Evolution of Homopterae and Their intracellular Symblonts

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1. This International Scientific Research Program enabled us to work on the ecology of social aphids in detail. We investigated the life cycle of The cabius populimonilis in Colorada and Arizona, U.S.A.In Arizona their life cycle was not associated with migration while in Colorado the life cycle was divided into two, migratory and non-migratory. Analyzes of the individuals in the gall suggested that non-migratory life cycle has evolved secondarily from the migratory one through viviposition by alatae within the gall and apterization of alatae in support of the GP hypothesis by Aoki and Kurosu (1986).2. Except a few specified groups, all the aphid species harbor prokaryotic symbiont in the bacteriocyte. The previous studies demonstrated that aphid, unlike many other insects, does not convert the nitrogen wastes into uric acid, but produces Gln and Asn from the wastes. The amino acids are metabolized by the symbionts to produce essential amino acids for the host. In the present study, we … More demonstrated that planthopper recycles organic nitrogeous compounds in a different manner exploiting its yeastlike symbiont. Planthopper produces uric acid from the wastes and stores it in the tissue, which symbiont metabolizes to produce nitrogenous compounds usable to the host.3. Aphid symbiont, closely related to E.coli, belongs to the gamma3 subdivision of Proteobacteria. It synthesizes selectively a large amount of symbionin, a stress protein homologous to E.Coli GroEL,which functions as molecular chaperone. In the present study, nucleotide sequences encoding symbionins from three closely interrelated aphids were compared with one another and that for GroEL.It was suggested that in these proteins a particular position is highly susceptible to amino acid substitution, through which symbionins, the GroEL homologs symbionts seemed to have acquired a unique function as phosphotransferase on top of the activity as molecular chaperone. This may represent a rare example of non-neutral evolution of molecule under the positive selection pressure. Less