Behav Ecol Sociobiol (2006) 59: 549–560 DOI 10.1007/s00265-005-0080-1 ORIGINAL ARTICLE Diego Rubolini . Maria Romano . Roberta Martinelli . Barbara Leoni . Nicola Saino Effects of prenatal yolk androgens on armaments and ornaments of the ring-necked pheasant Received: 18 April 2005 / Revised: 15 August 2005 / Accepted: 1 September 2005 / Published online: 25 October 2005 # Springer-Verlag 2005 Abstract Mothers may profoundly affect offspring pheno- type and performance by adjusting egg components, in- cluding steroid hormones. We studied the effects of elevated prenatal testosterone (T) exposure in the ring-necked pheasant on the expression of a suite of male and female traits, including perinatal response to stress, immune response, growth, and secondary sexual traits. Prenatal T levels were increased by injecting the yolk of unincubated eggs with physiological doses of the hormone. Yolk T injection resulted in a reduced length of male tarsal spurs, a trait which positively predicts male success in intra- and intersexual selection and viability, whereas no direct effect on male wattle characteristics or plumage traits of either sex was observed. Female spur length was also negatively af- fected by T, but to a lesser extent than in males. In addition, the covariation between male secondary sexual traits, which are reliable quality indicators, differed between T and control males, suggesting that the manipulation may have altered the assessment of overall male quality by other males and females. In conclusion, the negative effects of elevated yolk T on spur length, a trait which positively predicts male fitness, coupled with the lack of effects on growth or other traits in both sexes, provided limited evidence for mothers being subjected to a trade-off between positive and negative consequences of yolk T deposition on offspring traits and suggest that directional selection for reduced yolk T levels may occur in the ring-necked pheasant. Keywords Maternal effects . Multiple ornaments . Phasianus colchicus . Secondary sexual traits . Sex-specific effects . Testosterone Introduction Variation in egg composition can have profound conse- quences on the phenotype of the offspring (Williams 1994; Mousseau and Fox 1998; Price 1998; Dufty et al. 2002; Gil 2003; Groothuis et al. 2005a). By adjusting egg quality, individual females may thus influence offspring perfor- mance, under the limitations imposed by extrinsic condi- tions and maternal physiological constraints (Mousseau and Fox 1998; Price 1998; Groothuis et al. 2005a). The expression of such maternal effects mediated by egg quality may depend on maternal conditions and maternal environ- ment or may be affected by complex interactions between maternal and offspring genes, and extrinsic factors (Dufty et al. 2002). Since maternal effects can enhance phenotypic variation, for example through epistatic effects, which have the potential to affect the rate and direction of evolutionary changes (Wade 1998; Wolf et al. 1998), they have become the focus of increasing research interest. Cleidoic eggs of birds are provisioned by the mother with quantitatively minor components, including sex hormones (Schwabl 1993; reviews in Gil 2003; Groothuis et al. 2005a). Sex hormones are likely candidates as mediators of early maternal effects because maternal hormonal profiles and hormone transfer to the eggs may vary according to contingent maternal state and environmental conditions (Dufty et al. 2002; reviews in Gil 2003; Groothuis et al. 2005a). In addition, variable concentrations of egg hor- mones can have marked effects on offspring phenotype, and these effects may depend on the offspring genetic makeup, as simply exemplified by sex-related variation in suscepti- bility to sex hormones (Adkins-Regan et al. 1995; Williams 1999; von Engelhardt et al. 2004; Rubolini et al. in press). In fact, in vertebrates, sex hormones are known to exert per- vasive effects on the development of several organs and apparati, including for example the brain, and variation in the Communicated by J. Graves D. Rubolini Dipartimento di Biologia Animale, Università degli Studi di Pavia, p.zza Botta 9, 27100 Pavia, Italy M. Romano . R. Martinelli . B. Leoni . N. Saino (*) Dipartimento di Biologia, Università degli Studi di Milano, via Celoria 26, 20133 Milan, Italy e-mail: nicola.saino@unimi.it