Vocal behavior and vocal central pattern generator organization diverge among toadfishes

Area of Science:

• Neuroscience
• Bioacoustics
• Ichthyology

Background:

• Acoustic communication is well-studied in toadfish, but comparative studies of vocalization mechanisms are lacking.
• Understanding the neural basis of vocalization is crucial for identifying shared and derived traits in fish communication.

Purpose of the Study:

• To delineate the hindbrain vocal network in the Gulf toadfish (Opsanus beta) using neural tracing and electrophysiology.
• To identify neural circuits responsible for generating specific acoustic parameters like call duration and frequency.

Main Methods:

• Vocal nerve labeling (dextran-biotin, biocytin, neurobiotin) to trace neural pathways.
• Intracellular in vivo recording and staining of motoneurons and premotor neurons.
• Analysis of neural activity patterns in relation to vocal nerve volleys.

Main Results:

• Identified a midline vocal motor nucleus (VMN) and characterized motoneuron morphology and activity.
• Revealed premotor neurons with pacemaker-like activity directly coupled to the vocal motor system.
• Discovered separate neural populations predicting vocalization frequency and duration, with connections to auditory centers.

Conclusions:

• Propose that separate premotor coding of vocal frequency and duration, coupled to auditory nuclei, are ancestral traits in toadfishes.
• Suggest that differences in pacemaker neuron connectivity contribute to species-specific vocalization patterns.
• The study provides a neuroanatomical framework for understanding the evolution of complex acoustic signals in fishes.