Sexual signalling in bladder grasshoppers: tactical design for maximizing calling range

Area of Science:

• Animal behavior
• Bioacoustics
• Ecology

Background:

• Pair formation in the bladder grasshopper (Bullacris membracioides) involves duetting and male phonotaxis.
• Males use an abdominal resonator for low-frequency stridulatory signals, with females responding using a species-specific time delay.

Purpose of the Study:

• To investigate acoustic transmission of sexual signals in the natural environment of the bladder grasshopper.
• To compare sound propagation under day and night atmospheric conditions.
• To understand adaptations influencing signal range in grasshopper sexual communication.

Main Methods:

• Playback experiments of sexual signals over 450m.
• Measurements of acoustic transmission under diurnal and nocturnal atmospheric conditions.
• Analysis of signal range and environmental factors affecting sound propagation.

Main Results:

• Daytime conditions created upward refraction and a sound shadow zone beyond 50m.
• Nighttime conditions, with downward-refracting temperature inversions, created a 'tunnel effect' enhancing sound transmission.
• Male calling distances increased from 150m in the afternoon to 1.5-1.9km at night, while female calls transmitted a maximum of 50m.
• Significant discrepancy noted in the active space of sex-specific signals.

Conclusions:

• Nocturnal atmospheric conditions significantly enhance grasshopper acoustic communication range.
• Maximizing calling range appears to be a primary selection pressure in this species' sexual signaling system.
• Adaptations in signal characteristics and behavior are key to overcoming transmission challenges and masking noise.