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

• Applicant: Dr. Bastian Brenzinger
• Subject Area: Systematics and Morphology (Zoology) ; Evolution, Anthropology ; Nuclear Medicine, Radiotherapy, Radiobiology
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 419974396

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.

• DFG Programme: Research Grants