Evolutionary Ecology of Sex

有性生殖的适应意义仍然不确定。这个项目的目的之一就是解开这个谜团。病原体驱动的选择被认为是一个可能的因素，可以提供一个一般的优势，有性生殖（红皇后假说）。T.Yahara利用泽兰-双生病毒系统，通过比较感染有性和无性宿主群体的病毒之间双生病毒的宿主范围决定因子ORF 04的序列差异，验证了这一假设。氨基酸替换的频率在性宿主种群中显著较高，A.Sasaki还提出了一个新的宿主和寄生虫之间基因对基因相互作用的模型，并表明宿主和寄生虫之间的拮抗性协同进化保护了适合度变异，使有性繁殖有利。I.小林证明了限制性-修饰系统是细菌基因组的寄生虫，并提出了一个新的假设，即同源重组是作为一种反该项目的另一个目标是描述遗传冲突下的一些遗传系统，并阐明遗传冲突的动态和结果。遗传因素之间的遗传相互作用，在它们的传播中具有相互冲突的利益。在有性生殖中，孟德尔遗传是一条规则，但这条规则经常被细胞质遗传元件的自私行为所破坏。例如，萝卜属的雄性不育是由线粒体基因诱导的，但由核基因恢复。在实地审查了这种互动的结果。对由微生物感染引起的红豆甲虫性比畸变系统进行了研究，确认了尽管微生物感染很严重，但性比仍由核控制。同时，还研究了基因组印记的各种现象。Y.Iwasa开发了几种模型，可以解释基因组印迹的一些独特性质。

Adaptive significance of sexual reproduction remains uncertain. One of the purposes of this project was to unravel this mystery. Pathogen-driven selection has been regarded as a likely factor that can provide a general advantage for sexual reproduction (Red Queen hypothesis). T.Yahara tested this hypothesis using Eupatorium-geminivirus system by comparingsequence divergence of ORF 04, a host-range determinant of geminivirus between viruses infecting sexual and asexual host populations. Frequency of amino acid replacements was significantly higher in sexual host populations, supporting the hypothesis.A.Sasaki also developed a new model for gene-for-gene interactions between hosts and parasites and showed that antagonistic coevolution between hosts and parasites conserve fitness variation and make sexual reproduction advantageous.I.Kobayashi demonstrated that restriction-modification systems are parasites of bacterial genome and developed a new hypothesis that homologous recombination evolved as an counter-adaptation against gemomic parasites.Another target of this project was to describe some genetic systems under genetic conflicts and elucidate dynamics and outcomes of genetic interactions between genetic elements with conflicting interests in their transmission. Under suxual reproduction, Mendelian inheritance is a rule, but this rule is often violated by selfish behaviours of cytoplasmic genetic elements. In Raphanus, for example, male sterility is induced by a mitocondrial gene, but is restored by a nuclear gene. Outcomes of this interaction was examined in the field. Sex ratio distortion system in azuki-bean beetles, that is caused by Infection of microorganisms, was examined and complete nuclear control of sex ratio was confirmed in spite that infection of microorganism was very high.We also studied various phenomena of genomic imprinting. Y.Iwasa developed several models which can explain some unique properties of genomic inprinting.