We investigated the effects of different doses (0, 2.5, 25 and 250 μg) of the neuropeptide arginine vasotocin (AVT) on the calling characteristics of the grey treefrog in a chorus in its natural habitat. AVT changed some call characteristics known to influence social behaviour in grey treefrogs. It increased call duration and number of pulses in a call, but not dominant frequency, call rate or pulse effort. Saline injections and handling did not produce significant changes in any of the call characteristics. In addition, individual animals injected with AVT only rarely produced call characteristics that were outside of the range found in the preinjection measurements, suggesting that AVT does not cause abnormal calling behaviour. Other researchers have demonstrated that longer calls with more pulses are produced by males when chorus densities increase, and females display a strong preference for longer calls with more pulses. This suggests that the changes induced by AVT injections may have functional consequences in social interactions. We previously demonstrated that AVT-injected males (25 μg AVT) displaced resident males from calling sites through changes in calling behaviour under natural field conditions. Our results indicate that changes in call duration and pulse number could contribute to the unmanipulated resident male's behaviour towards the AVT-injected intruder, perhaps because the calls are more attractive to females or because the calls are perceived as more aggressive. (C) 2000 The Association for the Study of Animal Behaviour.
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