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Platyhelminth phylogenetics: a key to understanding parasitism?
Littlewood, D.T.J.; Cribb, T.H.; Olson, P.D.; Bray, R.A. (2001). Platyhelminth phylogenetics: a key to understanding parasitism?, in: Saló, E. et al. (Ed.) Proceedings of the 9th International Symposium on the Biology of the Turbellaria, Barcelona, Spain, June 2000 [CD-ROM]. Belgian Journal of Zoology, 131(Suppl. 1): pp. 35-46
In: Saló, E.; Watson, N.; Schockaert, E. (Ed.) (2001). Proceedings of the 9th International Symposium on the Biology of the Turbellaria, Barcelona, Spain, June 2000 [CD-ROM]. Belgian Journal of Zoology, 131(Suppl. 1). Koninklijke Belgische Vereniging voor Dierkunde = Société royale zoologique de Belgique: Diepenbeek. 1-236 pp., more
In: Belgian Journal of Zoology. Koninklijke Belgische Vereniging voor Dierkunde = Société royale zoologique de Belgique: Gent. ISSN 0777-6276, more
Peer reviewed article  

Also published as
  • Littlewood, D.T.J.; Cribb, T.H.; Olson, P.D.; Bray, R.A. (2001). Platyhelminth phylogenetics: a key to understanding parasitism? Belg. J. Zool. 131(Suppl. 1): 35-46, more

Available in Authors 
Document type: Conference paper

Keywords
    Evolution; Morphology; Morphology; Morphology; Origin; Parasitism; Phylogenetics; Tapeworms; Cestoda [WoRMS]; Digenea [WoRMS]; Eucestoda [WoRMS]; Monogenea [WoRMS]; Platyhelminthes [WoRMS]; Tricladida [WoRMS]; Turbellaria [WoRMS]; Marine

Authors  Top 
  • Littlewood, D.T.J.
  • Cribb, T.H., more
  • Olson, P.D.
  • Bray, R.A., more

Abstract
    The comparative method, the inference of biological processes from phylogenetic patterns, is founded on the reliability of the phylogenetic tree. In attempting to apply the comparative method to the understanding of the evolution of parasitism in the phylum Platyhelminthes, we have highlighted several points we consider to be of value along with many problems. We discuss four of these topics. Firstly, we view the group at a phylum level, in particular discussing the importance of establishing the sister taxon to the obligate parasite group, the Neodermata, for addressing such questions as the monophyly, parasitism or the endo or ectoparasitic nature of the early parasites. The variety of non-congruent phylogenetic trees presented so far, utilising either or both morphological and molecular data, gives rise to the suggestion that any evolutionary scenarios presented at this stage be treated as interesting hypotheses rather than well-supported theories. Our second point of discussion is the conflict between morphological and molecular estimates of monogenean evolution. The Monogenea presents several well-established morphological autapomorphies, such that morphology consistently estimates the group as monophyletic, whereas molecular sequence analyses indicate paraphyly, with different genes giving different topologies. We discuss the problem of reconciling gene and species trees. Thirdly, we use recent phylogenetic results on the tapeworms to interpret the evolution of strobilation, proglottization, segmentation and scolex structure. In relation to the latter, the results presented indicate that the higher cestodes are diphyletic, with one branch difossate and the other tetrafossate. Finally, we use a SSU rDNA phylogenetic tree of the Trematoda as a basis for the discussion of an aspect of the digenean life-cycle, namely the nature of the first intermediate host. Frequent episodes of host-switching, between gastropod and bivalve hosts or even into annelids, are indicated.

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