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Body size and segmentation patterns in free-living and parasitic polychaetes

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Taxa that include both free-living and parasitic lineages present opportunities to examine if and how the life-history traits of parasitic organisms have diverged from those of their free-living relatives. In a comparative analysis the body sizes and numbers of body segments of parasitic polychaetes of the family Oenonidae were compared with those of free-living polychaetes from closely related families. There was no difference in body length between oenonids and free-living polychaetes. However, the parasitic oenonids attain, on average, a much higher number of body segments than their free-living counterparts. The number of segments per unit body length is also much higher in oenonids than in related free-living polychaetes. This suggests that new segments are produced at a higher rate or for longer periods in oenonids than in free-living polychaetes, in which the proliferation of new segments slows down over time to allow for the segments to grow in size. Given that each segment can produce gametes late in the life of the worm, the proliferation of segments in oenonids may be an adaptation to their parasitic life-style.

Les taxons qui comptent des lignées libres et des lignées parasites permettent d'examiner si et comment les caractéristiques du cycle biologique des organismes parasites ont pu diverger de celles des formes libres qui leur sont apparentées. La taille du corps et le nombre de segments corporels de polychètes parasites de la famille des Oenonidae ont été compares à ceux de polychètes libres de familles très apparentées. Il n'y a pas de différence entre les polychètes libres et les Oenonidae quant à la taille du corps. Cependant, chez les Oenonidae parasites, les segments du corps sont beaucoup plus nombreux que chez les polychètes libres. Le nombre de segments par unité de longueur du corps est aussi bien supérieur chez les Oenonidae, ce qui indique que la segmentation se fait à un rythme plus rapide ou sur une plus longue période chez les Oenonidae que chez les polychètes libres chez lesquels la prolifération des segments ralentit avec le temps, permettant aux segments de croître. Comme chaque segment peut produire des gamètes jusque tard dans la vie de l'animal, la prolifération des segments chez les Oenonidae peut être une adaptation à leur mode de vie parasitaire.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: May 1, 2001

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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