Phylogenomic analyses of deep gastropod relationships reject Orthogastropoda

Abstract

Gastropods are a highly diverse clade of molluscs that includes many familiar animals, such as limpets, snails, slugs, and sea slugs. It is one of the most abundant groups of animals in the sea and the only molluscan lineage that has successfully colonised land. Yet the relationships among and within its constituent clades have remained in flux for over a century of morphological, anatomical and molecular study. Here we reevaluate gastropod phylogenetic relationships by collecting new transcriptome data for 40 species and analysing them in combination with publicly available genomes and transcriptomes. Our datasets include all five main gastropod clades: Patellogastropoda, Vetigastropoda, Neritimorpha, Caenogastropoda and Heterobranchia. We use two different methods to assign orthology, subsample each of these matrices into three increasingly dense subsets, and analyse all six of these supermatrices with two different models of molecular evolution. All twelve analyses yield the same unrooted network connecting the five major gastropod lineages. This reduces deep gastropod phylogeny to three alternative rooting hypotheses. These results reject the prevalent hypothesis of gastropod phylogeny, Orthogastropoda. Our dated tree is congruent with a possible endPermian recovery of some gastropod clades, namely Caenogastropoda and some Heterobranchia subclades.

Re-evaluating the phylogeny of Sipuncula through transcriptomics

“…1 and 2). Given our low levels of missing data and high matrix completeness (especially for the small matrix Taxon75: maximum of 23% of missing data for Phascolopsis gouldii), similar to other studies with comparable matrices and data analysis strategies (e.g., Andrade et al, 2014;Zapata et al, 2014), we think that our results should not be affected by gene occupancy or missing data artifacts. With the aim of having the most complete dataset possible, we optimized taxon sampling to represent all sipunculan families, ensuring that no major phylogenetic hypothesis was left untested for deep relationships within Sipuncula.…”

Neuromuscular development in Patellogastropoda (Mollusca: Gastropoda) and its importance for reconstructing ancestral gastropod bodyplan features

“…; Schrödl ; Zapata et al. ), it seems likely that the condition with two obliquely striated, shell attached larval retractor muscles as found in the basal branching clades such as Patellogastropoda and Vetigastropoda represents the ancestral condition for Gastropoda.…”

The origins of molluscs

“…Within this latter clade, the following topology is seen (Neritimorpha (Caenogastropoda + Heterobranchia)) (Zapata et al . ).…”