| Popis: |
This dissertation reports on a study conducted to examine the morphological, behavioral, and environmental sources of variation in the structure of house cricket, Acheta domesticus, calling song. Song variations may be important in female mating decisions and influence male mating success. Eleven song parameters were measured: chirp duration, interchirp duration, syllable number, syllable duration, intersyllable duration, mean frequency, frequency intensity, minimum frequency, maximum frequency, syllable intensity, and intensity difference between syllable and frequency intensity. Morphological factors examined included body: mass, length, color, asymmetry, intactness; and male age. Behavioral factors were timing of song bouts and proclivity to sing. Environmental conditions of high population densities were simulated by temporarily placing males into an arena with three other males. The calling song structure of tactilely isolated males resulted in three factors: frequency (mean, minimum, and maximum frequencies); intensity (syllable intensity, and intensity difference); and variability (difference between syllable intensity and frequency intensity). Males with high body intactness sang at lower frequencies. Asymmetrical males sang more intense songs. Large males sang with more intensity and frequency variability. Intermale competitions resulted in distinguishable linear dominance hierarchies. Lower-ranking males sang less often than higher-ranking males, altered singing times, and sang quieter songs. Intermale competition resulted in males altering song structure. Analysis of post-competitive songs resulted in three factors: frequency (mean and maximum frequencies, and intensity difference); energy (duty-cycle, intensity, and minimum frequency) and variability (unchanged). Higher-ranking asymmetrical males sang at lower frequencies. Higher-ranking males sang with greater energy, and timed their singing to female receptive times. Higher-ranking, large, intact males sang with less variability. This study indicated that A. domesticus males signal phenotypic information via their calling song characteristics. More specifically, in low population densities males signal information concerning their fitness-related qualities. After having established dominance orders, the male signal information concerning their rank in conjunction with fitness. The implications of this study were that intermale competition altered the song cues available to the females and may alter female mating decisions. |
