogeny in this group is still controversial, presumably owing to not only the hypothetical 'rapid radiation' history of this group, but also limited taxon sampling from the Old World (esp. the Oriental and Afrotropical regions). Here we reconstruct the phylogeny of this group by using sequence data from 6 loci of 21 species (including 16 Old World ones) covering all the 6 subgroups of this group, estimate the divergence times among lineages, and statistically test the 'rapid radiation' hypothesis.

BackgroundThe hippolytid genus Lysmata is characterized by simultaneous hermaphroditism, a very rare sexual system among Decapoda. Specialized cleaning behavior is reported in a few pair-living species; these life history traits vary within the genus. Unfortunately, the systematics of Lysmata and the Hippolytidae itself are in contention, making it difficult to examine these taxa for trends in life history traits. A phylogeny of Lysmata and related taxa is needed, to clarify their evolutionary relationships and the origin of their unique sexual pattern. In this study, we present a molecular phylogenetic analysis among species of Lysmata, related genera, and several putative hippolytids. The analysis is based upon DNA sequences of two genes, 16S mtDNA and nuclear 28S rRNA. Phylogenetic trees were estimated using Bayesian Inference, Maximum Likelihood, and Maximum Parsimony.ResultsPhylogenetic analysis of 29 species of Lysmata, eight genera of Hippolytidae and two genera of Barbouriidae based on a single (16S, 28S) and combined gene approach (16S+28S) indicates that three groups of Lysmata differentiate according to antennular morphology: (1) Lysmata, having a multi-segmented accessory branch, (2) Hippolysmata (prior to Chace 1972), with a one-segmented accessory branch, and (3) a third group of Lysmata outliers, with one-segmented unguiform accessory branch, and close affinity to the genera Exhippolysmata and Lysmatella. The monophyly of the clade bearing a multi-segmented accessory branch is robust. Within the short accessory branch clade, species with specialized cleaning behaviors form a monophyletic clade, however, the integrity of the clade was sensitive to alignment criteria. Other hippolytid and barbouriid genera used in the analysis are basal to these three groups, including one displaying simultaneous hermaphroditism (Parhippolyte). The two barbouriid species occur in a separate clade, but among hippolytid taxa.ConclusionsThe data support the historical morphological division of Lysmata into clades based on accessory branch morphology. The position of the "cleaner" shrimps, indicates that specialized cleaning behavior is a derived trait. The topologies of the cladograms support the monophyly of the barbouriids, but do not support their elevation to familial status. Taxa ancestral to the genus Lysmata display simultaneous hermaphroditism, suggesting that this life history trait evolved outside the genus Lysmata.

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