Gene and allele-specific expression during electric organ ontogeny in African weakly electric fish (Campylomormyrus).

The African weakly electric fish use their muscle-derived electric organ to produce electric organ discharge (EOD) for electrocommunication and electrolocation. The EOD among species of the genus Campylomormyrus and cross-species hybrids is species-specific and varies during ontogeny. We compared the gene expression patterns and allele-specific expression between juvenile and adult in C. compressirostris (EOD duration 0.4 ms in both juveniles and adults), C. rhynchophorus (EOD duration 5 ms in juveniles and 40 ms in adults) and their hybrids (EOD duration 0.4 ms in juveniles and 4 ms in adults). By clustering the gene expression and EOD duration, we identified several candidate genes that might be involved in EOD development, i.e., KCNJ2, CPNE7 and CADPS. In the hybrids, the alleles from parental species show nearly equal expression at both juvenile and adult life stages. KCNJ2 exhibits allelic dominance of the C. rhynchophorus allele, with further increasing expression during ontogeny. This suggests that the EOD development in hybrids could be related to the increasing allelic expression of the C. rhynchophorus allele. Our study sheds light on the evolution and ontogeny of the EOD in electric fishes and on the potential of hybridization to understand the molecular underpinning of complex phenotypic traits.