Comparative histology of the adult electric organ among four species of the genus Campylomormyrus (Teleostei: Mormyridae)

Abstract

The electric organ (EO) of weakly electric mormyrids consists of flat, disk-shaped electrocytes with distinct anterior and posterior faces. There are multiple species-characteristic patterns in the geometry of the electrocytes and their innervation. To further correlate electric organ discharge (EOD) with EO anatomy, we examined four species of the mormyrid genus Campylomormyrus possessing clearly distinct EODs. In C. compressirostris, C. numenius, and C. tshokwe, all of which display biphasic EODs, the posterior face of the electrocytes forms evaginations merging to a stalk system receiving the innervation. In C. tamandua that emits a triphasic EOD, the small stalks of the electrocyte penetrate the electrocyte anteriorly before merging on the anterior side to receive the innervation. Additional differences in electrocyte anatomy among the former three species with the same EO geometry could be associated with further characteristics of their EODs. Furthermore, in C. numenius, ontogenetic changes in EO anatomy correlate with profound changes in the EOD. In the juvenile the anterior face of the electrocyte is smooth, whereas in the adult it exhibits pronounced surface foldings. This anatomical difference, together with disparities in the degree of stalk furcation, probably contributes to the about 12 times longer EOD in the adult.

Signal diversification is associated with corollary discharge evolution in weakly electric fish

“…6). A previous 490 study demonstrated that EOD duration changes substantially with growth in C. numenius, and 491 this correlates with ontogenetic changes in EO anatomy (Paul et al, 2015). For many mormyrid 492 species, EOD waveform varies with ontogeny, sex, relative dominance, and season (Bass, 1986;493 Hopkins, 1999;Carlson et al, 2000;Werneyer and Kramer, 2006).…”

“…We grouped EODs of C. numenius into three arbitrary types based on variation in 149 duration (Long, Intermediate, and Short EOD), following a previous study that revealed 150 extensive individual variation in EOD duration within this species (Paul et al, 2015). In the 151 following analysis, we used the average value without separating types.…”

Transcriptome-wide single nucleotide polymorphisms related to electric organ discharge differentiation among African weakly electric fish (genus Campylomormyrus)

“…Mormyrids evolved an electric organ enabling them to produce electric organ discharges (EODs) for orientation and communication, i.e., mate recognition and species discrimination [9][10][11][12][13][14]. The main structure of electric organs is formed by tens of specialized cells, called electrocytes, which have a disk-like shape and are stacked in cylindrical columns [15][16][17][18][19][20][21].…”

“…Either the anterior or the posterior face of electrocytes gives rise to several finger-like evaginations fusing in a stalk, serving as the interface to the electromotor neuron. Those stalks can penetrate the electrocyte and occur as single-or multiple stalk-systems [15][16][17][18]. The electrocyte faces can be smooth or unevenly invaginated with papillae or folds increasing the membrane's surface [15,16].…”

“…In mormyrids, there is evidence that different patterns of electrocyte geometry, like electrocyte penetrations, cause different EOD waveforms. The electric organ of several mormyrid species has been histologically analyzed and a relation between electrocytes being stalk-penetrated or not and the EOD phase number could be observed [15][16][17][18][19]. Further, species with a multiple-stalk system are found to have a longer EOD than those with a single-stalk system [19].…”