PEET - Bivalves Project: Venerinae
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Trainee: Isabella Kappner, Ph.D. Student, University of Illinois at Chicago and Field Museum of Natural History, 2000-2007.
The marine bivalve subfamily Venerinae is an economically important group, nevertheless, its taxonomy and classification has been controversial for a long time. The subfamily was often synonymized with the subfamily Chioninae as having morphologically similar shells. The aim of this study was to clarify phylogenetic relationships of this group from family- to species-level and to provide a first view of historical biogeographic patterns in the subfamily. A subfamily-level study of the Veneridae was carried out, based on DNA sequence data of three genes (16S, COI and H3). Morphological characters were subsequently evaluated by mapping them onto the resultant phylogenetic tree (Kappner & Bieler, 2006). In this study the placement of Venerinae within the family Veneridae and in relation to the morphologically similar subfamily Chioninae was analyzed using Bayesian and maximum parsimony analyses. The outcome revealed that the molecularly-defined subfamily Venerinae should include some former chionine taxa, but overall it is genetically distinct from Chioninae. The study also showed that, despite a high amount of homoplasy in the morphological characters, a specific subset of those characters can be used to distinguish between members of the two subfamilies. If a venus clam shows crenulations on the interior shell margin, and has separated siphons and an anterior lateral tooth, it is a member of Venerinae. If it has crenulations on the interior margin and fused siphons, and lacks the anterior lateral tooth, it is a member of Chioninae.
The high degree of homoplasy of morphological characters is almost certainly to blame for the taxonomic uncertainty in past studies of this group. Members of several species pairs that are morphologically very similar actually belong to different subfamilies according to molecular data and, because these groups are not basal, similar morphological characters apparently evolved in parallel. One of these species pairs was analyzed in detail. The aim of this study was to find morphological characters that could be used to distinguish the two species, despite the morphological similarity of their exterior shell. Geometric morphometric techniques as well as dissections of soft bodies were utilized to investigate morphological differences. Besides the already-mentioned morphological Venerinae-Chioninae discriminators (siphonal fusion, anterior lateral tooth), this study found subtle but unambiguous morphological differences in the region of the pallial sinus. Phylogenetic relationships within the Venerinae sensu stricto were also investigated at species level. Molecular sequence data of three genes were analyzed together with morphological characters and resulted in a new classification for the subfamily. The historical biogeography of Venerinae was studied using biogeographic and fossil data to investigate the possible origin of this radiation. A systematic revision of the name-bearing genus Venus was completed. All 18 Recent species were redescribed and information on distribution, synonymy, taxonomy, and newly generated anatomical data were compiled.
Bieler, R., I. Kappner, and P. M. Mikkelsen. 2004. Periglypta listeri (Gray, 1838) (Bivalvia: Veneridae) in the western Atlantic: taxonomy, anatomy, life habits, and distribution. Malacologia, 46(2): 427-458, Proceedings of the International Marine Bivalve Workshop 2002.
Kappner, I. 2007. Phylogenetic Systematics of the Marine Bivalve Subfamily Venerinae Rafinesque, 1815. Ph.D. Dissertation, University of Illinois at Chicago, xxxii + 514 pp.
Kappner, I. & R. Bieler. 2006. Phylogeny of venus clams (Bivalvia: Venerinae) as inferred from nuclear and mitochondrial gene sequences. Molecular Phylogenetics and Evolution, 40(2): 317-331.
Kappner, I. 2002. Effects of various fixation techniques on tissue of a marine bivalve, Mercenaria mercenaria Linné, 1758 (poster). American Malacological Society, Charleston, South Carolina, 5 August 2002, p. 56.
Kappner, I. 2003. Preliminary phylogeny of the Venerinae (Mollusca, Bivalvia). American Malacological Society, Special Session: PEET Meets Molluscan Taxonomy, University of Michigan, Ann Arbor, Michigan, 28 June 2003, p. 35.
Kappner, I. 2004. Phylogeny of the subfamily Venerinae (Bivalvia: Veneridae) as inferred from morphology and molecules. Unitas Malacologia, Perth, Western Australia, 16 July 2004, p. 76.
Kappner, I., and R. Bieler. 2004. Evidence for convergence of the bivalve subfamilies Venerinae and Chioninae (Bivalvia: Veneridae). PEET V — Spatial and Temporal Issues in Taxonomy, Fifth Biennial Conference, 20-23 September 2004. Kappner, I., and R. Bieler.
Kappner, I. 2004. Phylogeny of the nominal subfamily Venerinae (Bivalvia: Veneridae) as inferred from morphology and molecules. SICB (Society for Integrative and Comparative Biology), New Orleans, Louisiana, 8 January 2004, on-line.
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