Cochlear sensitivity in the lesser spear-nosed bat, Phyllostomus discolor

Area of Science:

• Auditory Neuroscience
• Bioacoustics
• Mammalian Physiology

Background:

• Behavioral studies revealed unusual auditory thresholds in Phyllostomus discolor, with minima and a 55 kHz insensitive region.
• The underlying mechanisms for these thresholds, particularly cochlear contributions, remained unclear.

Purpose of the Study:

• To investigate the role of cochlear mechanics in shaping the auditory thresholds of Phyllostomus discolor.
• To determine if the observed behavioral auditory characteristics are intrinsic to the cochlea or influenced by other auditory system components.

Main Methods:

• Recording of distortion product otoacoustic emissions (DPOAEs) in Phyllostomus discolor.
• Calculation of relative DPOAE threshold curves to assess cochlear sensitivity.
• Assessment of cochlear frequency tuning using DPOAE suppression tuning curves (STCs).

Main Results:

• Cochlear sensitivity, measured by DPOAEs, did not exhibit a threshold maximum at 55 kHz.
• DPOAE threshold curves showed a minimum around 30 kHz, with a continuous increase thereafter.
• Suppression tuning curves indicated broad cochlear filter bandwidths (Q10dB: 3.4–10.7) without frequency-specific specializations.

Conclusions:

• The cochlea of Phyllostomus discolor does not appear to be the primary driver of the complex high-frequency auditory threshold pattern observed behaviorally.
• Outer ear transfer characteristics and/or neural processing likely contribute significantly to the high-frequency auditory perception in this species.
• Behavioral auditory thresholds are not solely determined by cochlear mechanics in Phyllostomus discolor.