A broadly resolved molecular phylogeny of New Zealand cheilostome bryozoans as a framework for hypotheses of morphological evolution

Larger and larger molecular phylogenies based on ever more genes are becoming commonplace with the advent of cheaper and more streamlined sequencing and bioinformatics pipelines. However, many groups of inconspicuous but no less evolutionarily or ecologically important marine invertebrates are still neglected in the quest for understanding species- and higher-level phylogenetic relationships using high-throughput sequencing approaches. Here, we alleviate this issue by presenting a 17 gene phylogeny of >200 newly sequenced cheilostome bryozoan species, mainly from New Zealand waters. New Zealand is our geographic region of choice as its cheilostome fauna is taxonomically, functionally and ecologically diverse, and better characterized than many other such faunas in the world. Using this most taxonomically broadly-sampled and statistically-supported cheilostome phylogeny to date, we tested several existing systematic hypotheses based solely on morphological observations. We find that lower taxonomic level hypotheses (species and genera) are very robust while our inferred trees often did not reflect current higher-level systematics (family and above), illustrating a general need for the rethinking of current hypotheses. To illustrate the utility of our new phylogeny, we reconstructed the evolutionary history of frontal shields (i.e. a calcified body-wall layer in ascus-bearing cheilostomes) and asked if the presence of a calcified frontal shield has any bearing on the diversification rates of cheilostomes.

随着测序成本降低、流程更精简的测序技术与生物信息学分析管线的普及，基于更多基因标记的大型分子系统发育研究正愈发常见。然而，在利用高通量测序技术探究物种及高级阶元系统发育关系的研究中，诸多看似不起眼却在演化与生态层面同样具有重要价值的海洋无脊椎动物类群仍未得到足够关注。本研究通过构建涵盖200余种新测序的、主要采自新西兰海域的唇口目苔藓动物（cheilostome bryozoan）物种的17基因系统发育树，填补了这一研究空白。我们选择新西兰作为研究区域，原因在于该区域的唇口目苔藓动物区系在分类学、功能与生态维度上均具有丰富多样性，且其物种特征的描述完善程度优于全球多数同类区系。依托当前分类采样覆盖最广、统计支持度最高的唇口目苔藓动物系统发育树，我们对数个仅基于形态学观察提出的现有分类系统假说进行了检验。研究结果显示，较低分类阶元（物种与属）的分类假说具有较高稳健性，而我们构建的系统发育树往往无法反映当前的高级阶元（科及以上）分类系统，这表明学界亟需重新审视现有分类假说。为阐明本研究构建的系统发育树的应用价值，我们对具囊孔唇口目苔藓动物的额盾（frontal shield，即承载囊孔的钙化体壁层）的演化历史进行了重建，并探讨了钙化额盾的存在是否对唇口目苔藓动物的多样化速率存在影响。