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Medical Forum / General / General / October 2005testosterone and increased parasite intensity
Proc Biol Sci. 2005 Nov 7;272(1578):2299-304. Interactions between intrinsic and extrinsic mechanisms in a cyclic species: testosterone increases parasite infection in red grouse. Seivwright LJ, Redpath SM, Mougeot F, Leckie F, Hudson PJ. Hill of Brathens Centre for Ecology and Hydrology Banchory, Aberdeenshire AB31 4BW, UK. Field studies of mechanisms involved in population regulation have tended to focus on the roles of either intrinsic or extrinsic factors, but these are rarely mutually exclusive and their interactions can be crucial in determining dynamics. Experiments on red grouse Lagopus lagopus scoticus have shown that population instability can be caused both by the effects of a parasitic nematode, Trichostrongylus tenuis, on host production or by changes in testosterone influencing aggressive behaviour and recruitment. We experimentally tested for an interaction between testosterone and T. tenuis in free-living male grouse. A total of 123 grouse were caught in autumn, treated with an anthelmintic to remove parasites, and then given either testosterone or empty, control, implants. After one month grouse were re-infected with a standard dose of parasites. We show that males with increased testosterone levels had greater parasite intensities than controls after one year. We discuss possible physiological and behavioural mechanisms linking testosterone and increased parasite intensity, and the implications for our understanding of complex, unstable population dynamics. "The Red Grouse ~ Field studies of mechanisms Involved in population regulation Have tended to focus On the roles of either intrinsic or extrinsic factors, But these are rarely mutually exclusive And their interactions can be crucial In determining dynamics. Experiments On red grouse Lagopus lagopus scoticus Have shown that population instability Can be caused both By the effects of a parachting blanc toad, Or a Saphic Ode recited ~ On the host's party plans, or the orchestral Production, either impacting Changes through the hours, Insciting or exciting aggressive behaviour And recruitment." ~ James & Michael & Howard, The 3 Wise Men "Long, mah ~ jongg, nightlong, Overlong, Ping ~ Pong, Prolong, prong, scuppernong, singsong, song, Souchong, strong, thong, throng, tong, undersong, Wong, ding ~ dong, knot at all Wrong." ~ Etude "Spine, spike, spire, spur ~ A pointed device secured In a rider's heel, to urge the horse onward, Prompting recognition, aptly rewarded For achievement ~ !" ~ Pearl "Blanc Toad goads to action, stimulated stimulus, Scintillated, something projects perfectly on par, Perks your ears, suggests a spur Sparkling surprise, A reminder ~ A projecting root or branch of The Knowledge Tree, A stiff sharp spine, as on Silver Wings or legs of a bird Or a Glittering Dragon ~ Fly, One hop on a cock's leg, a giddy gander gallivanting A gaff for a gamecock." ~ Laika "... and don't forget the rustlings And glowing eyes in the brush, or bush, riffling Under stars." ~ Dot "O, know ~ Never, Knot ~ !" ~ Folly "!Quoof!" ~ Callie, A pretty Capercaillie calling, cawing, >From riffled forest foliage "Golly, You're pretty ~ !" ~ Folly O, a lovely viola James plays, his bow, effortless, drifting on his barge ... O, a fine French Horn Michael blows, O, a fine keyboard tempo, Howard fingers, ebony, ivory, largo, if over ~ elegantly Articulated." ~ Golly |
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