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.
