Most Cephalaspidea have a shell, but transcriptomes can provide them with a backbone (Gastropoda: Heterobranchia)

Vanessa L Knutson; Bastian Brenzinger; Michael Schrödl; Nerida G Wilson; Gonzalo Giribet

doi:10.1016/j.ympev.2020.106943

Most Cephalaspidea have a shell, but transcriptomes can provide them with a backbone (Gastropoda: Heterobranchia)

Mol Phylogenet Evol. 2020 Dec:153:106943. doi: 10.1016/j.ympev.2020.106943. Epub 2020 Aug 27.

Authors

Vanessa L Knutson¹, Bastian Brenzinger², Michael Schrödl³, Nerida G Wilson⁴, Gonzalo Giribet⁵

Affiliations

¹ Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford St, Cambridge, MA 02138, USA. Electronic address: vknutson@g.harvard.edu.
² SNSB - Zoologische Staatssammlung München, Münchhausenstr. 21, D-81247 Munich, Germany.
³ SNSB - Zoologische Staatssammlung München, Münchhausenstr. 21, D-81247 Munich, Germany; Department Biology II, Ludwig-Maximilians-Universität, 82152 Planegg-Martinsried, Munich, Germany; GeoBio-Center LMU, München 80333, Germany.
⁴ Collections & Research, Western Australian Museum, 49 Kew St, Welshpool 6106, WA, Australia; University of Western Australia, 35 Stirling Highway, Crawley 6009, WA, Australia.
⁵ Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford St, Cambridge, MA 02138, USA.

PMID: 32860975
DOI: 10.1016/j.ympev.2020.106943

Abstract

Cephalaspidea is an order of marine gastropods found worldwide, often in sandy or muddy habitats, which has a convoluted taxonomic history based on convergent or ill-defined morphological characters. The cephalaspidean shell-which can be external and robust, internal, or altogether absent in the adult-is of particular interest in this group, and a well-resolved phylogeny can give us greater insight into the evolution of this character. Molecular data have clarified many relationships within Cephalaspidea, but studies involving few Sanger sequenced phylogenetic markers remain limited in the resolution they provide. Here we take a phylogenomic approach, the first to address internal cephalaspidean relationships, sequencing and assembling transcriptomes de novo from 22 ingroup taxa-representing the five currently accepted superfamilies, 10 of the 21 currently recognized families, and 21 genera-and analyzing these along with publicly available data. We generated two main datasets varying by a minimum taxon occupancy threshold (50% and 75%), and analyzed these using maximum likelihood, Bayesian inference and a coalescence-based method. We find a consistent, well-supported topology, with full support across most nodes including at the family and genus level, which also appears to be robust to the effect of compositional heterogeneity among amino acids in the dataset. Our analyses find Newnesioidea as the sister group to the rest of Cephalaspidea. Within the rest of the order, Philinoidea is the sister group to a clade that comprises (Bulloidea (Haminoeoidea, Cylichnoidea)). There is strong support for several previously suggested, but tenuously supported relationships such as the genus Odontoglaja nesting within the family Aglajidae, and a sister group relationship between Gastropteridae and Colpodaspididae, with Philinoglossidae as their sister group. We discuss these results and their implications in the context of current cephalaspidean taxonomy and evolution. Genomic-scale data give a backbone to this group of snails and slugs, and hold promise for a completely resolved Cephalaspidea.

Keywords: Bubble snail; Molecular systematics; Phylogenomics; Phylogeny; Sea slug.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Animal Shells
Animals
Bayes Theorem
Gastropoda / anatomy & histology
Gastropoda / classification*
Gastropoda / genetics
Genome / genetics
Phylogeny*
Transcriptome*