Excavating the roots of the tree of life: revealing a billion year fossil record for the euglenids

挖掘生命之树的根部：揭示眼虫十亿年的化石记录

• 批准号: NE/R001324/1
• 负责人: Charles Wellman
• 金额: $ 32.36万
• 依托单位: University of Sheffield
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FR001324%2F1
• 关键词: Excavating; roots; tree; life; revealing

In establishing the theory of evolution Charles Darwin realized that life originated only once and over billions of years diversified, through evolution, into the bewildering diversity of life on Earth today. Since this monumental paradigm shift a major goal of biology has been to establish the 'true tree of life' in terms of evolutionary relationships of the different types of organism and timing of their divergence. The most problematic and least understood regions of the tree of life are its deep roots: the origin of life and its early diversification. This is because these events occurred billions of years ago in the deep past and: (i) the primary divergence into the three domains of life (bacteria, archaea, eukaryotes) involved a complicated combining of organisms in 'endosymbiotic events'; (ii) the organisms involved are unfamiliar because modern relatives, if any, have changed dramatically through time; (iii) the fossil record is poor in rocks from such ancient times; (iv) techniques such as molecular clock analyses become unreliable the further back in time one investigates.The euglenids are a bizarre group of single-celled organisms common on the planet today. They inhabit freshwater environments where they move through the water using a unique motion called 'peristaltic movement'. Intriguingly, they either feed by ingesting matter (like animals) or through harvesting the Sun's energy (like plants). It is believed that they can do the latter because they combined with a photosynthetic unicellular green algae during a 'secondary endosymbiotic event'. Euglenoids are familiar to many of us as they are routinely examined in elementary laboratory classes, to familiarise students with the basic features of single-celled eukaryotes and the fact that some display characteristics of both animals and plants. Euglenids are particularly fascinating because studies of their anatomy and genome suggest they are among the most primitive of the earliest eukaryote organisms (that is organisms that have a true cell and evolved through the combination of more basic organisms (bacteria and archaea) that lack a true cell). Unfortunately euglenids lack a recognisable fossil record so we know little regarding their origin and evolutionary history.In order to remedy this major problem we have trawled the literature and discovered a number of fossils that have euglenid-like characters. Our insight is that we have discovered a way of recognising whether a fossil does indeed represent a true euglenid. Modern euglenids have a unique cell wall structure, and by taking extremely thin sections of their cell walls (less that 1/10,000 mm in thickness) and examining them under a powerful Transmission Electron Microscope, it is possible to identify this unique structure. We have undertaken preliminary studies on potential fossil euglenids and demonstrated that we can observe such structure in the fossils and hence prove that they are indeed euglenids. Some of the euglenid-like fossils are a staggering 1 billion years old.Our proposal is to analyse potential euglenid fossils from throughout the geological column and, by demonstrating which possess the characteristic euglenid wall structure, provide a continuous fossil record for the euglenids. This will place euglenids as one of the few groups of early divergent eukaryotes with a deep fossil record (and the first of the SuperGroup Excavates). This is important because it will provide evidence for the timing and nature of the diversification of the earliest eukaryotes. It will also provide an important fossil calibration point for molecular biologists that undertake molecular clock studies. Furthermore, we are addressing a highly topical research area and our findings will fuel current controversies concerning whether the eukaryotes evolved in the ocean or in fresh water and how and when euglenids acquired their secondary endosymbiotic green alga.

