Tolerant pattern recognition: evidence from phonotactic responses in the cricket <i>Gryllus bimaculatus</i> (de Geer).

Abstract

When the amplitude modulation of species-specific acoustic signals is distorted in the transmission channel, signals become difficult to recognize by the receiver. Tolerant auditory pattern recognition systems, which after having perceived the correct species-specific signal transiently broaden their acceptance of signals, would be advantageous for animals as an adaptation to the constraints of the environment. Using a well-studied cricket species, <i>Gryllus bimaculatus</i>, we analysed tolerance in auditory steering responses to '<i>Odd</i>' chirps, mimicking a signal distorted by the transmission channel, and control '<i>Silent</i>' chirps by employing a fine-scale open-loop trackball system. <i>Odd</i> chirps on their own did not elicit a phonotactic response. However, when inserted into a calling song pattern with attractive <i>Normal</i> chirps, the females' phonotactic response toward these patterns was significantly larger than to patterns with <i>Silent</i> chirps. Moreover, females actively steered toward <i>Odd</i> chirps when these were presented within a sequence of attractive chirps. Our results suggest that crickets employ a tolerant pattern recognition system that, once activated, transiently allows responses to distorted sound patterns, as long as sufficient natural chirps are present. As pattern recognition modulates how crickets process non-attractive acoustic signals, the finding is also relevant for the interpretation of two-choice behavioural experiments.