Browsing by Author "Varney, Rebecca M."

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    Assessment of mitochondrial genomes for heterobranch gastropod phylogenetics
    (BMC, 2021) Varney, Rebecca M.; Brenzinger, Bastian; Malaquias, Manuel Antonio E.; Meyer, Christopher P.; Schroedl, Michael; Kocot, Kevin M.; University of Alabama Tuscaloosa; University of Bergen; Smithsonian Institution; Smithsonian National Museum of Natural History; University of Munich
    BackgroundHeterobranchia is a diverse clade of marine, freshwater, and terrestrial gastropod molluscs. It includes such disparate taxa as nudibranchs, sea hares, bubble snails, pulmonate land snails and slugs, and a number of (mostly small-bodied) poorly known snails and slugs collectively referred to as the "lower heterobranchs". Evolutionary relationships within Heterobranchia have been challenging to resolve and the group has been subject to frequent and significant taxonomic revision. Mitochondrial (mt) genomes can be a useful molecular marker for phylogenetics but, to date, sequences have been available for only a relatively small subset of Heterobranchia.ResultsTo assess the utility of mitochondrial genomes for resolving evolutionary relationships within this clade, eleven new mt genomes were sequenced including representatives of several groups of "lower heterobranchs". Maximum likelihood analyses of concatenated matrices of the thirteen protein coding genes found weak support for most higher-level relationships even after several taxa with extremely high rates of evolution were excluded. Bayesian inference with the CAT+GTR model resulted in a reconstruction that is much more consistent with the current understanding of heterobranch phylogeny. Notably, this analysis recovered Valvatoidea and Orbitestelloidea in a polytomy with a clade including all other heterobranchs, highlighting these taxa as important to understanding early heterobranch evolution. Also, dramatic gene rearrangements were detected within and between multiple clades. However, a single gene order is conserved across the majority of heterobranch clades.ConclusionsAnalysis of mitochondrial genomes in a Bayesian framework with the site heterogeneous CAT+GTR model resulted in a topology largely consistent with the current understanding of heterobranch phylogeny. However, mitochondrial genomes appear to be too variable to serve as good phylogenetic markers for robustly resolving a number of deeper splits within this clade.
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    Complete mitochondrial genomes of two scaphopod molluscs
    (Taylor & Francis, 2019) Kocot, Kevin M.; Wollesen, Tim; Varney, Rebecca M.; Schwartz, Megan L.; Steiner, Gerhard; Wanninger, Andreas; University of Alabama Tuscaloosa; European Molecular Biology Laboratory (EMBL); University of Washington; University of Washington Tacoma; University of Vienna
    Complete mitochondrial genomes were determined for two scaphopod molluscs: the dentaliid Antalis entalis and an unidentified Antarctic gadilid. Both genomes are complete except, in Gadilida sp. indet., a short stretch of nad5 was undetermined and trnR could not be annotated. Organization of the Gadilida sp. genome is nearly identical to that previously reported for the gadilid Siphonodentalium whereas trnK, nad5, trnD, nad4, and nad4l are transposed to the opposite strand in the previously published Graptacme genome relative to that of Antalis. Phylogenetic analysis of the 13 protein-coding and 2 rRNA genes recovered Scaphopoda, Gadilida, and Dentaliida monophyletic with maximal support.
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    The Iron-Responsive Genome of the Chiton Acanthopleura granulata
    (Oxford University Press, 2021) Varney, Rebecca M.; Speiser, Daniel, I; McDougall, Carmel; Degnan, Bernard M.; Kocot, Kevin M.; University of Alabama Tuscaloosa; University of South Carolina Columbia; Griffith University; University of Queensland
    Molluscs biomineralize structures that vary in composition, form, and function, prompting questions about the genetic mechanisms responsible for their production and the evolution of these mechanisms. Chitons (Mollusca, Polyplacophora) are a promising system for studies of biomineralization because they build a range of calcified structures including shell plates and spine- or scale-like sclerites. Chitons also harden the calcified teeth of their rasp-like radula with a coat of iron (as magnetite). Here we present the genome of the West Indian fuzzy chiton Acanthopleura granulata, the first from any aculiferan mollusc. The A. granulata genome contains homologs of many genes associated with biomineralization in conchiferan molluscs. We expected chitons to lack genes previously identified from pathways conchiferans use to make biominerals like calcite and nacre because chitons do not use these materials in their shells. Surprisingly, the A. granulata genome has homologs of many of these genes, suggesting that the ancestral mollusc may have had a more diverse biomineralization toolkit than expected. The A. granulata genome has features that may be specialized for iron biomineralization, including a higher proportion of genes regulated directly by iron than other molluscs. A. granulata also produces two isoforms of soma-like ferritin: one is regulated by iron and similar in sequence to the soma-like ferritins of other molluscs, and the other is constitutively translated and is not found in other molluscs. The A. granulata genome is a resource for future studies of molluscan evolution and biomineralization.