Intracellular rickettsia-like structures were found in the tissues of a glossiphoniid leech, Torix tagoi, by transmission electron microscopy. Diagnostic PCR analysis using specific primers suggested that of the nine glossiphoniid species examined, two species, T. tagoi and Hemicrepsis marginata, harbored bacteria of the genus Rickettsia. A 1.5-kb eubacterial 16S rRNA gene segment obtained from each of these species was amplified by PCR, cloned, and sequenced. Phylogenetic analysis of the 16S rRNA gene demonstrated that the Rickettsia species found in the leeches constituted a novel clade that is distinct from the clade of arthropod-associated Rickettsia species. In natural populations, 97.7% (43 of 44) of T. tagoi leeches and 100% (9 of 9) of H. marginata leeches carried Rickettsia, suggesting that infection with Rickettsia is prevalent in these leeches. This is the first report of Rickettsia found in annelids.

The genus Pheidole has three distinct castes in females: queen, major, and minor workers. It has been believed that the larvae of major workers have prominent mesothoracic wing discs, although the minor worker larvae lack them. Here we conducted histological examinations of wing discs during larval development in P. megacephala. We show that all three castes have mesothoracic wing discs, at least in their early stage of the final larval instar, and that the wings degenerate differently in the dimorphic worker castes. The minute wing discs of minor workers neither grow nor metamorphose but disappear during the prepupal stage. On the contrary, the wing discs of major workers evaginate at the onset of the prepupal stage but subsequently degenerate by apoptotic cell death. This apoptotic wing degeneration in the prepupal stage was contradistinguished from wing degeneration in some lepidopteran insects, in which apoptosis occurs in the pupal wing buds. Our results suggest that each worker caste shows a different degeneration process to express the wingless character and that apoptotic degeneration has been adopted in association with the evolution of worker dimorphism.

Some Formicid ants have symbiotic intracellular bacteria in the epithelial cells of their midgut. These endosymbionts are believed to be derived from a common ancestor. A recent study revealed that endosymbionts of the ant genus Camponotus are closely related to Enterobacteriaceae, but their relationship to endosymbionts of other genera of ants is unknown. In this study, the nucleotide sequences of 16S ribosomal RNA (rRNA) of endosymbionts and mitochondrial cytochrome oxidase subunit I (COI) of their host were determined in five genera of the subfamily Formicinae (Hymenoptera: Formicidae). Based on these molecular data, we constructed phylogenetic trees in order to characterize the systematic position of the symbionts and to estimate the relationship of symbionts and hosts. The analysis showed that the endosymbionts were all connected with the Enterobacteriaceae but did not constitute a monophylitic group, while the three genera belonging to the tribe Camponotini, the endosymbionts and their hosts made a clade. The topologies of these trees were identical for the most part. These results suggest that the endosymbionts of ants have plural origins, and that in the Camponotini, ancestral symbionts have coevolved with their host ants, which are so divergent to several genera as to construct one tribe

We here show an example of morphological novelties, which have evolved from insect wings into the specific structures controlling social behaviour in an ant species. Most ant colonies consist of winged queen(s) and wingless workers. In the queenless ponerine ant Diacamma sp. from Japan, however, all female workers have a pair of small thoracic appendages, called "gemmae", which are homologous to the forewings and acts as an organ regulating altruism expression. Most workers, whose gemmae are clipped off by other colony members, become nonreproductive helpers, while only a single individual with complete gemmae becomes functionally reproductive. We examined histologically the development of gemmae, and compared it with that of functional wings in males. Female larvae had well-developed wing discs for both fore- and hindwings. At pupation, however, the wing discs started to evaginate and later degenerate. The hindwing discs completely degenerated, while the degeneration of forewing discs was incomplete, leading to the formation of gemmae. The degeneration process involved apoptotic cell death as confirmed by TUNEL assay. In addition, glandular cells differentiated from the epithelial cells of the forewing buds after completion of pupation. The mechanism of developmental transition from wing to gemma can be regarded as an evolutionary gain of new function, which can be seen in insect appendages and vertebrate limbs.