Social behavior in South American electric fishes: Linking neuroendocrine Regulation, signal Plasticity, and reproductive strategies

Abstract

Cross-species analysis can provide valuable insights into the neural and hormonal mechanisms underlying behavior. South American weakly electric fishes (order Gymnotiformes) are ideal models due to their well-characterized electric signals, which convey important social information. These signals are quantifiable and traceable to specific brain and peripheral substrates. This review focuses on social electric signaling in two nocturnal gymnotiform species found syntopically in Uruguay: Gymnotus omarorum and Brachyhypopomus gauderio. We examine the influence of sex, social context, and neuromodulators on signal flexibility across day/night and seasonal cycles. Common features include a nocturnal increase in basal electric rate mediated by melatonin, enhancing awareness and social engagement; androgen-mediated seasonal protection of electric signals against high summer temperatures; and the production of social electric signals, such as chirps and interruptions, during social interactions, modulated by vasotocinergic and serotonergic systems. Key differences lie in neuromodulator involvement and signal plasticity: B. gauderio exhibits greater signal flexibility, with sex- and context-dependent waveform changes and a broader repertoire of transient social signals used in dyadic interactions, supported by distinct neural mechanisms. These differences likely reflect species-specific reproductive strategies and their associated costs, such as predation pressure. This review underscores the value of studying electric behavior to understand the integration of internal states with environmental and social cues, offering insights into mechanisms underlying behavioral responses to natural challenges.