Andrea Barco

A molecular phylogenetic framework for the Muricidae, a diverse family of carnivorous gastropods.

With over 1600 extant described species, the Muricidae are one of the most species-rich and morphologically diverse families of molluscs. As predators of molluscs, polychaetes, anthozoans barnacles and other invertebrates, they form an important component of many benthic communities. Traditionally, the classification of muricids at specific and generic levels has been based primarily on shells, while subfamilies have been defined largely by radular morphology, although the composition and relationships of suprageneric groups have never been studied exhaustively. Here we present the phylogenetic relationships of 77 muricid species belonging to nine of the ten currently recognized subfamilies, based on Bayesian inference and Maximum Likelihood analyses of partial sequences of three mitochondrial (12S, 16S and COI) and one nuclear (28S) genes. The resulting topologies are discussed with respect to traditional subfamilial arrangements, and previous anatomical and molecular findings. We confirm monophyly of each of the subfamilies Ergalataxinae, Rapaninae, Coralliophilinae, Haustrinae, Ocenebrinae and Typhinae as previously defined, but earlier concepts of Muricinae, Trophoninae and Muricopsinae are shown to be polyphyletic. Based on our phylogenetic hypothesis, a new arrangement of these subfamilies is proposed.

Identification of North Sea molluscs with DNA barcoding

Sequence‐based specimen identification, known as DNA barcoding, is a common method complementing traditional morphology‐based taxonomic assignments. The fundamental resource in DNA barcoding is the availability of a taxonomically reliable sequence database to use as a reference for sequence comparisons. Here, we provide a reference library including 579 sequences of the mitochondrial cytochrome c oxidase subunit I for 113 North Sea mollusc species. We tested the efficacy of this library by simulating a sequence‐based specimen identification scenario using Best Match, Best Close Match (BCM) and All Species Barcode (ASB) criteria with three different threshold values. Each identification result was compared with our prior morphology‐based taxonomic assignments. Our simulation resulted in 87.7% congruent identifications (93.8% when excluding singletons). The highest number of congruent identifications was obtained with BCM and ASB and a 0.05 threshold. We also compared identifications with genetic clustering (Barcode Index Numbers, BINs) computed by the Barcode of Life Datasystem (BOLD). About 68% of our morphological identifications were congruent with BINs created by BOLD. Forty‐nine sequences were clustered in 16 discordant BINs, and these were divided in two classes: sequences from different species clustered in a single BIN and conspecific sequences divided in more BINs. Whereas former incongruences were probably caused by BOLD entries in need of a taxonomic update, the latter incongruences regarded taxa requiring further investigations. These include species with amphi‐Atlantic distribution, whose genetic structure should be evaluated over their entire range to produce a reliable sequence‐based identification system.

Cenozoic evolution of Muricidae (Mollusca, Neogastropoda) in the Southern Ocean, with the description of a new subfamily

Barco, A., Schiaparelli, S., Houart, R. & Oliverio, M. (2012). Cenozoic evolution of Muricidae (Mollusca, Neogastropoda) in the Southern Ocean, with the description of a new subfamily. —Zoologica Scripta, 41, 596–616.

Ecological barcoding of corallivory by second internal transcribed spacer sequences: hosts of coralliophiline gastropods detected by the cnidarian DNA in their stomach

The second internal transcribed spacer (ITS2) of the nuclear ribosomal RNA cluster (rDNA) is significantly smaller in the Cnidaria (120–260 bp) than in the rest of the Metazoa. ITS2 is one of the fastest evolving DNA regions among those commonly used in molecular systematics and has been proposed as a possible barcoding gene for Cnidaria to replace the currently problematic mitochondrial sequences used. We have reviewed the intraspecific and interspecific variation of ITS2 rRNA sequences in the Anthozoa. We have observed that the lower limits of the interspecific DNA divergence ranges very often overlap with intraspecific ranges, and identical sequences from individuals of different species are not rare. This finding can result in problems similar to those encountered with the mitochondrial COI, and we conclude that ITS2 does not prove significantly better than COI for standard taxonomic DNA barcoding in Anthozoa.

