Investigating the Bivalve Tree of Life – an exemplar-based approach combining molecular and novel morphological characters

Abstract

Abstract. To re-evaluate the relationships of the major bivalve lineages, we amassed detailed morpho-anatomical, ultrastructural and molecular sequence data for a targeted selection of exemplar bivalves spanning the phylogenetic diversity of the class. We included molecular data for 103 bivalve species (up to five markers) and also analysed a subset of taxa with four additional nuclear protein-encoding genes. Novel as well as historically employed morphological characters were explored, and we systematically disassembled widely used descriptors such as gill and stomach 'types'. Phylogenetic analyses, conducted using parsimony direct optimisation and probabilistic methods on static alignments (maximum likelihood and Bayesian inference) of the molecular data, both alone and in combination with morphological characters, offer a robust test of bivalve relationships. A calibrated phylogeny also provided insights into the tempo of bivalve evolution. Finally, an analysis of the informativeness of morphological characters showed that sperm ultrastructure characters are among the best morphological features to diagnose bivalve clades, followed by characters of the shell, including its microstructure. Our study found support for monophyly of most broadly recognised higher bivalve taxa, although support was not uniform for Protobranchia. However, monophyly of the bivalves with protobranchiate gills was the best-supported hypothesis with incremental morphological and/or molecular sequence data. Autobranchia,

Phylogeny and origins of chemosynthetic vesicomyid clams

“…2). This result agrees with Bieler et al (2014), who generated a bivalve tree-of-life from nine gene fragments and ten fossil calibration points. They estimated a late Cretaceous to Mid-Cenozoic (95% HPD) split between 'Calyptogena' magnifica (Pliocardiinae) and 'Kelliella' sp.…”

Curious bivalves: Systematic utility and unusual properties of anomalodesmatan mitochondrial genomes

“…Although it is tempting to consider the carnivorous 459 septibranchs as a single clade, the two morphologically and taxonomically distinct septibranch taxa 460 (Tropidomya and Euciroa) do not cluster together in our analysis, as has proved the case in previous 461 studies with different taxa (Bieler et al 2014;Harper et al 2006). 462 463…”

Commensal associations and benthic habitats shape macroevolution of the bivalve clade Galeommatoidea

“…In addition, a more comprehensive calibration scheme is needed to better assess the timing of galeommatoidean diversification and the establishment of reef habitats. Owing to the lack of reliable internal fossil calibrations, analyses with additional external calibrations [55] are needed. One, perhaps, surprising result of this study is that commensal lineages diversified more slowly than free-living ones.…”