Weakly Electric Fish Dominance
The use of electrocommunication to mediate dominance hierarchies and aggressive encounters has been shown in both pulse-type and wave-type fish. Electrocommunication in these contexts has been related to hormones and even to social history in at least one species, Brachyhypopomus gauderio (Gebhardt et al. 2012, 623; Fugère et al. 2011, 197; Salazar & Stoddard 2009, 399; Cuddy et al. 2012, 4; Raab et al. 2019, 1). Weakly electric fish seem to use different EOD frequencies, EOD lengths, and IDI patterns as competitive indicators for establishing dominance hierarchies and in bouts of ritualised aggression (Gebhardt et al. 2012, 623; Fugère et al. 2011, 197; Salazar & Stoddard 2009, 399; Cuddy et al. 2012, 4; Raab et al. 2019, 1). Research into dominance and aggression has focused largely on wave-type fish (Fugère et al. 2011, 197; Salazar & Stoddard 2009, 399; Cuddy et al. 2012, 4; Raab et al. 2019, 1). In the Sternarchrohynchus genus, EOD frequency has been correlated with body size, and it seems that fish with higher EOD frequencies are dominant over fish with lower EOD frequencies regardless of sex (Fugère et al. 2011, 198). In contrast, the role of EOD frequency in establishing dominance has only been shown in male A. leptorhynchus (Cuddy et al. 2012, 4). Males with higher EOD frequency are dominant and show increased 11-ketotestosterone levels, an important hormone in male electrocommunicative aggression and courtship (Cuddy et al. 2012, 10). However, this study also found that type 2 chirps previously characterised as purely aggressive signals, in fact, do not serve a threatening purpose but may instead signal submission in A. leptorhynchus (Cuddy et al. 2012, 10). It also revealed that type 1 chirps, delineated prior as courtship signals, do not serve this purpose (Cuddy et al. 2012, 10). In holding with this pattern, A. leptorhynchus males with higher EOD frequencies spend more time in habitats that provide good shelter, and are more explorative than males with lower EOD frequencies (Raab et al. 2019, 7). This is likely due to territoriality. Lower EOD males often have to look for new shelter when they lose dominance bouts against higher EOD males which have secured a higher quality territory (Raab et al. 2019, 8).