COMPARISON OF MOLECULAR AND PALEONTOLOGICAL DATA IN DIATOMS SUGGESTS A MAJOR GAP IN THE FOSSIL RECORD
COMPARISON OF MOLECULAR AND PALEONTOLOGICAL DATA IN DIATOMS SUGGESTS A MAJOR GAP IN THE FOSSIL RECORD
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DOI：
10.1046/j.1420-9101.1994.7020247.x
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发表时间：
1994-03-01
影响因子：
2.1
通讯作者：
ADOUTTE, A
中科院分区：
文献类型：
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作者：
PHILIPPE, H;SORHANNUS, U;ADOUTTE, A
硅藻是一种单细胞真核藻类，具有硅质骨架，具有广泛的化石记录和众多现存物种的罕见优势，从而提供了在原生生物群体中面对分子和古生物数据的机会。对5种硅藻28S核糖体RNA的一部分进行了测序，其发散时间是已知的。利用包括后生动物和后生动物在内的广泛数据库，估计了这些单细胞真核生物的核苷酸取代率，并与多细胞真核生物的核苷酸取代率进行了比较。当使用化石记录衍生的分化时间时，我们的结果表明硅藻的核苷酸取代率比脊索动物快5倍左右。但是，当使用相对速率测试时，可以观察到，在很长一段时间内，硅藻中的核苷酸取代率实际上可能比脊索动物稍慢。对于这种矛盾，提出了两种可能的解释：(i)相对速率测试的失败；（ii）前侏罗纪硅藻化石记录的空白。我们已经检查了我们关于相对速率测试的结果是有效的。因此，第二种假说，即侏罗纪以前的硅藻进化，实际上已经被一些非分子证据所证实。形态分化与遗传物种形成的解耦似乎也已经发生，这可能部分解释了对最近枝发生事件日期的低估。
Diatoms, unicellular eukaryotic algae with a siliceous skeleton, offer the rare advantage of displaying both an extensive fossil record and numerous extant species, thus providing the opportunity of confronting molecular and paleontological data in a protist group. A portion of the 28S ribosomal RNA was sequenced from 5 diatoms, the divergence times of which are well known. The nucleotide substitution rate was estimated in these unicellular eukaryotes and compared with the rate of multicellular eukaryotes, using a broad data base comprising metazoans and metaphytes. When using fossil record derived divergence times, our results show that the nucleotide substitution rate is about 5 times faster in diatoms than in chordates. But, when using the relative rate test, it is observed that, over a long time period, the nucleotide substitution rate may in fact have been slightly slower in diatoms than in chordates. For this contradiction, two possible explanations are proposed: (i) a failure of the relative rate test, (ii) a gap in the pre-Jurassic diatom fossil record. We have checked that our results concerning the relative rate test were valid. Thus, the second hypothesis, which implies pre-Jurassic diatom evolution, in fact already suggested by some non-molecular evidences, is favoured. Decoupling of morphological differentiation from genetic speciation also appears to have occurred and may account in part for the underestimation of the dates of recent cladogenesis events.