Classical conditioning increases reproductive success in Japanese quail, Coturnix japonica MICHAEL J. MAHOMETA & MICHAEL DOMJAN Department of Psychology, University of Texas at Austin (Received 7 August 2003; initial acceptance 28 October 2003; final acceptance 11 June 2004; published online 17 February 2005; MS. number: A9674R) We examined the adaptive significance of learning by determining whether classicalconditioning increases reproductive success. Male and female quail received conditioning trials in which a small light (conditioned stimulus or CS) signalled access to a copulation partner. After this learning experience, pairs of subjects received a single 2-min (experiment 1) or 5-min (experiment 2) copulation test during which both the female and the male, only the female, only the male, or neither bird received the conditioned stimulus signalling access to a copulation partner. Signalling the copulatory episode for both the female and the male significantly increased the percentage of fertilized eggs that were produced and increased the efficiency of the copulatory behaviours that occurred. Presenting the CS to just one or the other sexual partner had no effect. These findings demonstrate that classical conditioning can enhance reproductive success, but the effect requires that both the male and the female be able to anticipate a sexual encounter. Ó 2004 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. Learning has been demonstrated in a wide range of vertebratespeciesincluding numerous fish, birds and mammals.Given its prevalence in the animalkingdom, it is reasonable to assume that ‘learning is a phenotypic trait that has evolved’( Plotkin 1988, page 135;see also Rozin & Schull 1988). However, direct demonstrations of the adaptive significance of learning are rare in the literature.Charlseworth (1995,page 187),for example, noted that ‘there are still no convincing empirical data to support the general hypothesis that cognition and learn- ing processes specifically make a necessary contribution to any species’ survival and reproductive success’. The pres- ent study was conducted to document the contribution of a particular form of learning, classicalconditioning, to fertility and reproductive success in Japanese quail. Classicalconditioning is a common form of learning that involves behaviouraladjustments to an impending biologically significant event or unconditioned stimulus (US), such as being bitten by a predator. Predatory attack elicits strong unconditioned responses automatically or reflexively.These defensive responses provide some pro- tection for the prey. However, more effective defence might be possible if the prey could respond in anticipation of the predatory attack.Classicalconditioning involves such learning, namely learning to anticipate an uncondi- tioned stimulus based on an antecedentcue or condi- tioned stimulus (CS). Historically, research on classical conditioning has focused on the mechanisms involved in learning to associate a CS with an US. However, Pavlov (1927) himself hypothesized that classicalconditioning is of adaptive significance,stating that the conditioned response of an organism is ‘directed towards the preservation of its existence’(page 8).Functional rather than mechanistic perspectives on classical conditioning are also increasingly prominent in more recent theoreticaldiscussions(e.g. Hollis 1990, 1997;Fanselow 1997;Domjan et al. 2000; Timberlake 2001). Encouraged by these speculations, investigators have initiated empirical studies to determine how classical conditioning facilitates the interaction of an organism with an unconditioned stimulus. In an early study, Hollis (1984) conditioned male blue gourami, Trichogaster trichopterus, to anticipate a territorial intruder. During conditioning trials, a brief red light (the CS) was presented just before visual exposure to an intruder (the US). For a control group, the CS and US presentations were explicitly unpaired. Following train- ing, the barrier between the subjects and the intruder was removed,permitting direct aggressive interactions. Con- ditioned subjects that received this test encounter follow- ing exposure to the CS showed more vigorous defensive Correspondence: M. Domjan, Department of Psychology, University of Texas at Austin, 1 University Station A8000, Austin, TX 78712-0187, U.S.A. (email: domjan@psy.utexas.edu). 983 0003–3472/04/$30.00/0 Ó 2004 The Association for the Study of Animal Behaviour.Published by Elsevier Ltd. All rights reserved. ANIMAL BEHAVIOUR, 2005, 69, 983–989 doi:10.1016/j.anbehav.2004.06.023