How ancient are ancient asexuals?
How ancient are ancient asexuals?
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DOI：
10.1098/rspb.2002.2270
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发表时间：
2003-04
期刊：
影响因子：
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通讯作者：
K. Martens;G. Rossetti;D. Horne
中科院分区：
文献类型：
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作者：
K. Martens;G. Rossetti;D. Horne
古代无性繁殖的动物类群，如蛭形轮虫和达尔文介形虫，是研究长期无性繁殖影响的极好模式生物。然而，这些群体完全无性的绝对时间长度大多被忽视了。在达尔文介形虫的例子中，化石记录显示，在二叠纪大灭绝结束后，有性生殖几乎完全消失（约1990年）。2.45亿年前），尽管一些假定的中生代雄性记录模糊了达尔文类动物中专性无性生殖的确切时间框架。在这里，我们重新审视中生代达尔文记录，关于生殖模式的组合。本文用三个标准来区分化石种群中的雄性（无育囊、肌肉疤痕的位置和大小二型性），以检验达尔文虫组合中是否存在雄性。一个大型的，保存完好的组合达尔文豆（福布斯1885）从最新的侏罗纪（约。1.45亿年前）的英格兰被发现在大小和形状上有明显的变化，但结果证明是一个全女性的组合。特殊的保存材料也允许重新分配这个物种的现存达尔文属Alicenula。所有其他假定的二型达尔文记录从中生代重新检查使用相同的标准。这些组合代表两性种群的假设被拒绝为所有后三叠纪（约。20800万年前）的记录。
Ancient asexual animal groups, such as bdelloid rotifers and darwinuloid ostracods, are excellent model organisms to study the effects of long–term asexuality. However, the absolute length of time that these groups have been fully asexual is mostly ignored. In the case of the darwinuloid ostracods, the fossil record shows that sexual reproduction disappeared almost completely after the end of Permian mass extinction (ca. 245 Myr ago), although several putative records of males from the Mesozoic obscure the exact time-frame of obligate asexuality in darwinuloids. Here, we re–examine the Mesozoic darwinuloid records, with regard to the reproductive mode of the assemblages. Three criteria to distinguish males in fossil populations (lack of brood pouch, position of muscle scars and size dimorphism) are used here to test for the presence of males in darwinuloid assemblages. A large, well-preserved assemblage of Darwinula leguminella (Forbes 1885) from the latest Jurassic (ca. 145 Myr ago) of England is found to be markedly variable in size and shape, but nevertheless turns out to be an all female assemblage. The exceptional preservation of the material also allows the re–assignment of this species to the extant darwinuloid genus Alicenula. All other putative dimorphic darwinuloid records from the Mesozoic are re–examined using the same criteria. The hypothesis that these assemblages represent bisexual populations is rejected for all post-Triassic (ca. 208 Myr ago) records.