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Host-based identification is not supported by morphometrics in natural populations of Gyrodactylus salaris and G. thymalli (Platyhelminthes, Monogenea)

Published online by Cambridge University Press:  16 August 2007

K. OLSTAD ,
A. P. SHINN ,
L. BACHMANN  and
T. A. BAKKE
K. OLSTAD*
Affiliation:
Natural History Museum, Department of Zoology, University of Oslo, P.O. Box 1172, NO-0318 Oslo, Norway
A. P. SHINN
Affiliation:
Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, UK
L. BACHMANN
Affiliation:
Natural History Museum, Department of Zoology, University of Oslo, P.O. Box 1172, NO-0318 Oslo, Norway
T. A. BAKKE
Affiliation:
Natural History Museum, Department of Zoology, University of Oslo, P.O. Box 1172, NO-0318 Oslo, Norway
*
*Corresponding author: Natural History Museum, Department of Zoology, University of Oslo, P.O. Box 1172, NO-0318 Oslo, Norway. Tel: +47 22 85 18 23. Fax: +47 22 85 18 37. E-mail: kjetil.olstad@nhm.uio.no
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Summary

Gyrodactylus salaris is a serious pest of wild pre-smolt Atlantic salmon (Salmo salar) in Norway. The closely related G. thymalli, originally described from grayling (Thymallus thymallus), is assumed harmless to both grayling and salmon. The 2 species are difficult to distinguish using traditional, morphometric methods or molecular approaches. The aim of this study was to explore whether there is a consistent pattern of morphometrical variation between G. salaris and G. thymalli and to analyse the morphometric variation in the context of ‘diagnostic realism’ (in natural populations). Specimens from the type-material for the 2 species are also included. In total, 27 point-to-point measurements from the opisthaptoral hard parts were used and analysed by digital image processing and uni- and multivariate morphometry. All populations most closely resembled its respective type material, as expected from host species, with the exception of G. thymalli from the Norwegian river Trysilelva. We, therefore, did not find clear support in the morphometrical variation among G. salaris and G. thymalli for an a priori species delineation based on host. The present study also indicates an urgent need for more detailed knowledge on the influence of environmental factors on the phenotype of gyrodactylid populations.

Keywords

morphologysystematicsAtlantic salmonSalmo salargraylingThymallus thymallus
Type
Research Article
Information
Parasitology , Volume 134 , Issue 14 , December 2007 , pp. 2041 - 2052
Copyright
Copyright © Cambridge University Press 2007

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