Abstract

Diversification of species is one of the oldest issues in biology dating back to Darwin, and many biologists then have tried to gain insight through population genetics and molecular biology. We investigated two topics to understand speciation of Drosophila, which are sex-ratio distortion (SR) and genetic diversification at genomic level. SR is one of the forms of non-Mendelian segregation possibly underlying reproductive isolation and speciation in some species of Drosophila. To investigate the mechanism of suppression in two novel cases of SR in D. simulans, we conducted microarray experiments with the too much yin (Tmy) and not much yang (Nmy) suppressors. We found 61 genes that are differentially expressed in mutants compared with wild type. We then compared the sequence structures of Tmy and Nmy against the whole Drosophila genome, and found a possible regulatory element that may regulate some of these 61 genes. This result estimates the gene expression network that underlies SR suppression in Drosophila. For the analyses of genomic diversification in Drosophila, we investigated genomic changes with speciation of seven Drosophila species and discuss how diversification has occurred through these changes. From the genomic data of seven Drosophila species, we identified 9916 gene clusters that are shared by at least two species. Identifying orthologous genes by means of phylogenetic analyses of these clusters, we examined lineage specific expansions (LSE), rapidly evolved genes (RE), and loss of genes (GL) in each species. One interesting finding is that, in the LSE , there are many genes corresponding to gene ontology categories “response to stimulus” or “morphogenesis”, which might play a role in adaptation to a new or changing environment. These analyses suggest that Drosophila species have complex mechanisms of genomic diversification perhaps reflecting adaptation to changes in their environment.