Are superficial neuromasts proprioceptors underlying fast copulatory behavior?

Area of Science:

• Neuroethology
• Sensory Biology
• Evolutionary Morphology

Background:

• Male Poeciliid fish possess a modified anal fin (gonopodium) crucial for sperm transfer during copulation.
• Gonopodial repositioning involves complex efferent circuitry controlling motor neurons for precise movements.
• The role of cutaneous receptors, specifically superficial neuromasts, in guiding gonopodial positioning remains unknown.

Purpose of the Study:

• To investigate the role of superficial neuromasts in controlling gonopodial positioning and timing during copulation in Western mosquitofish (Gambusia affinis).
• To determine if superficial neuromasts function as proprioceptors in the sexually dimorphic gonopodium.

Main Methods:

• Comparative analysis of superficial neuromast distribution on male and female anal fins.
• Experimental removal of superficial neuromasts surrounding the male gonopodium base.
• Observation and analysis of gonopodial movement patterns and positioning before and after neuromast removal.

Main Results:

• Significantly higher numbers of superficial neuromasts were found around the male gonopodium base compared to the female anal fin.
• Systemic removal of superficial neuromasts led to significant impairments in the positioning and timing of gonopodial movements.
• These findings suggest a sensory role for superficial neuromasts in guiding copulatory actions.

Conclusions:

• Superficial neuromasts surrounding the gonopodium likely function as proprioceptors, contributing to precise spatial awareness and motor control.
• This sensory system appears to have been co-opted during the evolutionary reorganization of the Poeciliid body plan for reproductive purposes.
• The study provides the first evidence for the involvement of cutaneous sensory receptors in the control of gonopodial function during mating.