Phylogeny of the Euhirudinea: Independent evolution of blood feeding by leeches?

Abstract

The phylogenetic relationships of leeches were investigated by examining 22 species representative of the 10 euhirudinean familes in a cladistic analysis. Forty-five characters relating to internal and external morphology as well as cocoon deposition characteristics were used. Polarization of character states was accomplished using Acanthobdella peledina as the sister-taxon to the Euhirudinea. Two equally parsimonious solutions resulted. One was chosen as a preferred tree on the basis of defensible character state transformations. Previous speculations as to evolutionary branching patterns are largely consistent with the results obtained by cladistic analysis. Similarly, contemporary taxonomic groupings of leeches into higher taxonomic categories were found to be largely consistent with monophyletic groups identified in the analysis. The family Piscicolidae was found to be paraphyletic; elevating the constituent piscicolid subfamilies to the level of family is proposed. The origin of sanguivory as a life-history mode was investigated by optimizing this characteristic on the phylogenetic hypothesis, indicating the possibility of at least two origins of blood-feeding in the evolutionary history of leeches, depending largely on how the feeding biology of acanthobdellids is interpreted. Sanguivory is seen to have been lost at least twice.