在建立进化论时，查尔斯·达尔文意识到生命的起源只有一次，经过数十亿年的进化，形成了今天地球上令人眼花缭乱的各种各样的生命。自从这一巨大的范式转变以来，生物学的一个主要目标就是建立“真正的生命之树”，根据不同类型生物的进化关系和它们分化的时间。生命之树中最有问题和最不为人所知的领域是它的深层根源：生命的起源和早期的多样化。这是因为这些事件发生在数十亿年前的远古时代，并且：(i)生命的三个领域（细菌，古细菌，真核生物）的主要分化涉及“内共生事件”中生物体的复杂组合；（ii）所涉及的生物是不熟悉的，因为现代的亲戚，如果有的话，已经随着时间发生了巨大的变化；（iii）如此远古时期的岩石化石记录很少；（iv）随着时间的推移，分子钟分析等技术变得越来越不可靠。真核生物是当今地球上常见的一种奇怪的单细胞生物。它们生活在淡水环境中，通过一种叫做“蠕动运动”的独特运动在水中移动。有趣的是，它们要么通过摄取物质（像动物一样）要么通过收集太阳的能量（像植物一样）来获取食物。人们相信它们能做到后者，因为它们在“次级内共生事件”中与一种光合作用的单细胞绿藻结合在一起。类真核生物对我们许多人来说都很熟悉，因为它们在小学实验课上经常被检查，让学生熟悉单细胞真核生物的基本特征，以及一些真核生物同时具有动物和植物特征的事实。真核生物特别令人着迷，因为对它们的解剖和基因组的研究表明，它们是最原始的最早的真核生物（即具有真正细胞的生物，通过缺乏真正细胞的更基本的生物（细菌和古细菌）的结合而进化而来）。不幸的是，真glenids缺乏可识别的化石记录，因此我们对它们的起源和进化历史知之甚少。为了解决这一主要问题，我们查阅了文献，发现了许多具有类似菊科动物特征的化石。我们的见解是，我们已经发现了一种方法来识别化石是否确实代表了真正的真核生物。现代真glenids具有独特的细胞壁结构，通过取其细胞壁的极薄切片（厚度小于1/10,000 mm）并在强大的透射电子显微镜下检查它们，可以识别这种独特的结构。我们对潜在的真glenids化石进行了初步研究，并证明我们可以在化石中观察到这种结构，从而证明它们确实是真glenids。一些类似绿藻的化石已经有10亿年的历史了。我们的建议是通过分析整个地质柱中潜在的真glenid化石，并通过展示具有特征的真glenid壁结构，为真glenid提供一个连续的化石记录。这将使真核生物成为为数不多的具有深层化石记录的早期真核生物分化群体之一（也是超级群体发掘的第一个群体）。这很重要，因为它将为最早的真核生物多样化的时间和性质提供证据。它也将为从事分子钟研究的分子生物学家提供一个重要的化石校准点。此外，我们正在解决一个高度热门的研究领域，我们的发现将加剧当前关于真核生物是在海洋中进化还是在淡水中进化以及真核生物如何以及何时获得次生内共生绿藻的争论。

项目成果

Pellicle ultrastructure demonstrates that Moyeria is a fossil euglenid

薄膜超微结构表明 Moyeria 是眼虫化石

• DOI: 10.1080/01916122.2019.1625457
• 发表时间: 2019
• 期刊: Palynology
• 影响因子: 1.5
• 作者: Strother P

Reconstructing the paleoenvironment of an oxygenated Mesoproterozoic shoreline and its record of life

• DOI: 10.1130/b36634.1
• 发表时间: 2024-03-01
• 期刊: GEOLOGICAL SOCIETY OF AMERICA BULLETIN
• 影响因子: 4.9
• 作者: Slotznick，Sarah P.;Swanson-Hysell，Nicholas L.;Strother，Paul K.
• 通讯作者: Strother，Paul K.

Sporopollenin chemistry and its durability in the geological record: an integration of extant and fossil chemical data across the seed plants

• DOI: 10.1111/pala.12523
• 发表时间: 2021-01-31
• 期刊: PALAEONTOLOGY
• 影响因子: 2.6
• 作者: Jardine, Phillip E.;Hoorn, Carina;Dupont-Nivet, Guillaume
• 通讯作者: Dupont-Nivet, Guillaume

Ginkgo leaf cuticle chemistry across changing pCO2 regimes

改变 pCO2 状态下的银杏叶角质层化学

• DOI: 10.1007/s12542-019-00486-7
• 发表时间: 2019
• 期刊: PalZ
• 影响因子: 1.8
• 作者: Jardine P

Dying in the Sun: Direct evidence for elevated UV-B radiation at the end-Permian mass extinction.

• DOI: 10.1126/sciadv.abo6102
• 发表时间: 2023-01-06
• 期刊: Science advances
• 影响因子: 13.6