Gene and allele specific expression underlying the electric signal divergence in African weakly electric fish

Abstract In the African weakly electric fish genus Campylomormyrus , electric organ discharge (EOD) signals are strikingly different in shape and duration among closely related species, contribute to pre-zygotic isolation and may have triggered an adaptive radiation. We performed mRNA sequencing on electric organs (EOs) and skeletal muscles (SMs; from which the EOs derive) from three species with short (0.4 ms), medium (5 ms), and long (40 ms) EODs and two different cross-species hybrids. We identified 1,444 up-regulated genes in EO shared by all five species/hybrids cohorts, rendering them candidate genes for EO-specific properties in Campylomormyrus . We further identified several candidate genes, including KCNJ2 and KLF5 , their up-regulation may contribute to increased EOD duration. Hybrids between a short ( C. compressirostris ) and a long ( C. rhynchophorus ) discharging species exhibit EODs of intermediate duration and showed imbalanced expression of KCNJ2 alleles, pointing towards a cis-regulatory difference at this locus, relative to EOD duration. KLF5 is a transcription factor potentially balancing potassium channel gene expression, a crucial process for the formation of an EOD. Unraveling the genetic basis of the species-specific modulation of the EOD in Campylomormyrus is crucial for understanding the adaptive radiation of this emerging model taxon of ecological (perhaps even sympatric) speciation.