Population dynamics of notothenioid fishes. - Examination of adaptive evolution and neutral evolution -

在本项目中，背银鱼类抗冻糖肽的起源被估计为大约2180 - 2430万年前，这对应于背银鱼类、掠夺鱼类、龙鱼类和冰鱼类，Near等人（2006）最近发现，一种冰鱼保留了α珠蛋白基因，而其他15种冰鱼则没有，并怀疑至少两种单倍型在冰鱼中共存。冰鱼物种连续出现的时期。一个大的有效人口规模预计两个假基因单倍型将保持中立数百万年，但各种估计的有效人口规模推断几个现有的物种从mtDNA多态性（几十万到数百万）几乎是人口的最低有效规模来解释这种情况。考虑到所研究的大多数物种可能都经历了最近的种群扩张，并且对冰鱼α血红蛋白基因检测到明显的正选择，推测某种类型的选择在过去的很长一段时间内保持了等位假基因。在主要组织相容性复合体基因II类β基因上检测到个体间的核苷酸序列变异，表明该物种过去的种群规模较大。对于免疫球蛋白基因，核苷酸重复导致蛋白质结构的快速变化，就像抗冻糖肽一样，这提出了基因和核苷酸重复在背索线虫基因组进化中发挥重要作用的可能性。

In this project, the origin of antifreeze glycopeptides of notothenioid fishes was estimated to be about 21.8-24.3 million years ago, which corresponded to the time when fishes of notothens, plunderfishes, dragonfishes, and icefishes, were about to be diverged.Near et al. (2006) have recently identified that one species of icefish has retained alpha globin gene but not other 15 species of icefishes and have suspected that at least the two haplotypes had coexisted for the period of successive icefish speciations. A large effective population size is expected for two pseudogene haplotypes to be maintained neutrally for millions of years but various estimates of effective population size inferred for several existing species from mtDNA polymorphism (several hundred thousands to millions) are barely the minimum effective size of population to account for the situation. Considering that the most species studied have likely been subject to recent population expansion and that apparent positive selection is detected for the icefish alpha hemoglobin gene, some type of selection is speculated to maintain allelic pseudogenes for prolonged period in the past.Despite of limited nucleotide diversity of mitochondrial gene observed for Antarctic toothfish Dissostichus mawsoni, nucleotide sequence variation among individuals is detected at major histocompatibility complex gene class II beta genes, indicating larger population size of the species in the past. For the immunoglobulin gene, nucleotide duplication has caused rapid change of protein structure as in the case of antifreeze glycopeptides and it raised possibility that gene and nucleotide duplications have played significant roles in the evolution of notothenioid genome.