With over 300 described species, the
chromodorid nudibranchs are one of the most species rich families of
gastropods. Their bright colors and
interesting morphology appeal to underwater photographers and scientists
alike. Their aposematic coloration has
also drawn the attention of scientists interested in natural products
chemistry. In spite of their
conspicuousness and appeal, there has been no comprehensive, well-supported
phylogeny of the chromodorid nudibranchs.
This hinders progress being made in other biological disciplines where
one may assume that species from the same genus represent a monophyletic
group. In a recent issue of PlosOne, Rebecca Johnson and Terrence
Gosliner set out to remedy this situation and generate a phylogeny of the
chromodorid nudibranchs and present a classification that accurately reflects
the evolutionary history of the group.
In the paper entitled “Traditional
Taxonomic Groupings Mask Evolutionary History: A Molecular Phylogeny and New
Classification of the Chromodorid Nudibranchs,” Johnson and Gosliner
assembled the most comprehensive dataset to date including 244 specimens (142
new), representing 157 species (106 new) chromodorid species and several other
taxa. They used two mitochondrial genes
(16S rRNA and cytochrome oxidase I) to reconstruct a phylogeny of the group. The results revealed that currently
recognized genera were either polyphyletic or nested within another genus
rendering the other genus paraphyletic.
Extensive homoplasy of morphological attributes that have been thought
to be synapomorphies for a particular genus seems to be the cause of the
unnatural groupings that have been recognized in the past. This pattern of polyphyly of recognized
genera has been observed for unionid bivalves as well (Campbell et al.,
2004).
One appealing outcome of the study by Johnson
and Gosliner (2012) is that they took the time to propose a new classification
of the group based on their findings. As
Johnson and Gosliner (2012) indicate, “the translation of phylogenetic
hypotheses into classifications is the best way to communicate results to a
larger community” and “communicating these new hypotheses is one of the main contributions
systematics can make to the scientific community.” Their study now provides a sound phylogenetic
framework from which morphological, chemical and behavioral attributes can be
examined.
Literature
Cited
Cambpell, D.
C., J. M. Serb, J. E. Buhay, K J. Roe, R. L. Minton, and C. Lydeard. 2005.
Phylogeny of North American amblemines (Bivalvia, Unonoida): prodigious
polyphyly proves pervasive across genera.
Invertebrate Biology 124:131-164.
Johnson, R.
F., and T. M. Gosliner. 2012. Traditional taxonomic groupings mask
evolutionary history: a molecular phylogeny and new classification of the
chromodorid nudibranchs. PlosOne 7(4):e33479.
