Meeting Abstract
Swim bladders have evolved multiple functions not limited to maintaining buoyancy and hydrostatic position in the water column. Direct and indirect connections between the swim bladder and inner ear yield increased hearing abilities when the gas-filled swim bladder transduces pressure-induced vibrations to the inner ear and enables sound pressure detection. In the plainfin midshipman fish, Porichthys notatus, nesting type I males attract females via a multi-harmonic advertisement call known as a ‘hum’. The hum not only attracts females but also type II males or ‘sneakers’ that must also localize type I nests to cuckold and steal fertilizations from type I males that are actively courting females. Recent swim bladder deflation experiments show that the swim bladder is likely necessary for near field sound localization by female midshipman fish. Here we show the first evidence of inter-and intrasexual differences in swim bladder morphology. Micro-CT images reveal bilateral dorsal ‘horn-like’ projections of the swim bladder in both females and type II males which are absent in type I males. Measurements from the rostral most point of the swim bladder to the caudal ends of the three inner ear end organs confirm that females and type II males have significantly shorter distances between these structures than that observed for type I males, strongly suggesting enhanced pressure sensitivity, which may function to increase the detection and localization of vocalizing conspecifics during the breeding season.
