The rise of heterobranchs (Gastropoda) – comparative microanatomy and early evolution

遗传学和形态相结合的策略有可能随后重建生命的进化。异型腹足类(异型腹足纲)是两个最大的腹足纲之一，也是软体动物的一个分支。然而，起源和到目前为止最多样化、无处不在的真神经细胞的起源仍然不明。自20世纪80年代S以来，大约有十几个鲜为人知的科，大多是小体和海洋有壳蜗牛被确定为真神经纲和剩余的腹足纲之间的联系，包括类似多样性的后腹足纲。然而，由于目前综合研究的覆盖面不够，这些在系统发育上如此重要的所谓的低等异枝家族之间的关系仍然几乎没有解决，几乎没有比较解剖学或其他生物学数据来证实关于真神经门和异叉目的任何系统发育假说。在本项目中，我的目标是通过结合慕尼黑、哈佛和东京经验丰富的实验室的专业知识来解决这个问题，并使用基于高分辨率(组织学和CT)3D重建的详细显微解剖学研究，以及最先进的系统基因组学和基于Sanger测序的系统发育重建方法。我们目前的分类单元样本来自几年来的国际收集工作，已经涵盖了下异鳃藻科的所有物种和超过一半的属多样性。准备工作通常是对所有科的约100个样本的条形码基因COI进行首次测序，对涵盖大多数科的新转录本进行测序，并为12个未被研究且与本项目范围内的系统发育相关的科编制分类学专业知识、解剖学检查材料和部分3D重建。通过这项工作，我们有望在三年内完全解决异臂藻属的早期系统发育问题，并通过全面的可用于大规模比较解剖学的所有器官系统的显微解剖学数据来支持这一新的“异臂骨干树”。我们期望阐明异枝器官是如何在其进化的最初400年中如此剧烈地改变形态，从而利用下异臂类将这些有壳的分类群及其化石代表与Caenogastpoda和派生的真神经纲联系在一起，后者包括大多数生物学上更为人所知和生态上相关的海螺和柄眼陆生蜗牛。我们相信，我们的方法对于理解这两个物种丰富的类群中的生物学和进化具有很大的解释潜力，这些类群共同构成了近60%的软体动物多样性。

Combined strategies of genetics and morphology have the potential to subsequently reconstruct the evolution of life. Heterobranch gastropods (class Heterobranchia) are one of the two largest gastropod clades and by this also of Mollusca. However, the origin of derived and by far most diverse diverse, ubiquitous subclade Euthyneura is still obscure. Since the 1980's, about a dozen families of poorly known, mostly small-bodied and marine shelled snails have been identified as links between Euthyneura and the remaining Gastropoda including similarly diverse Caenogastropoda. However, due to a presently insufficient coverage by integrative studies, relationships of these phylogenetically so important so-called "lower" heterobranch families remain almost unsolved and little comparative anatomical or other biological data are available to substantiate any phylogenetic hypotheses on Euthyneura and Heterobranchia. In the present project, I aim to solve this problem by combining the expertise of highly experienced laboratories in Munich, Harvard, and Tokyo and to use detailed microanatomical studies based on high-resolution (histology and CT-based) 3D-reconstruction together with state-of-the-art phylogenomic and Sanger-sequencing-based phylogenetic reconstruction methods. Our present taxon sampling is derived from international collecting efforts spanning several years and already covers all of familial and over half the generic diversity of lower Heterobranchia. Preparative work was the often first-time sequencing of the barcoding gene COI for about 100 samples of all families, the sequencing of novel transcriptomes covering most families, and the compiling of taxonomic expertise, material for anatomical examination and partial 3D-reconstructions for 12 families identified as understudied and phylogenetically relevant for the scope of this project.By this we expect to fully solve early phylogeny of Heterobranchia within three years, and to support this new “heterobranch backbone tree” by comprehensive microanatomical data of all organ systems usable for large-scale comparative anatomy. We expect to shed light on how heterobranch organs so drastically changed morphology during the early 400 years of their evolution, thereby using lower Heterobranchia to link such shelled taxa and their fossil representatives to outgroup Caenogastropoda and derived Euthyneura, the latter including the majority of biologically much better-known and ecologically relevant seaslugs and stalk-eyed land snails. We believe our approach to have large explanatory potential for understanding biology and evolution in either of these species-rich groups, together forming almost 60% of mollusk diversity.