Enhanced yolk testosterone influences behavioral phenotype independent of sex in Japanese quail chicks Coturnix japonica Jonathan Niall Daisley a, * , Vivien Bromundt a , Erich Mfstl b , Kurt Kotrschal a a Konrad Lorenz Forschungsstelle, Gru ¨nau im Almtal 11, A-4645, Austria b University of Veterinary Sciences, J-Baumann Gasse 1, A-1210 Vienna, Austria Received 26 July 2002; revised 25 May 2004; accepted 30 September 2004 Available online 15 December 2004 Abstract Studies have demonstrated an effect of yolk testosterone levels on the physiology and behavior of nestling birds. In order to investigate this phenomenon experimentally in a precocial bird, we enhanced yolk testosterone, but within the physiological range, by injecting 50 ng testosterone in ethanol into Japanese quail Coturnix japonica eggs prior to incubation. The chicks hatching from these as well as from control eggs that had received the carrier-only or were left unmanipulated were subject to a number of behavioral tests from hatching to the age of 3 weeks. In addition, fecal samples were taken during a 90-min isolation period to determine a physiological response to a stressor. Experimental chicks performed a detour task faster and approached novel objects sooner than did the controls. Chicks from treated eggs took a longer time to start distress vocalizing and also produced less distress calls during open-field trials, took on average a larger number of trials for them to show tonic immobility and also excreted lower levels of corticosterone metabolites (BM) than did the controls. In response to a stressor, excreted BM was initially higher in the control chicks, as compared to the experimental birds. Induced behavioral effects were independent of sex with no sex treatment interactions found. In sum, experimentally enhanced testosterone levels in the eggs shifted individual behavioral phenotype towards bboldQ or bproactiveQ, irrespective of sex. We conclude that testosterone in the yolk influences the coping style of hatchlings and may be a potential means of maternal influence on offspring phenotype. D 2004 Elsevier Inc. All rights reserved. Keywords: Quail; Coturnix; Steroid; Egg yolk; Epigenetics; Coping style Phenotypic characters are based on genetic inheritance. In addition, certain epigenetic factors may come into play. Most notably, parental effects may influence offspring phenotype. In birds, for example, females may increase their level of care (De Lope and Moller, 1993), lay more eggs (Petrie and Williams, 1993) or lay larger eggs (Cunningham and Russell, 2000). In addition, it has been shown that egg yolk contains high concentrations of steroids and that the amount deposited may be under maternal influence (Burley and Vadehra, 1989; Schwabl, 1993). Recent evidence suggests that the amount of steroid deposited in the egg yolk may be influenced by the female’s social and physical environments (see Eising et al., 2001; Schwabl, 1996a,b). In this way, yolk steroid levels are influenced by breeding density (Schwabl, 1997), male attractiveness (Gil et al., 1999), social intrusion (Mazuc et al., 2003) and/or female condition (Verboven et al., 2003). These differences in steroid levels may result in epigeneti- cally derived phenotype variation within a clutch, since steroids have strong organizational effects on the developing embryonic nervous system (Sapolsky, 1992) and have morphological, physiological and behavioral effects on offspring traits (Eising, 2004; Ketterson and Nolan, 1999; Ros, 1999). Most studies have focused on the effects of maternally derived testosterone in the eggs of asynchronously hatch- 0018-506X/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.yhbeh.2004.09.006 * Corresponding author. School of Biology, University of Nottingham, Nottingham NG7 2RD, UK. Fax: +44 115 9513251. E-mail address: jndaisley@msn.com (J.N. Daisley). Hormones and Behavior 47 (2005) 185 – 194 www.elsevier.com/locate/yhbeh