Ediacaran constraints on early animal evolution

在埃迪卡拉纪时期（6.31 - 5.41亿年前），动物首次出现在化石记录中，但动物进化需要近5000万年才能真正起飞，动物生命的快速多样化被称为寒武纪大爆发（~540 Ma）。埃迪卡拉纪生物的生物学和生态学还没有得到很好的解决，因为它们的身体结构与今天的生命和化石记录中的其他地方都有根本的不同。因此，人们对埃迪卡拉纪期间竞争和繁殖的关键进化过程是如何运作的知之甚少，因此也不清楚这些因素在相对缓慢的动物进化开始中发挥了什么作用。该提案的总体目标是了解埃迪卡拉纪期间这些过程的相互作用以及它们如何影响早期动物进化。生态统计数据对于研究埃迪卡拉古生物学非常有价值，因为整个群落都被记录在化石记录中，为使用通常只适用于生命系统的技术打开了大门。这些埃迪卡拉纪生命的多重“快照”之所以存在，是因为成千上万的固定生物被杀死并保存在它们生活的地方。这种原地保存意味着化石在岩石表面的位置封装了它们的生活史：它们如何繁殖，相互作用以及与环境的相互作用。我之前的工作利用空间分析来重建埃迪卡拉纪中这些繁殖和竞争的关键进化过程是如何运作的，发现至少有一个物种主要是无性繁殖，产生克隆群体，物种之间的竞争相对罕见。在这个提议中，我将通过解决三个关键问题来研究埃迪卡拉克隆群落对早期动物进化的影响：1）埃迪卡拉的低竞争率是克隆群落占主导地位的结果吗？我将确定埃迪卡拉群落在多大程度上由克隆群体主导，以及这些克隆群体内部的相互联系是否会导致资源共享，减少竞争。克隆群体的竞争可能会减少，因为如果资源可以在一个群体内共享，那么个体与相邻克隆体竞争没有任何好处。2)埃迪卡拉纪生态系统与现代生态系统有本质的不同吗？埃迪卡拉群落的竞争水平相对较低，这与现代深海系统形成鲜明对比，在现代深海系统中，竞争无处不在，大多数物种被认为相互竞争。通过分析现代深海群落的精细尺度群落结构，并将这些细节与埃迪卡拉群落进行比较，我将确定埃迪卡拉群落与现代群落的不同之处，并确定这种差异是由于克隆群落的流行，还是仅仅是不同环境的结果。3)埃迪卡拉纪的进化速度从根本上来说是缓慢的吗？在建立了克隆群体的流行及其对竞争和社区结构的影响之后，我将把这些信息输入性状进化和遗传多样性的理论模型。通过比较埃迪卡拉群落和现代群落之间这些模型的差异，我将调查任何差异对进化速率的影响，以确定埃迪卡拉群落的进化速率是否因为广泛的克隆性而降低，从而限制了早期动物的进化。

Animals first appear in the fossil record during the Ediacaran time period (631-541 million years ago), but it takes almost 50 million years for animal evolution to really take off, with a rapid diversification of animal life known as the Cambrian Explosion (~540 Ma). The biology and ecology of Ediacaran organisms are not well resolved because their body-plans are fundamentally different to both life today and elsewhere in the fossil record. Consequently, little is known about how the key evolutionary processes of competition and reproduction operate during the Ediacaran, and so it is not clear what role these factors play in the relatively slow start to animal evolution. The overarching objective of this proposal is to understand the interplay of these processes during the Ediacaran and how they influenced early animal evolution. Ecological statistics are incredibly valuable for studying Ediacaran palaeontology because entire communities are captured in the fossil record, opening the door for the use of techniques normally only applied to living systems. These multiple "snap-shots" of Ediacaran life exist because thousands of immobile organisms were killed and preserved where they lived. This in-situ preservation means that the positions of the fossils on their rock surface encapsulate their life-history: how they reproduced, interacted with each other and with their environment. My previous work utilised spatial analyses to reconstruct how these key evolutionary processes of reproduction and competition operated in the Ediacaran, finding at least one species was dominantly asexual, producing colonies of clones, and that competition between species was relatively rare. In this proposal I will investigate the consequences of Ediacaran clonal colonies on early animal evolution by addressing three key questions: 1) Are low Ediacaran competition rates a consequence of the dominance of clonal colonies? I will establish the extent to which Ediacaran communities were dominated by colonies of clones, and whether the inter-connectedness within these clonal colonies could have led to resource sharing, reducing competition. Competition is likely reduced for clonal colonies because if resources can be shared within a colony, there is no benefit to individuals out-competing their neighbouring clone. 2) Are Ediacaran ecosystems fundamentally different to modern ones? The relatively low levels of competition in Ediacaran communities stands in stark contrast to modern deep-sea systems, where competition is pervasive, and most species are thought to compete with each other. By analysing the fine-scale community structure of modern deep-sea communities, and comparing these details to Ediacaran communities, I will establish how the Ediacaran was different to the modern, and work out whether such differences were due to the prevalence of clonal colonies, or merely the result of differing environments. 3) Are Ediacaran evolutionary rates fundamentally slow? Having established the prevalence of clonal colonies and their impact on competition and community structure, I will feed this information into theoretical models of trait evolution and genetic diversification. By comparing how these models differ between the Ediacaran and modern communities, I will investigate the repercussions of any differences on evolutionary rates to establish whether Ediacaran evolutionary rates were reduced because of widespread clonality, thus limiting early animal evolution.