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Copulation in antiarch placoderms and the origin of gnathostome internal fertilization

机译:反弓虫编结的交配和gnathostome内部受精的起源

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摘要

Reproduction in jawed vertebrates (gnathostomes) involves either external or internal fertilization1. It is commonly argued that internal fertilization can evolve from external, but not the reverse. Male copu-latory claspers are present in certain placoderms, fossil jawed vertebrates retrieved as a paraphyletic segment of the gnathostome stem group in recent studies. This suggests that internal fertilization could be primitive for gnathostomes, but such a conclusion depends on demonstrating that copulation was not just a specialized feature of certain placoderm subgroups. The reproductive biology of antiarchs, consistently identified as the least crownward placoderms and thus of great interest in this context, has until now remained unknown. Here we show that certain antiarchs possessed dermal claspers in the males, while females bore paired dermal plates inferred to have facilitated copulation. These structures are not associated with pelvic fins. The clasper morphology resembles that of ptyctodonts, a more crown-ward placoderm group, suggesting that all placoderm claspers are homologous and that internal fertilization characterized all placoderms. This implies that external fertilization and spawning, which characterize most extant aquatic gnathostomes, must be derived from internal fertilization, even though this transformation has been thought implausible. Alternatively, the substantial morphological evidence for placoderm paraphyly must be rejected.
机译:颌骨脊椎动物(咬足动物)的繁殖涉及外部或内部受精1。人们普遍认为,内部受精可以从外部演变而来,而不是相反。在最近的研究中,雄性共产共生的claspers存在于某些编轴器中,这些颚化石为脊椎动物,是作为gnathostome茎组的副生部分恢复的。这表明内部受精可能是咬虫的原始方法,但是这一结论取决于证明交配不仅仅是某些编轴器亚组的特殊特征。一直以来,Antiarch的生殖生物学一直被认为是最没有冠状的鞭毛虫,因此在这种情况下引起了极大的兴趣,至今仍未知。在这里,我们显示某些antiarch男性中具有真皮claspers,而女性则具有成对的真皮板,后者被推断为有助于交配。这些结构与骨盆鳍无关。 clasper的形态类似于冠状头齿编组的ptyctodonts的形态,表明所有placoderm claspers都是同源的,并且内部受精是所有placoderms的特征。这意味着表征大多数现存的水生动物寄养动物的外部受精和产卵必须来自内部受精,即使这种转化被认为是不可行的。或者,必须拒绝关于副鞭毛的实质形态学证据。

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  • 来源
    《Nature》 |2015年第7533期|196-199|共4页
  • 作者单位

    School of Biological Sciences, Flinders University, 2100, Adelaide, South Australia 5001, Australia,Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, California 9007,USA,Museum Victoria, PO Box 666, Melbourne, Victoria 3001, Australia;

    Institute of Geology at Tallinn University of Technology, Ehitajate tee 5,19086 Tallinn, Estonia;

    Department of Earth Sciences,Natural History Museum, London SW7 5BD, UK;

    South Australian Museum, North Terrace, Adelaide, South Australia 5000, Australia,School of Earth and Environmental Sciences, The University of Adelaide, South Australia 5005, Australia;

    Research School of Earth Sciences, The Australian National University, Canberra, Australian Capital Territory 0200, Australia;

    Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, PO Box 643, Beijing 100044, China;

    Department of Organismal Biology, Evolutionary Biology Centre, Uppsala University, Norbyvaegen 18A, 752 36 Uppsala, Sweden;

    Vine Lodge, Vine Road, Johnston, Haverfordwest, Pembrokeshire SA62 3NZ, UK;

    6 Burghley Road,Wimbledon, London SW19 5BH, UK;

    University of Amsterdam, Science Park 904,1098XH, Amsterdam, The Netherlands;

    School of Biological Sciences, Flinders University, 2100, Adelaide, South Australia 5001, Australia;

    Western Australian Organic and Isotope Geochemistry Centre, Department of Chemistry, Curtin University, Perth, Western Australia 6102, Australia,Earth and Planetary Sciences, Western Australian Museum, Perth, Western Australia 6000, Australia;

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