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Sex ratio variation in gastrointestinal nematodes of Svalbard reindeer; density dependence and implications for estimates of species composition

Published online by Cambridge University Press:  13 December 2004

A. STIEN ,
M. DALLIMER ,
R. J. IRVINE ,
O. HALVORSEN ,
R. LANGVATN ,
S. D. ALBON  and
J. F. DALLAS
A. STIEN
Affiliation:
Department of Biology, University of Tromsø, N-9037 Tromsø, Norway
M. DALLIMER
Affiliation:
NERC Molecular Genetics in Ecology Initiative, School of Biological Sciences, University of Aberdeen, Zoology Building, Tillydrone Avenue, Aberdeen AB24 2TZ, UK
R. J. IRVINE
Affiliation:
Centre for Ecology and Hydrology, Banchory Research Station, Glassel, Hill of Brathens, Banchory, Aberdeenshire, AB31 4BW, UK
O. HALVORSEN
Affiliation:
Zoological Museum, University of Oslo, Sarsgate. 1, N-0562 Oslo, Norway
R. LANGVATN
Affiliation:
University Courses in Svalbard (UNIS), Longyearbyen, N-9170, Norway Norwegian Institute for Nature Research (NINA), Tunasletta-2, Trondheim, N-7040, Norway
S. D. ALBON
Affiliation:
The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK
J. F. DALLAS
Affiliation:
NERC Molecular Genetics in Ecology Initiative, School of Biological Sciences, University of Aberdeen, Zoology Building, Tillydrone Avenue, Aberdeen AB24 2TZ, UK
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Abstract

Estimates of the intensity and abundance of species provide essential data for ecological, evolutionary and epidemiological studies of gastrointestinal nematode communities. These estimates are typically derived from the species composition of adult males when only males have readily scorable species-specific morphological traits. Such estimation assumes that all species in the community have the same adult sex ratio. We evaluated this assumption for the trichostrongyle nematodes Ostertagia gruehneri and Marshallagia marshalli in infracommunities in Svalbard reindeer by identifying to species adult females using a polymerase chain reaction assay. The proportion of males was found to be slightly higher in O. gruehneri than in M. marshalli. Evidence for seasonal variation and density dependence in the adult sex ratio was only found for O. gruehneri. Possible demographic mechanisms for such sex ratio variation are discussed, and stochastic models that generate density-dependent sex ratios proposed. Sex ratio variation caused substantial bias in some male-based estimates of intensity of infection, while substantial and consistent bias in estimates of abundances was only evident in late winter samples. Our results suggest that estimating sex ratios can be particularly important in individual host level studies of nematode species of low abundance.

Keywords

Rangifer tarandusparasitedemographic modelsMCMC methodsWinBUGS
Type
Research Article
Information
Parasitology , Volume 130 , Issue 1 , January 2005 , pp. 99 - 107
Copyright
© 2004 Cambridge University Press

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