Scale dependent processing of conspecific signals in the gray treefrog Hyla versicolor
Acoustic communication is both widespread and often essential for successful mate selection, territorial defense, and many social behaviors in many taxa. Laboratory studies often use ‘simplified’, artificial stimuli which have high signal-to-noise rations and are easy to manipulate, but often do not capture the true range and variation of sounds experienced by organisms in the field. In nature, acoustic signals from socially aggregating animals are often emitted together, clustered in space and time. As these signals come from conspecifics they tend to be self-similar in many parameters, providing a challenge for the auditory system to detect, localize, and discriminate between target signals amongst the background. Additionally, signal-environment interactions during transmission further increase the difficulty. In this dissertation, I explore the processing of natural signals in the eastern grey treefrog, Hyla versicolor. During the mating season, numerous males gather near water sources and form choruses, emitting a stereotyped advertisement calls, creating a challenging auditory environment. Females later approach the chorus from daytime resting sites, often up to several hundred meters distant. Females must first detect and orient to the chorus, and subsequently detect, localize, and discriminate among individual male calls embedded in the chorus background. In chapter 2, I quantify the attraction of the chorus using recordings made at increasing distances from a single calling male. In the field, females oriented to the chorus at distances up to 100 m. In laboratory playback experiments, females were only attracted to chorus recordings made up to 32 m from a male. Chapter 3 explores whether sound amplitude or temporal structure degradation, dynamic acoustic features that changes with distance to a calling male, has a greater impact on chorus attractiveness and orientation. Through playback experiments we found that distance-dependent changes in call temporal structure had a larger effect on signal attractiveness than sound level, and that localization accuracy was proportional to sound level, signal attraction was not. This supported the necessity of perceptible fine temporal structure (pulse rise/fall time, pulse duration, etc.) in calls for female localization and discrimination, and that this information is probably not present at distances greater than 32 m. Finally, chapter 4 describes the representation of synthetic calls and natural chorus sounds in the central auditory system of H. versicolor. Single midbrain neurons had diverse response properties, including rapid, slow, and intermediate firing rate adaptation in response to stimuli, which resemble phasic, tonic, and phasi-tonic responses found in other anuran studies, respectively. The slowly-adapting cells had the least attenuation with recording distance from a calling male, and for an approaching female would likely be the first cells to respond to the chorus itself, or individual male calls embedded within. Rapidly-adapting cells, which demonstrate strong attenuation with distance and strong on/offset properties to call pulses are well positioned to aid in the detection of nearby individual male calls and the discrimination of temporal features essential for mate selection, which most likely take place at distances of no more than 4-8 m from a male calling in a dense chorus. Overall, we have just begun to explore auditory behavior and physiology with significant attention to the real-world context of the animal. The results of these studies demonstrate both the strict limits nature places on sensory systems, and their adaptability to the needs of the organism.
Acoustic communication, Animal behavior, Amphibian, Animal communication, Anuran, Auditory biology, Auditory neuroscience, Field behavior, Hearing in noise, Laboratory behavior, Orientation, Phonotaxis, Neurophysiology, Noise, Sound localization
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign