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Fecal testosterone in bighorn sheep (Ovis canadensis): behavioural and endocrine correlates

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Abstract:

Noninvasive endocrine techniques allow repeated sampling of the same individual to study causes and consequences of variation in individual behaviour and physiology. In this study, radioimmunoassay was used to measure fecal testosterone and to assess the repeatability of the testosterone assay for bighorn rams (Ovis canadensis). Fecal samples were collected from marked males during the pre-rut and the rut over 2 years. Results were highly repeatable for samples of the same ram within a day (r = 0.93). Fecal testosterone peaked during the pre-rut (when social relationships are established) and then declined from the pre-rut to the rut. For both years of study, fecal testosterone was correlated with social rank (2001: r = 0.73, P < 0.0001; 2002: r = 0.54, P = 0.007) and age (2001: r = 0.65, P = 0.002; 2002: r = 0.53, P = 0.008) of individual rams. When age was accounted for, however, the relationship between social rank and testosterone was no longer significant. Aggressiveness (measured as hourly interaction rate) was weakly correlated with fecal testosterone (r = 0.44, P = 0.039). There was no association between aggressiveness and social rank (r = 0.13, P = 0.591). To our knowledge, this is the first report of an association between testosterone levels and individual social rank in wild ungulates.

De nouvelles techniques non-invasives permettent de faire des dosages répétés des concentrations hormonales sur les mêmes individus afin d'étudier les causes et les conséquences de la variation individuelle du comportement et de la physiologie. Nous avons dosé par radio-immuno-essais la testostérone fécale et vérifié la répétabilité des analyses dans des échantillons prélevés sur de mâles marqués du mouflon d'Amérique (Ovis canadensis) pendant 2 ans durant le pré-rut et le rut. Nos résultats indiquent une très forte répétabilité des mesures de testostérone faites sur des échantillons prélevés sur un même individu au cours d'une même journée (r = 0,93). Les concentrations de testostérone atteignent un maximum au cours du pré-rut (période durant laquelle les mouflons établissent leur rang social) suivi d'une diminution graduelle jusqu'au rut. Au cours des 2 années de notre étude, les concentrations de testostérone fécale étaient en corrélation positive avec le rang social (2001 : r = 0,73, P < 0,0001; 2002 : r = 0,54, P = 0,007) et l'âge (2001 : r = 0,65, P = 0,002; 2002 : r = 0,53, P = 0,008) des mouflons. Cependant, lorsque l'effet de l'âge est pris en compte, la corrélation entre le rang social et la testostérone disparaît. Il y a aussi une faible corrélation entre l'agressivité (mesurée par le nombre d'intéractions à l'heure : r = 0,44, P = 0,039) et la testostérone. Cependant, il n'y a aucune corrélation entre le rang social et l'agressivité (r = 0,13, P = 0,591). À notre connaissance, notre étude est la première à démontrer l'existence d'une relation entre le rang social et la concentration de testostérone chez les ongulés sauvages.

Document Type: Research Article

Publication date: October 1, 2003

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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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