全文: "最も近い共通祖先"
7件中 1-7の結果を表示しています
  • 徳田 悠希, 江崎 洋一
    2016年 40 巻 3-8
    発行日: 2016/02/29
    公開日: 2018/03/30
    ジャーナル オープンアクセス
    Marine sessile benthos living on hard substrates have evolved a variety of attachment strategies. Rhizotrochus (Scleractinia, Flabellidae) is a representative of azooxanthellate solitary scleractinians with a wide geographical distribution and unique attachment structures; it firmly attaches to hard substrates using numerous tube-like rootlets, which are extended from a corallum wall. In contrast, most sessile corals, whether extant or extinct, are attached by stereome-reinforced structures at their corallum bases. However, morphological and constructional traits of the rootlets themselves, along with their evolutionary significance, have not yet been fully resolved. Growth and developmental processes of spines in Truncatoflabellum and rootlets in Rhizotrochus suggest that these attachment structures are homologous. Both structures commonly develop from the calicular edges of walls through the transformation of wall structures, and their skeletal microstructures exhibit similar patterns of rapid accretion and thickening deposits. Taking molecular phylogeny and fossil records of flabellids into consideration, Rhizotrochus evolved from a common free-living ancestor and invaded hard-substrate habitats by the exploitation of rootlets originating from spines, which were adaptive for soft-substrates. Repeated evolution of attachment apparatuses in both scleractinian Rhizotrochus and extinct rugosans (e.g., Silurian Dokophyllum) is likely to represent evolutionary convergence. This study of attachment strategies in Rhizotrochus provides new insights into the understanding of not only the history of adaptive strategies of sessile benthos on changing substrates, but also the natures of soft tissues in extinct organisms.
  • 野沢 謙
    1960年 30 巻 6 号 352-357
    発行日: 1960年
    公開日: 2008/03/10
    ジャーナル フリー
    (1) 孤立した単一集団ならば,世代の経過とともにその有効な大きさが指数的に増大する場合,あるいは単一集団が周囲から個体の移入を毎代受け入れでいる場合がそれであるが,人間が繁殖を支配できる家畜においては,
    (2) 幾つかの近交系に対する交配を巡回的に行なつて,生産家畜群を維持する場合には,近交系における近親交配がいかに強度であつても,生産家畜群においては,極限状態でも,ヘテロ性は消失しない.たとえば,近交系が3個以上であれば,近交係数は10%以下に保たれることが明らかになつた.
  • 高畑 尚之
    1988年 28 巻 1 号 16-21
    発行日: 1988/01/25
    公開日: 2009/05/25
    ジャーナル フリー
    The family relationships among a sample of members drawn from a particular generation of populations or species play a central role in describing the genealogical behaviour of generations of individuals. Such a genealogical approach is certainly interesting and important in its own right, but it is also very useful to produce a wide variety of classical results in the mathematical theory of population genetics. The power and elegance of the theory rely on 'equivalence' or 'exchangeability' among individuals in a population and have been best demonstrated in single-locus multiple-allele systems. Here I would like to introduce the basic idea of the theory and some results of its application to molecular taxonomy.
  • 大島 一里
    2015年 65 巻 2 号 229-238
    発行日: 2015/12/25
    公開日: 2016/10/19
    ジャーナル フリー
  • 小島 純一
    2001年 11 巻 1-7
    発行日: 2001/08/20
    公開日: 2018/03/30
    ジャーナル オープンアクセス
  • 佐藤 たまき
    2017年 58 巻 3 号 130-137
    発行日: 2017年
    公開日: 2018/10/29
    ジャーナル フリー



  • 井上 潤, 宮 正樹
    2001年 48 巻 2 号 75-91
    発行日: 2001/11/26
    公開日: 2010/06/28
    ジャーナル フリー
    Higher-level relationships of the basal teleosts are reviewed, with particular reference to the monophyly and interrelationships of the Elopomorpha.Since Greenwood et al. established in 1966 the Elopomorpha on the basis of eight putative synapomorphies, many authors have discussed validity of their monophyly through comparative observations of osteology, ontogeny, microstructure of spermatozoa, and physiology. Such circumstantial evidence have remained controversial, because none of them have reconstructed their phylogeny using character matrices derived from both morphological and molecular data. The same is true of long-standing controversy over phylogenetic positions of the Elopomorpha among major basal teleostean lineages, many authors simply demonstrating their “views” in the form of cladograms with putative synapomorphies until quite recently. Considering their morphological heterogeneity (from very primitive elopomorphs to highly derived eels) and ancient origins that presumably goes back to over a hundred million years ago, we concluded that corroboration of monophyly and determination of the phylogenetic position of the Elopomorpha should be based on comparisons of longer DNA sequences from many purposefully-chosen species. Recent development of a PCR-based approach for sequencing the fish mitochondrial genomes would be the most promising candidate for providing such data within a short period of time and they have actually resolved the latter problem in a recent study.