Rates, patterns and divergence times among the Bryozoa: integrating fossil, molecular and morphological data

海洋群落是复杂的，容易受到非生物和生物因素驱动的变化的影响。许多群落的特点是存在无处不在的动物群体，无论纬度、深度或生物地理位置如何。这些类群中很少有出色的化石记录，很容易根据现有的分类群和生物学进行解释。苔藓虫门就是这样一类表现出这些特征的动物，它具有进一步定义的群居性特征。苔藓虫，或苔藓动物，是主要在海洋环境中发现的殖民地无脊椎动物，尽管有一类仅限于淡水。大多数活着的物种都有可化石的碳酸钙矿化骨架，它们的化石记录表明，它们的进化史可以追溯到4.5亿年前。苔藓虫是许多现代海底群落的重要组成部分。它们通常是在岩石、贝壳和海藻等坚硬表面上的早期定居者。它们生长迅速，积极争夺太空和浮游食物资源。它们为其他动植物在群落演替过程中提供了立体的栖息地。它们复杂的骨骼可以进行详细的形态计量分析。与竞争对手相互作用的证据可能被冻结在化石记录中，有性繁殖的模式和时间经常保存在骨骼中。它们也是研究殖民地进化古生物学的模式生物。然而，许多关键问题和假说仍然没有得到回答和检验，因为不同苔藓虫群之间(跨越许多分类水平)之间的相互关系是不确定的。因此，迫切需要一个强有力的进化框架。我们将集中讨论环口类，这是一个普遍存在的关键苔藓虫类群，自约4.7亿年前首次出现以来，一直作为附生底栖生物的成员发挥着重要作用。环口动物的寿命与它们与其他苔藓动物竞争的能力较差，以及它们的形态进化速度相对较慢是不一致的。我们将使用多基因、分子系统的方法来研究该门之间进化和灭绝的速度和模式，解决三个长期存在争议的问题：(1)今天生存的环口动物的主要亚群是什么时候分化的？(2)苔藓虫的三个亚类是如何相互关联的？(3)环口动物缓慢的形态进化速度是否与缓慢的分子进化速度相匹配？我们将使用分子标记来解决苔藓虫之间的相互关系。系统发育将通过化石记录中公认的分歧事件进行校准，使用现代统计技术来确定分歧时间。我们将建立一个强大的框架，从古生物学、灭绝模式、发育生物学和生活史战略方面理解整个门的辐射。预期的结果将对我们理解苔藓动物的进化和系统学产生巨大的影响。这将有助于了解当今海洋生物多样性的主要组成部分。分子系统学对于增进对苔藓动物门的认识至关重要，并将使苔藓虫更好地被用作群落性的模式生物和海洋生物群落生态的指示器。我们的发现有望对有关进化模式和过程的几个更广泛的问题产生重大影响，即：(1)分子和形态进化速度与物种形成速度之间的关系；(2)不同支系之间在地质时间上持续竞争对进化速度的影响；(3)幼虫类型和生活史策略对进化速度的影响；(4)高分类水平的大规模灭绝强度；以及(5)水生无脊椎动物生物矿化骨骼的起源及其在淡水栖息地定居时可能发生的次生损失。

Marine communities are complex and are subject to changes driven by both abiotic and biotic factors. Many communities are characterized by the presence of ubiquitous animal groups, regardless of latitude, depth or biogeography. Few of these groups have excellent fossil records that are easily interpreted in the light of extant taxa and biology. One such group of animals that exhibits these characteristics is the phylum Bryozoa, which has the further defining feature of being colonial. Bryozoans, or moss-animals, are colonial invertebrates found predominantly in marine environments, although one group is restricted to freshwaters. Most of the >6000 living species have fossilizable mineralized skeletons of calcium carbonate and their fossil record indicates an evolutionary history stretching back over 450 million years. Bryozoans are important components of many modern sea-bed communities. They are often early settlers on hard surfaces such as rocks, shells and seaweeds. They grow rapidly and compete actively for space and planktonic food resources. They provide three-dimensional habitats for other animals and plants in the process of community succession. Their complex skeletons are amenable to detailed morphometric analysis. Evidence of interactions with competitors may be 'frozen' in the fossil record, and modes and timings of sexual reproduction are frequently preserved in the skeleton. They are also model organisms for studying the evolutionary palaeobiology of coloniality. However, many key questions and hypotheses remain unanswered and untestable because the interrelationships between different bryozoan groups (across many taxonomic levels) are uncertain. Thus, there is an acute need for a robust evolutionary framework. We will concentrate on cyclostomes, a ubiquitous and key bryozoan group, that have maintained an important role as members of the epibenthos since their first appearance some 470 million years ago. The longevity of cyclostomes is at odds with their poor ability to compete with other bryozoans, and their relatively slow rate of morphological evolution. We will use a multigene, molecular systematic approach to investigate rates and patterns of evolution and extinction among the phylum, addressing three questions that have long been contentious: (1) When did the major subgroups of cyclostomes that live today diverge? (2) How are the three classes of bryozoans interrelated? (3) Have slow morphological rates of evolution in cyclostomes been matched by slow molecular rates of evolution? We will resolve bryozoan interrelationships using molecular markers. The phylogenies will be calibrated with well-established divergence events from the fossil record using modern statistical techniques to date divergence times. We will establish a robust framework for understanding the radiation of the entire phylum in terms of palaeobiology, patterns of extinction, developmental biology and life history strategies. Anticipated results will have an immense impact on our understanding of bryozoan evolution and systematics. This will provide an understanding of key components of present day marine biodiversity. Molecular phylogenies are critical to advancing knowledge of the phylum and will allow bryozoans to be better used as model organisms of coloniality and as indicators of marine community ecology. Our findings promise to have a major bearing on several wider issues concerning evolutionary patterns and processes, namely: (1) the relationship between molecular and morphological rates of evolution and speciation rate; (2) the influence of sustained competition between clades over geological time on evolutionary rates; (3) the effect of larval type and life-history strategies on evolutionary rates; (4) mass extinction intensities at high taxonomic level; and (5) the origin of biomineralized skeletons in aquatic invertebrates and their possible secondary loss when colonizing freshwater habitats.