Gene and allele specific expression during electric organ ontogeny in African weakly electric fish and hybrid
Hybridization can act as a catalyst for rapid phenotypic evolution by introducing novel allelic combinations, which can affect hybrid phenotype through changes in gene expression. The African weakly electric fish use their muscle-derived electric organ to produce electric organ discharge (EOD) for electrocommunication and electrolocation. The EOD in genus Campylomormyrus and cross-species hybrids is usually species-specific and varies during ontogeny. We compared the gene expression patterns and allele specific expression between juvenile and adult individuals in C. compressirostris (EOD duration 0.4 ms in juvenile and 0.4 ms in adult), C. rhynchophorus (EOD duration 5 ms in juvenile and 40 ms in adult) and their hybrid (EOD duration 0.4 ms in juvenile and 4 ms in adult). Differentially expressed genes between juveniles and adults were highly enriched in “membrane”, “plasma membrane” and “cytoplasm” Go Ontogeny terms. We detected several potassium channel-related genes (e.g. KCNJ2, ADCYAP1) that are potentially involved in the EOD development during ontogeny. The alleles from C. compressirostris show dominant expression in the hybrid at juvenile and adult life stages. KCNJ2 is the only gene that exhibits allelic dominance of C. rhynchophorus allele, and has an increasing expression during ontogeny in this allele. This suggests that the EOD development in hybrids could be related to the increasing allelic expression of the C. rhynchophorus allele under the scenario of overall dominance of C. compressirostris alleles. Our study sheds light in the evolution of the electric organ discharge in electric fishes and on the role of introgressive hybridization in complex phenotypic traits. Overall design: All juvenile samples were artifically bred and raised at the Univerrsity of Potsdam. Those fish were anesthetized by a lethal dose of clove oil, and dissected on cold 99% ethanol.  Electric organ tissue from each specimen were flash frozen in liquid nitrogen, and further preserved in -80°C.