Phylogeny and character evolution in Grania (Annelida, Clitellata)

De Wit, P., Rota, E. & Erséus, C. (2011) Phylogeny and character evolution in Grania (Annelida, Clitellata). —Zoologica Scripta, 40, 509–519. In this study, DNA sequences from six loci of twenty species are combined with a 54‐character morphological matrix coded for all 72 described species of the marine clitellate genus Grania (Enchytraeidae) in the first ever attempt to illuminate the phylogeny of the group. The data are found to be inadequate for resolving the phylogeny of the entire genus, but a well‐supported, fully resolved phylogeny of the subset of twenty species for which DNA data are available is found through both Bayesian inference and maximum parsimony. Using well‐supported nodes from the Bayesian analysis, we investigate the morphological character evolution using parsimony ancestral state reconstruction. We find that most morphological characters used in standard species descriptions are homoplasious. Morphological characters that are found to be homological within clades (although not globally) include chaetal characters, midventral glands, penial stylets, coloration and possession of a head organ. Surprisingly, the head organ is strongly suggested as having evolved at least twice within the genus, but an alternative hypothesis is that this structure is an ancestral feature of the genus that has been secondarily lost, or simply has not been optically detected, in some lineages. Also, the geographical distributions of the Grania species used in the DNA analysis tend to follow the phylogeny, indicating limited dispersal capabilities.