Authors: Michael S Reichert
Publish Date: 2009/10/17
Volume: 64, Issue: 4, Pages: 529-539
Abstract
Males in many chorusing anuran species use aggressive calls during defense of calling spaces from other males The minimal intensity of another male’s vocalizations that elicits an aggressive call response has been termed the aggressive threshold Previous studies of aggressive thresholds have shown that they are plastic males habituated increased their aggressive thresholds in response to repeated presentation of stimuli above initial threshold levels Habituation likely contributes to the stable chorus structure of these species in which aggressive calling is rare compared to advertisement calls I have observed high levels of aggressive calling in the treefrog Dendropsophus ebraccatus suggesting that males of this species do not habituate In this study I investigated the plasticity of aggressive thresholds in D ebraccatus I measured the aggressive thresholds of males before and after suprathreshold stimulation by both advertisement and aggressive calls I found that the different call types had different effects males habituated to advertisement calls but lowered their aggressive thresholds in response to aggressive calls I consider the latter response to be an example of sensitization a behavior that has been documented infrequently in vocalizing anurans Sensitization is a plausible mechanism responsible for the high levels of aggressive calling observed in this species Given the high costs of aggressive calling however it is unclear why a mechanism that increases aggressive call output would be maintainedI would like to thank Flávia Barbosa and Carl Gerhardt for their support and helpful comments on the experimental design and along with Dave Geary the manuscript Two anonymous reviewers provided additional helpful commentary on the manuscript which greatly clarified the text John Christy served as the sponsor of this project at the Smithsonian Tropical Research Institute I thank the staff of STRI for assistance with logistics and permits and the government of the Republic of Panama for providing permission to carry out this project Kathryn Kettenbach assisted with analysis of recordings Financial support was provided by a Smithsonian Institution 10week predoctoral fellowship and a Graduate Assistance in Areas of National Need fellowship from the University of Missouri The experimental protocol was approved by the Institutional Animal Care and Use Committees of the University of Texas IACUC protocol no 06051202 and the Smithsonian Tropical Research Institute IACUC protocol no 200608070706
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