Turning a deaf ear: a test of the manipulating androgens hypothesis in house wrens Craig A. Barnett * , Sandrine G. Clairardin, Charles F. Thompson, Scott K. Sakaluk Behavior, Ecology, Evolution and Systematics Section, School of Biological Sciences, Illinois State University article info Article history: Received 26 March 2010 Initial acceptance 31 May 2010 Final acceptance 8 September 2010 Available online 27 October 2010 MS. number: A10-00214R Keywords: begging development manipulating androgens hypothesis parental care sexual conflict testosterone Troglodytes aedon The manipulating androgens hypothesis (MAH) proposes that female birds increase the level of testos- terone (T) in their eggs to promote greater offspring begging, and thereby elicit increased provisioning by their mates. We examined the effect of a positive in ovo manipulation of T on provisioning by house wren, Troglodytes aedon, parents, and concomitantly examined the begging response of nestlings. We also examined the mass of nestlings throughout their growth to assess the effect of T on their devel- opment, and three measures of nest performance: hatching success, nestling survival and the proportion of nestlings that fledged. Nestlings hatching from T-injected eggs begged more than nestlings hatching from control (oil-injected) eggs early in the nestling period, but not later in the nestling period. However, treatment had no effect on the levels of parental provisioning or nestling mass gain, nor any effect on hatching success or nestling survival. There was a significant increase in parental provisioning rate, but a decline in the size of prey taken to the nest over the course of the breeding season, which was likely the result of declining environmental quality. Our results support neither the MAH, nor the expectation that nestlings should grow at different rates in relation to in ovo titres of T. Ó 2010 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. The composition and quality of eggs in altricial bird species can vary both within and among clutches within the same species. For example, there are significant levels of variation in yolk androgens within clutches, among clutches and among populations of the same species in different geographical regions (Müller et al. 2007; Martin & Schwabl 2008). Most explanations for variation in yolk androgens focus on the differential allocation of testosterone (henceforth T) by females in eggs in response to environmental factors (Mousseau & Fox 1998a, b; Groothuis et al. 2005; Müller et al. 2007). Female manipulation of the levels of androgens in eggs might alter the developmental trajectory of embryos to better equip them to their environment (reviewed in: Groothuis et al. 2005; Navara & Mendonça 2008). Variation in levels of yolk androgens might also arise from differential sex allocation (Petrie et al. 2001; but see Gil et al. 2006; Loyau et al. 2007). Among the factors known to influence female allocation of androgens to their eggs are intrinsic factors such as body condition (Sandell et al. 2007; Safran et al. 2008), social status (Tanvez et al. 2008) and level of immune response (Gil et al. 2006). Extrinsic factors include social or breeding density (Groothuis & Schwabl 2002; Mazuc et al. 2003; Pilz & Smith 2004), mate quality (Gil et al. 1999; Michl et al. 2004; Loyau et al. 2007; Sandell et al. 2007) and food availability (Verboven et al. 2003). In recent years, considerable attention has focused on the effects of male quality and attractiveness on the allocation of androgens by females in eggs (reviewed in: Groothuis et al. 2005; Müller et al. 2007). However, the role that sexual conflict might play in androgen provisioning strategies of female birds has received less attention. Sexual conflicts between parents can arise because it is advan- tageous for individuals to coerce their mate to provide more care to the offspring than they otherwise would. In so doing, the coercer can invest less in the current reproductive event and thereby increase future reproductive value at the expense of its manipu- lated mate (Trivers 1972; Arnqvist & Rowe 2005; Houston et al. 2005). This fundamental conflict has favoured coercive tactics that function to increase levels of parental provisioning by an individual’s mate, as well as counteradaptations to nullify these tactics (reviewed in Arnqvist & Rowe 2005). Michl et al. (2004) suggested a candidate adaptation for coercion in birds: females might strategically adjust the level of androgens allocated to eggs to manipulate the level of paternal care. This is because elevated levels of T can increase the begging behaviour of nestlings (Schwabl 1996; Eising & Groothuis 2003; von Engelhardt et al. 2006; but see Pilz * Correspondence: C. A. Barnett, Behavior, Ecology, Evolution and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL 61790- 4120, U.S.A. E-mail address: optimalforager@hotmail.com (C.A. Barnett). Contents lists available at ScienceDirect Animal Behaviour journal homepage: www.elsevier.com/locate/anbehav 0003-3472/$38.00 Ó 2010 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.anbehav.2010.09.019 Animal Behaviour 81 (2011) 113e120