Friday, May 2, 2014

Towards a Bivalve Tree of Life

An important paper entitled “Investigating the Bivalve Tree of Life – an exemplar-based approach combining molecular and novel morphological characters” was recently published this year in Invertebrate Systematics.  This paper led by Rüdiger Bieler and Paula M. Mikkelsen and their team of 18 collaborators represents a significant product of their Bivalvia project (BivAToL), which is part of the Assembling the Tree of Life program sponsored by the National Science Foundation.  This paper, which uses an exemplar-based approach to generate morphological and molecular data from specimens from the same population or even the same specimen goes a long way towards providing the necessary phylogenetic infrastructure (sensu Bieler et al., 2013 and my April 2013 blog posting) for those interested in using bivalves as model organisms in a wide range of evolutionary and ecological studies. 

The BivAToL team examined stomach morphology and other features of the alimentary tract, the morphology of gills and labial palps, shell microstructure, and sperm ultrastructure.  Molecular markers included two nuclear ribosomal genes (18S and 28S rRNA), one nuclear protein encoding gene (histone H3), one mitochondrial ribosomal gene (16S rRNA) and one mitochondrial protein-encoding gene (cytochrome c oxidase subunit I; COI).  Four additional nuclear protein-encoding genes were also generated for a subset of taxa.  This impressive assemblage of data was analyzed using a variety of methods including parsimony, maximum likelihood and Bayesian inference with molecular data alone and in combination with the morphological characters.   The results consistently recovered the monophyly of Autobranchia, Pteriomorphia, Heterochonchia, Palaeoheterodonta, Archiheterodonta, Euheterodonta, Anomalodesmata and a new clade Imparidentia (=Euheterodonta excluding Anomalodesmata).  The authors also discussed the origin and diversification times for each of the major clades and provided a classification scheme for the six major monophyletic groups of modern Bivalvia.  This important paper is certain to stimulate much more research on bivalve systematics and and other interesting evolutionary questions.

Literature Cited

Bieler, R., P. M. Mikkelsen, T. M. Collins, E. A. Glover, V. L. González, D. L. Graf, E. M. Harper, J. Healy, G. y. Kawauchi, P. P. Sharma, S. Staubach, E. E. Strong, J. D. Taylor, I. Tȅmkin, J. D. Zardus, S. Clark, A. Guzmán, E. McIntyre, P. Sharp, and G. Giribet.  Investigating the bivalve tree of life – an exemplar –based approach combining molecular and novel morphological characters.  Invertebrate Systematics 28:32-115.

Bieler, R., P. M. Mikkelsen, and G. Giribet.  2013.  Bivalvia-A discussion of known unknowns.  American Malacological Bulletin 31(1):123-133.