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

遗传学和形态学相结合的策略有可能随后重建生命的进化。异枝腹足纲（异枝纲）是软体动物中两个最大的腹足纲分支之一。然而，衍生的起源和到目前为止最多样化的多样化，普遍存在的亚支系Euthyneura仍然是模糊的。自20世纪80年代以来，大约有12个鲜为人知的家庭，大多数是小身体和海洋贝壳蜗牛，被确定为Euthyneura和剩余的腹足动物之间的联系，包括同样多样化的Caenogastropoda。然而，由于目前综合研究的覆盖范围不够，这些系统发育上如此重要的所谓“低”异支科的关系几乎没有得到解决，并且很少有比较解剖学或其他生物学数据可以证实任何关于Euthyneura和Heterobranchia的系统发育假设。在目前的项目中，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，并使用基于高分辨率（组织学和基于ct的）3d重建的详细微观解剖研究，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，来解决这个问题。我们目前的分类群抽样来自于多年来的国际收集工作，已经涵盖了所有的科系和一半以上的低等异支目的属系多样性。准备工作通常是首次对所有家族的约100个样本进行条形码基因COI测序，对覆盖大多数家族的新转录组进行测序，并对鉴定为研究不足的12个家族进行分类专业知识、解剖检查材料和部分3d重建，这些家庭与本项目的系统发育相关。通过这一研究，我们期望在三年内完全解决异支的早期系统发育问题，并通过所有器官系统的综合显微解剖数据来支持这一新的“异支骨干树”，这些数据可用于大规模的比较解剖学。我们希望揭示异枝器官在其进化的早期400年里是如何如此巨大地改变形态的，从而利用较低的异枝来将这些有壳的分类群及其化石代表与外类群Caenogastropoda和衍生的Euthyneura联系起来，后者包括大多数生物学上更知名的和生态相关的海蛞蝓和柄眼陆地蜗牛。我们相信，我们的方法对于理解这两个物种丰富的群体中的任何一个群体的生物学和进化都有很大的解释潜力，这些群体共同构成了近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.