Evolutionary Ecology of Sex

有性生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，可以为有性生殖提供一般优势（红皇后假说）。T.Yahara通过比较感染有性和无性宿主群体的双病毒宿主范围决定因子orf04的序列差异，利用禽-双病毒系统验证了这一假设。氨基酸替换的频率在有性寄主群体中明显更高，a . sasaki还建立了宿主与寄生虫之间基因对基因相互作用的新模型，表明宿主与寄生虫之间的拮抗性共同进化保存了适应度变异，使有性生殖更加有利。a . kobayashi证明了限制性修饰系统是细菌基因组的寄生虫，并提出了同源重组进化为对抗基因组寄生虫的新假设。本项目的另一个目标是描述一些遗传冲突下的遗传系统，并阐明在遗传传递中利益冲突的遗传元件之间的遗传相互作用的动力学和结果。在有性生殖中，孟德尔遗传是一个规律，但这一规律经常被细胞质遗传因子的自私行为所违背。例如，在Raphanus中，雄性不育是由一个线粒体基因诱导的，但由一个核基因恢复。这种相互作用的结果在现场进行了检验。研究了由微生物侵染引起的赤豆甲虫性别比扭曲系统，证实了赤豆甲虫性别比的完全核控制，尽管微生物侵染率很高。我们还研究了基因组印迹的各种现象。伊瓦萨提出了几个模型，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.