Testing the applicability of DNA barcoding for Mediterranean species of top-shells (Gastropoda, Trochidae, Gibbula s.l.)

Abstract We employed the COI sequences from specimens of top-shells to: (a) test the applicability of COI as a barcode marker for the trochid genus Gibbula s.l.; (b) provide a first taxonomically reliable data set of COI sequences useful for future studies; and (c) detect evidence of suspect intraspecific variability over a large geographical scale. We analysed a data set of 150 sequences from specimens morphologically ascribed to 17 putative species of Gibbula from the Mediterranean Sea and northeastern Atlantic, including the type species of 9 taxa traditionally considered as subgenera of Gibbula and representing over 50% of the roughly two dozen Mediterranean species, and also provided the DNA barcode for the endangered Maltese top-shell Gibbula nivosa. The analysis of the data set revealed that the COI is an effective barcode for the identification of the northeastern Atlantic top-shells, and also provides a tool to detect cryptic diversity.

A molecular phylogenetic framework for the subfamily Ocenebrinae (Gastropoda, Muricidae)

The Ocenebrinae is a subfamily of marine predatory gastropods known as oyster and mussel drills. Their current phylogenetic framework is traditionally based on shell and radular characters, but a consensus on relationships among genera is still lacking. We investigated the molecular phylogeny of Ocenebrinae using 50 species and DNA data from one nuclear (28S) and two mitochondrial (COI and 16S) genes, the largest data set so far assembled for this subfamily. We found support for the monophyly of the Ocenebrinae, and species were divided into four major lineages. Within groups, genera had similar geographic distributions, suggesting that except in a few cases, species diversification within clades occurred without range expansions. We discuss the phylogenetic distribution of a labral tooth and a sealed siphonal canal, two characteristic ocenebrine features. We also show that Ocinebrina species in the north‐eastern Pacific are not monophyletic with north‐eastern Atlantic and Mediterranean species, and that the Ocinebrina edwardsii species complex belongs to Ocenebra.

Cryptic diversity in a chirally variable land snail

Abstract Jaminia quadridens (Mollusca: Gastropoda: Heterobranchia: Pulmonata: Stylommatophora: Enidae) is a land snail living up to 2400 m above sea level on calcareous meadow slopes. It is widely distributed in Central and Southern Europe, with two subspecies currently recognised (J. quadridens quadridens and J. quadridens elongata). Like other Enidae, the genus Jaminia is sinistrally coiled, whilst the vast majority of gastropods are dextral. Chirality in snails is determined in the early embryonic stages by a single gene with maternal effect. Following the discovery of reversed (dextral) populations in Abruzzi, we investigated the genetic variability of Jaminia quadridens in central and southern Italy. In fact, reversal of chirality is often associated with extremely rapid speciation in snails (“single gene speciation”), as gene flow between opposite chiral morphs can be severely reduced by pre-copula isolation mechanisms. Phylogenetic analyses with different inference methods, haplotype analyses and species delimitation analyses were carried out on cytochtome oxydase subunit I (COI) sequences of 126 Jaminia specimens from central and southern Italy, Sardinia and Provence. Our results suggested a complex framework, with at least five lineages that may represent distinct species, in agreement with biogeographic patterns previously reported for other terrestrial taxa. Southern populations of an ancestral stock probably underwent allopatric speciation while surviving in glacial refugia during the Pleistocene. Colonization of central Italy may be recent, with evidences of current gene flow between populations of a single species, which includes reversed individuals. The appearance of chiral reversal was statistically associated with marginal demes but apparently not related to other biological, ecological or historical factors. As land snails are generally severely affected by habitat degradation, due to their ecological requirements, our results have important implications for conservation. J. quadridens in Italy may comprise a complex of distinct species, mostly with restricted ranges, which may suffer from environmental changes more than a single, widely distributed species would.