Regina L Cunha; Cristina Grande; Rafael Zardoya

“ The reconstructed tree failed to recover the monophyly of Neogastropoda, and two Littorinimorpha lineages (Tonnoidea and Calyptraeoidea) were recovered as the closest sister groups of two Neogastropoda lineages (Volutidae and Cancellariidae, respectively) , although with low statistical support. In contrast, more recently, a phylogenetic analysis combining both morphological, and molecular data (using the same genes as in [15] ) recovered Neogastropoda as monophyletic [ [5] stimulating the debate. ”

“ The addition of nuclear data is needed to further confirm these new phylogenetic hypotheses.
Despite their remarkable present diversity, neogastropods have been traditionally recognized as a natural group because they share several key morphological features [1] , [5] , [9] , [32] , [17] . For instance, a recent phylogeny of Caenogastropoda based on 55 taxa and 164 morphological characters (particularly of external anatomy and eusperm) recovered neogastropods as a monophyletic group with maximal support [ [5] . ”

“ Four Metropolis-coupled Markov chain Monte Carlo (MCMC) analyses were run for 1 million generations, and sampled every 100 generations. The mixed model option was used for the amino acid sequence data sets. For the analysis of nucleotide sequence data sets, all 13 protein-coding genes, ribosomal RNAs, and tRNAs were considered as three different partitions in the allnuc data set. A fourth partition of nuclear genes was considered in the combined data sets. ”

“ ML phylogram inferred from a single concatenated data set of deduced amino acid sequences of all 13 mitochondrial protein-coding genes (13-protein data set) . Species whose complete mt genome was sequenced in this study are presented in bold. Lottia digitalis (Patellogastropoda) was used as outgroup. Numbers in the nodes correspond to ML bootstrap proportions (above branches) and BI posterior probabilities (below branches) . Only values above 70% are represented. The inset shows a ML topology based on fragments of mt and nuclear data (adapted from Fig. two of Colgan et al., 2007) . ”

“ In any case, combining all mt genes into a single data set always rendered the most resolved trees, supporting the use of complete mt genome data for addressing caenogatropod phylogeny.
Evolution of mitochondrial gene order of Neogastropoda
Shared mt gene orders may be useful for phylogenetic inference particularly at higher taxonomic levels [52] . Gastropods exhibit an important degree of variation in mt gene organization compared with other animals [ [20] , [53] - [54] . ”

“ The successive bursts of cladogenesis in the evolutionary history of the group could be hampering successful recovery of phylogenetic relationships within the group. Given the relatively short internodes connecting main superfamilies of Neogastropoda and related caenogastropod lineages, it seems worthwhile gathering and analyzing larger sequence data sets in order to obtain more phylogenetic informative sites for trying to resolve the question at hand. ”

“ Nevertheless, the rapid radiation at the origin of Neogastropoda may not allow full resolution of this phylogeny based only on mt data, and in parallel more nuclear sequence data will also need to be incorporated into the phylogenetic analyses.
Background
Neogastropoda [1] , [2] , also known as Stenoglossa [ [3] , comprises a highly diverse group of predatory marine shelled gastropods with more than 16,000 living species [ [4] including e.g., cone snails (Conidae) , balers (Volutidae) , purple dye murex snails (Muricidae) , augers (Terebridae) , and whelks (Buccinidae) [ [5] . ”

“ It is also noteworthy that internal branches in the phylogenetic tree based on the 13-protein data set (Fig. 2) presented higher bootstrap support than the ones in the phylogenetic tree based on the allnuc data set (Fig. 3) . This result is in agreement with the preferential use of amino acids to reconstruct deep phylogenies because they (1) have a larger character-state space compare to nucleotides, (2) show a slower rate of evolution compare to silent substitutions, and (3) are less influenced by compositional bias [46] ”

“ Thais clavigera ( [NC_010090 NC_010090] [30] ) , and Rapana venosa ( [NC_011193 NC_011193] [31] ) , (4) Opisthobranchia: Aplysia californica ( [NC_005827 NC_005827] , [57] ) and Roboastra europaea ( [NC_004321 NC_004321] , [53] ) ; (5) Pulmonata: Albinaria coerulea ( [NC_001761 NC_001761] , [58] ) ”