893. EVOLUTIONARY CHANGE IN DIATOM MORPHOLOGY : AN EXAMPLE FROM NITZSCHIA FOSSILIS TO PSEUDOEUNOTIA DOLIOLUS

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  • 893. 珪藻殻の形態変異にもとづく進化系列 : Nitzschia fossilis から Pseudoeunotia doliolus への一例
  • 珪藻殻の形態変異にもとづく進化系列--Nitzschia fossilisからPseudoeunotia doliolusへの一例〔英文〕
  • ケイソウ カク ノ ケイタイ ヘンイ ニ モトズク シンカ ケイレツ Nitz

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Pseudoeunotia doliolus gradually developed its convex dorsal margin from the Nitzschia fossilis morphology during the course of time since 2.00 m.y. B. P. This development corresponds with the general trend of the diatom temperature (Td) curve observed in the same sedimentary sections. However, the development of the convex dorsal margin is considered to have likely been caused by a genetic character rather than the effect of surface water temperature decline, because this evolutionary process does not correspond strictly with the climatic deterioration during the Pleistocene. Our SEM examination of the diatom valves of P. doliolus and N. fossilis shows that they have the same valve structure except for the valve symmetry. It is concluded that P. doliolus evolved from N. fossilis at the beginning of the Pleistocene and that these two species persisted for a period of about one m.y. until the disappearance of the latter species at 0.6 m.y. B.P. Therefore, this evolutionary change occurred during a time interval of 106 or more years.

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