Social rank, sex, and context differentially affect electrocommunication, agonistic behavior, and hormones in a weakly electric fish, Apteronotus leptorhynchus

Social environment influences behavior and hormone production in many vertebrate species, with behavior and hormones causing reciprocal, adaptive changes. For example, hormones like androgens (11-ketotestosterone; 11KT) and glucocorticoids (cortisol) both affect and are affected by social dominance interactions. Weakly electric brown ghost knifefish, Apteronotus leptorhynchus&dotbelow;, are a sexually dimorphic, socially polygynous species with hormonally-sensitive electrocommunication. We investigated how social interaction and rank influence communication, agonistic behavior, and hormones (11KT and cortisol) in semi-naturalistic groups of A. leptorhynchus. We measured plasma hormone levels and used playbacks to restrained fish in chirp chambers to elicit electric organ discharge (EOD) modulations (chirps) before and after either one week of social housing or individual housing. Socially housed fish were then tested pairwise in a free-swimming shelter tube competition assay to assess rank, agonistic behaviors, and chirping. Dominant social males increased 11KT levels. Social housing increased EOD frequency in males, but not females. Males chirped more than females to chirp chamber playbacks, as previously reported. However, social males and females chirped at equal rates in live interactions. We showed for the first time that females have a linear dominance hierarchy and that in live, same-sex dyadic trials, subordinate females chirp more than dominant females. Both sexes chirped more when being attacked, but not when attacking others. Taken together, these results suggest that (1) chirping may be a signal of appeasement; and (2) the effects of social interaction on communication and hormones depend on social rank, sex, and context.