Meeting Abstract
The Elastic Spring Apparatus (ESA), composed of the protractor muscle (PM) and a modified process of the fourth vertebra (i.e. Müllerian ramus), evolved independently in several catfish families. In most taxa, its function is sound production, but the PM of some synodontid mochokids has been modified to produce electric discharges. Here, we compare the ESA behavioral phenotype, morphology, and associated neural circuit between three synodontid species producing sounds (Synodontis grandiops), electric discharges (S. nigriventris), or both (S. eupterus) and representative members of two sister genera – Microsynodontis batesii and Mochokiella paynei. Microsynodontis batesii and M. paynei produce only sounds suggesting that electric signaling evolved only among synodontids. Together, the ESA of the five species shows large interspecific differences in size and shape including intergeneric differences in the PM insertion points, while S. nigriventris has the thinnest PM and a Müllerian ramus with the longest stem and shortest plate. Despite some quantitative differences, tract tracing after labelling of the PM with neurobiotin or dextran biotin reveals similar organizational patterns in the ESA neural circuit for the five species. In every case, paired motor and premotor nuclei are positioned at the same location in the caudal hindbrain. Despite dramatic differences in the behavioral phenotype and anatomy of the ESA, the central ESA neural circuit of these five species seems highly conserved. Research support from the NSF (IOS-1656664 to AHB), DFG (BPC), and F.R.S-FNRS (LK).
