Evolutionary Ecology of Sex

有性繁殖的适应性意义仍不确定。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，可以为有性繁殖提供普遍的优势(红皇后假说)。T.Yahara使用双生病毒系统验证了这一假设，方法是比较双生病毒ORF 04的序列差异，ORF 04是双生病毒的宿主范围决定因素，感染有性和无性宿主群体的病毒之间。A.Sasaki还开发了宿主和寄生虫之间基因对基因相互作用的新模型，表明宿主和寄生虫之间的拮抗协同进化保持了适应度差异，使有性繁殖有利。I.Kobayashi证明了限制-修饰系统是细菌基因组的寄生虫，并提出了一个新的假说，即同源重组是对宝石体寄生虫的反适应进化。该项目的另一个目标是描述一些基因冲突下的遗传系统，并阐明在其传递过程中具有冲突利益的遗传元素之间的遗传相互作用的动力学和结果。在超性生殖下，孟德尔遗传是一种规则，但这一规则经常被细胞质遗传要素的自私行为所违反。例如，在拉帕努斯，男性不育症是由有丝分裂基因诱导的，但由核基因恢复。这种相互作用的结果在实地进行了检验。在微生物感染很高的情况下，对赤小豆甲性比扭曲系统进行了检测，证实了微生物感染对性比的完全核控制，并研究了基因组印迹的各种现象。Y.Iwaa开发了几个模型，可以解释基因组印记的一些独特特性。

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.