Title

Evolutionary relationships among the major lineages of tapeworms (Platyhelminthes: Cestoidea) inferred from 18S ribosomal DNA and elongation factor 1-alpha sequence data

Date of Completion

January 1998

Keywords

Biology, Genetics|Biology, Zoology

Degree

Ph.D.

Abstract

Phylogenetic relationships among the 14 major lineages of tapeworms (Platyhelminthes: Cestoidea) were examined by analysis of 18S ribosomal DNA (rDNA) and Ef-1α gene sequences. Complete 18S rDNA gene sequences were determined from freshly collected specimens of 23 species of tapeworms representing 14 orders: Amphilinidea (Schizocoerus liguloideus); Caryophyllidea (Hunterella nodulosa); Cyclophyllidea (Hymenolepis diminuta); Diphyllidea (Echinobothrium fautleyae, Macrobothridium sp.); Gyrocotylidea (Gyrocotyle rugosa); Haplobothriidea ( Haplobothrium globuliforme); Lecanicephalidea (Cephalobothrium aetiobatidis, Eniochobothrium gracile); Nippotaeniidea ( Amurotaenia decidua); Proteocephalidea (Proteocephalus prolixus ); Pseudophyllidea (Diphyllobothrium stemmacephalum, Schistocephalus solidus); Spathebothriidea (Spathebothrium simplex); Tetrabothriidea (Tetrabothrius fosteri); Tetraphyllidea ( Anthobothrium laciniatum, Calliobothrium sp., Litobothrium alopias, Platybothrium auriculatum, Renyxa amplifica, Rhinebothrium maccallumi ); Trypanorhncha (Hepatoxylon sp., Tentacularia sp.). In addition, approximately 900 nucleotides of the Ef-1α gene were determined for all of the taxa above, except for E. fautleyae and G. rugosa. Maximum parsimony and minimum evolution (using both maximum likelihood-estimated, as well as log determinant-transformed genetic distances) analyses were performed on eight partitions of the sequence data. Different data partitions and different methods of analysis produced varied results, however, strongly supported nodes were generally recovered by all analyses. The 18S rDNA data support the basal position of the amphilinidean and gyrocotylidean taxa relative to the eucestode taxa, and both genes support the monophyly of the Eucestoda. Within the Eucestoda, the spathebothriidean was consistently shown to be the most basal taxon followed, generally, by the caryophyllidean taxon. The remaining orders generally formed a derived clade with the difossate orders being either basal or sister to a monophyletic clade consisting of the tetrafossate orders. Strongly supported relationships included a sister relationship between the haplobothriidean taxon and the pseudophyllidean taxa, a monophyletic clade consisting of the cyclophyllidean, nippotaeniidean and tetrabothriidean taxa, and the association of the proteocephalidean taxon with the tetraphyllidean taxa. ^