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 colonized 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 re-evaluate 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 12 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 end-Permian recovery of some gastropod clades, namely Caenogastropoda and some Heterobranchia subclades.

Positive selection on panpulmonate mitogenomes provide new clues on adaptations to terrestrial life

“…In the same study, significant levels of positive selection (ω = 6 or 12) were detected at the radiation of bony vertebrates (Euteleostomi), approximately 400–500 Ma [55]. In our data, divergence times are lower than in the vertebrate study: Euthyneura and Panpulmonata probably diverged from their sister groups 250–350 Ma and 150–250 Ma ago, respectively; while panpulmonate clades with terrestrial taxa diverged more recently (Ellobioidea: 140–160 Ma; Stylommatophora: 100–150 Ma) [3, 5]. …”

A multilocus molecular phylogeny of Fasciolariidae (Neogastropoda: Buccinoidea)

“…Perhaps phylogenomic analyses will be able to recover this part of the Neogastropoda tree with high support, as is usually the case with deep nodes in mollusks (Kocot et al, 2011;Smith et al, 2011;Zapata et al, 2014;Goodheart et al, 2015). Vermeij and Snyder (2006) considered Fasciolariinae as derived from early peristerniines and that the two groups are part of a single clade Fasciolariinae; Snyder et al (2012) noted that the subfamilies are morphologically similar.…”

What is the molluscan osphradium? A reconsideration of homology

“…There are few anatomical features that can readily be compared directly between different classes of molluscs, so a potential uniquely molluscan sense organ should be of great interest to molluscan phylogeny. Inter-relationships among major molluscan clades remains contentious (Sigwart and Lindberg, 2015) and different data-and taxon sets produce well-resolved yet mutually contradictory topologies (Smith et al, 2011;Stöger et al, 2013;Zapata et al, 2014). Variable structures identified as 'osphradia' have been reported in six of the eight living classes of molluscs.…”