On the phylogenetic relationships among tetraphyllidean, lecanicephalidean and diphyllidean tapeworm genera

摘要

This study had 2 main objectives: (1) to construct an extensive, explicit list of characters and character states that might serve as a starting point, and perhaps even a model, for the compilation of a more complete list of characters for all cestode taxa; and (2) to use this character list to generate a hypothesis of the phylogenetic relationships among species representing most of the tetraphyllidean, lecanicephalidean and diphyllidean genera. Specimens of one species in each of 48 genera of tetraphyllideans, 8 genera of lecanicephalideans, the 3 genera of diphyllideans, 2 genera of proteocephalideans and 2 genera of trypanorhynchs, were examined as whole-mounts and sections, with light and scanning electron microscopy. A list of 120 morphological characters was compiled. Four phylogenetic analyses were conducted using PAUP* and/or NONA. The first was a comprehensive analysis with the 56 tetraphyllidean and lecanicephalidean species as ingroups and the remaining 7 species as outgroups. The 2ndwas an analysis of the 3 diphyllidean species as ingroups and the 2 proteocephalidean and the 2 trypanorhynch species as outgroups. The 3rd was an analysis of the 8 lecanicephalidean species and the "tetraphyllideans" Echeneibothrium sp. and Pseudanthobothrium sp. nov. as ingroups and an outgroup consisting of the 7 species used as outgroups in the first analysis. In the 4th analysis, the ingroup consisted of the 14 hooked tetraphyllideans (onchobothriids), and the outgroup consisted of the 7 species used as outgroups in the first analysis. The results of these analyses support the following phylogenetic hypotheses. The diphyllideans are monophyletic and Echinobothrium sp. nov. and Macrobothridium sp. are more closely related to one another than either is to Ditrachybothridium macrocephalum. The tetraphyllideans, lecanicephalideans and proteocephalideans are more closely related to each other than they are to the diphyllideans or the trypanorhynchs. The ordinal status of the lecanicephalideans is dubious. The lecanicephalidean species are more closely related to some of the tetraphyllidean taxa than these tetraphyllidean taxa are to the remainder of the tetraphyllidean taxa. The proteocephalideans appear to belong within the tetraphyllidean clade. The "tetraphyllidean" species Echeneibothrium sp. and Pseudanthobothrium sp. nov. are members of the lecanicephalidean clade. The position of "Discobothrium" sp. nov. within the lecanicephalideans is dubious. Within the tetraphyllideans, the non-acetabulate species Litobothrium daileyi, Disculiceps galapagoensis and Cathetocephalus sp. are the most basal members of the group. The family Onchobothriidae is monophyletic, as it is currently defined. Within the onchobothriids, the uniloculate species are basal to the multiloculate species; the species with unipronged hooks are basal to the species with multipronged hooks. Although relationships among the phyllobothriids, as they are currently defined, remain poorly resolved, the family Phyllobothriidae is not monophyletic. These results suggest that some aspects of the classification of the lecanicephalidean and tetraphyllidean taxa require revision. However, such revision should be based on further analyses including a broader representation of the generaand species in these groups.