Bioacoustic variation of swimbladder disturbance sounds in Neotropical doradoid catfishes (Siluriformes: Doradidae, Auchenipteridae): Potential morphological correlates

Swimbladder disturbance sounds of doradoid catfishes (Doradidae and Auchenipteridae) demonstrated striking waveform and spectrographic variation. We surveyed sounds of 25 doradoid species in 20 genera comparing these to sounds of four vocal outgroup catfish families. Sounds were either continuous waveforms (lacking interpulses) or pulsed (groups of pulses repeated at fixed temporal intervals). This is the first evidence for swimbladder calls with fixed interpulse patterns in catfishes. Vocal mechanism components that were similar between doradids and auchenipterids included: swimbladder shape, swimbladder dimensions and sonic muscle-somatic index. Morphological traits that showed variation among taxa and were evaluated for potential correlates of call diversity are: 1) diverticula (marginal outpocketings of the swimbladder with no connection to inner ear) and 2) elastic spring apparatus Mullerian rami (ESA-Mr). Within the doradid subfamilies and within the Auchenipteridae most species differed significantly in dominant frequency with frequency ranges overlapping to some extent for most. Doradid swimbladder diverticula did not explain dominant frequency variation within the doradoid superfamily. Some doradids with conical ESA-Mr had the highest dominant frequency sounds. Auchenipterids included both relatively lower and higher dominant frequency sound producers but lacked diverticula and had discoidal ESA-Mr. Comparing a phylogeny of doradoid genera with outgroup taxa, we infer that complex diverticula and conical ESA-Mr are derived characters within the Doradidae. Species representing outgroup families produced either continuous lower dominant frequency sounds (aspredinids, mochokids and pseudopimelodids) or pulsed higher dominant frequency sounds (pimelodids) [Current Zoology 58 (1): 171-188, 2012].