title: Towards more physiological manipulations of hormones in field studies: comparing the release dynamics of three kinds of testosterone implants, silastic tubing, time-release pellets and beeswax.
abstract: Hormone manipulations are of increasing interest in the areas of physiological ecology and evolution, because hormones are mediators of complex phenotypic changes. Often, however, hormone manipulations in field settings follow the approaches that have been used in classical endocrinology, potentially using supra-physiological doses. To answer ecological and evolutionary questions, it may be important to manipulate hormones within their physiological range. We compare the release dynamics of three kinds of implants, silastic tubing, time-release pellets, and beeswax pellets, each containing 3mg of testosterone. These implants were placed into female Japanese quail, and plasma levels of testosterone measured over a period of 30 days. Testosterone in silastic tubing led to supraphysiological levels. Also, testosterone concentrations were highly variable between individuals. Time-release pellets led to levels of testosterone that were slightly supraphysiological during the first days. Over the period of 30 days, however, testosterone concentrations were more consistent. Beeswax implants led to a physiological increase in testosterone and a relatively constant release. The study demonstrated that hormone implants in 10mm silastic tubing led to a supraphysiological peak in female quail. Thus, the use of similar-sized or even larger silastic implants in males or in other smaller vertebrates needs careful assessment. Time-release pellets and beeswax implants provide a more controlled release and degrade within the body. Thus, it is not necessary to recapture the animal to remove the implant. We propose beeswax implants as an appropriate procedure to manipulate testosterone levels within the physiological range. Hence, such implants may be an effective alternative for field studies.
authors.affiliation: Department of Behavioral Neurobiology, Max Planck Institute for Ornithology, Eberhard-Gwinner-Straße, 82319 Seewiesen, Germany. Electronic address: rquispe@orn.mpg.de.
authors.forename: Rene
authors.initials: R
authors.lastname: Quispe
authors.affiliation: Department of Behavioral Neurobiology, Max Planck Institute for Ornithology, Eberhard-Gwinner-Straße, 82319 Seewiesen, Germany.
authors.forename: Monika
authors.initials: M
authors.lastname: Trappschuh
authors.affiliation: Department of Behavioral Neurobiology, Max Planck Institute for Ornithology, Eberhard-Gwinner-Straße, 82319 Seewiesen, Germany.
authors.forename: Manfred
authors.initials: M
authors.lastname: Gahr
authors.affiliation: Department of Behavioral Neurobiology, Max Planck Institute for Ornithology, Eberhard-Gwinner-Straße, 82319 Seewiesen, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Goymann
mesh_terms: D000818:Animals; D003370:Coturnix / Q000378:metabolism*; D003692:Delayed-Action Preparations / Q000493:pharmacokinetics*; D004343:Drug Implants; D005260:Female; D007440:Intubation / Q000295:instrumentation*; D008297:Male; D012826:Silicone Elastomers; D013607:Tablets; D013739:Testosterone / Q000008:administration & dosage* / Q000097:blood*; D014018:Tissue Distribution; D014885:Waxes
chemical_list: D003692:Delayed-Action Preparations; D004343:Drug Implants; D012826:Silicone Elastomers; D013607:Tablets; D014885:Waxes; C038228:beeswax; D013739:Testosterone
keywords: Free-living; Japanese quail; Physiological range; Release rate; Steroid hormones