A polyvalent and universal tool for genomic studies in gastropod molluscs (Heterobranchia)

Abstract

Molluscs are the second most diverse animal phylum and heterobranch gastropods present ~ 44,000 species. These comprise fascinating creatures with huge morphological and ecological disparity. Such great diversity comes with even larger phylogenetic uncertainty and many taxa have been largely neglected in molecular assessments. Genomic tools have provided resolution to deep cladogenic events but generating large numbers of transcriptomes/genomes is expensive and usually requires fresh material. Here we leverage a target enrichment approach to design and synthesize a probe set based on available genomes and transcriptomes across Heterobranchia. Our probe set contains 57,606 70mer baits and targets a total of 2,259 ultra-conserved elements (UCEs). Post-sequencing capture efficiency was tested against 31 marine heterobranchs from major groups, including Acochlidia, Acteonoidea, Aplysiida, Cephalaspidea, Pleurobranchida, Pteropoda, Runcinida, Sacoglossa, and Umbraculida. The combined Trinity and Velvet assemblies recovered up to 2,211 UCEs in Tectipleura, up to 1,978 in Nudipleura, and up to 1,927 in Acteonoidea, the latter two being the most distantly related taxa to our core study group. Total alignment length was 525,599 bp and contained 52% informative sites and 21% missing data. Maximum-likelihood and Bayesian inference approaches recovered the monophyly of all orders tested as well as the larger clades Nudipleura, Panpulmonata, and Euopisthobranchia. The successful enrichment of diversely preserved material and DNA concentrations demonstrate the polyvalent nature of UCEs, and the universality of the probe set designed. We believe this probe set will enable multiple, interesting lines of research, that will benefit from an inexpensive and largely informative tool that will, additionally, benefit from the access to museum collections to gather genomic data.