Molecular phylogenetic study on genes related to sperm packets in the Volvocaceae (Chlorophyta)

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In order to analyze the phylogenetic position of evolution of sperm packets in the colonial families Volvocaceae and Goniaceae, phylogenetic relationships within these families were inferred based on the cladistic analysis of the morphological data. The strict consensus tree of this analysis indicated that sperm packets evolved in a Yamagishiella-like isogamous alga to give rise to a monophyletic group comprising the anisogamous/oogamous genera Eudorina, Platydorina, Pleodorina and Volvox. Furthermore, phylogenetic analysis based on the rbcL gene sequence data suggested, with high bootstrap values, the presence of a monophyletic group composed of almost all the members of the anisogamous/oogamous volvocacean species, in which Eudorina elegans was resolved as the most primitive species. It is, therefore, suggested that the genes related to the sperm packets of E.elegans is most primitive within the anisogamous/oogamous group. Thus is may be fruitful to compare such genes of Eudorina and homologous genes of Yamagishiella in order to study the evolution of genes related to sperm packets.As the first step to study the evolution of Eudorina genes related to sperm packets from genes in a Yamagishiella-like alga, isolation of genes related to sperm packets in E.elegans based on differential screening methods seemed to be essential. Therefore, methods to induce sperm packets in a large volume of E.elegans culture were established. Approximately 20% of cultured cells were induced to develop into sperm packets by using an incubator (25ﾟC) and a large flask containing Pleodorina mating medium (Nozaki et al., Phycologia 28 : 252-267,1989) continuously aerated. Comparative analyzes of mRNA extracted from the induced sperm packets and vegetative cells will resolve the phylogenetic characteristics of the genes related to sperm packets.