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Gender-specific dispersal distances of grizzly bears estimated by genetic analysis

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Abstract:

Natal dispersal is difficult to quantify, and long-distance events are often undetected, leading to biased estimates. Following offspring from their natal home range to their postdispersal adult breeding home range is challenging, and gathering sufficient data for large mammals with long generation times is particularly difficult. Here we measure average sex-specific dispersal distances in grizzly bears (Ursus arctos L., 1758) using individual-based genetic analysis. We genetically sampled and generated 15-locus microsatellite genotypes for 711 grizzly bears over a range of 100 000 km2 in southwestern Canada. Microsatellite markers are inherited in a Mendelian fashion, allowing us to use likelihood-based parentage analyses to estimate parent–offspring dyads. We used the distance between individually captured females of parent–offspring pairs (i.e., mother–daughter) to estimate female natal dispersal distances and found that, on average, females dispersed 14.3 km from the center of their natal home range. We used the distance between males of parent–offspring pairs (i.e., father–son) to estimate average male dispersal distances and found that males dispersed, on average, 41.9 km from their natal, or maternal, home range (mother–son dispersal distance). We used a simulation model to estimate the bias associated with measuring the father–son (male–male) distance as an estimate of the mother–son distance.

La dispersion à la naissance est difficile à évaluer quantitativement et certains événements qui ont lieu sur de grandes distances peuvent souvent passer inaperçus, ce qui fausse les estimations. Suivre les petits depuis leur aire de naissance jusqu'à leur aire de reproduction à l'âge adulte après la dispersion présente un important défi, particulièrement chez les grands mammifères à durée de génération longue chez qui l'accumulation suffisante de données est particulièrement difficile. Nous avons mesuré la distance moyenne de la dispersion en fonction du sexe chez des grizzlis (Ursus arctos L., 1758) à l'aide d'une analyse génétique individuelle. Notre échantillonnage génétique a révélé l'existence de 15 génotypes reliés aux locus microsatellites chez 711 grizzlis sur un territoire de 100 000 km2 dans le sud-ouest du Canada. La transmission des marqueurs microsatellites suit un pattern de type mendéléen, ce qui nous permet de faire des analyses d'ascendance vraisemblable pour estimer les couples parent–petit. La distance entre les couples parent–rejeton (mère–fille) de femelles capturées individuellement a servi à estimer la distance de dispersion natale des femelles, soit en moyenne 14,3 km du centre de leur aire natale. La distance entre les couples parent–rejeton (père–fils) de mâles a servi à estimer la distance de dispersion natale des mâles, soit en moyenne 41,9 km du centre de leur aire natale ou de l'aire maternelle (distance de dispersion mère–fils). Un modèle de simulation a permis d'estimer l'erreur associée à la mesure de la distance père–fils (mâle–mâle) comme estimation de la distance mère–fils.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2004-07-01

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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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