The social behavior of electric fishes varies across species. Some species, like black ghost knifefish (Apteronotus albifrons), dragon knifefish (“Apteronotus” bonapartii), and pig-duck knifefish (Parapateronotus hasemani) are highly territorial and aggressive. Other species, like Adontosternarchus devenanzii, are gregarious and social (McNeil et al. 2014). Brown ghost knifefish (Apteronotus leptorhynchus) have dominance hierarchies but are less aggressive than black ghost knifefish. Within species, fish also communicate in a number of different social contexts that can vary with sex, reproductive state, status, and social experience. We are investigating how differences in sociality and social context underlies the variation in how electrocommunication signals are produced, perceived, and regulated during different types of social interactions. Hormones and neuromodulators often control sex and species differences in electrocommunication signals. These modulators are also likely to influence how fish use and process signals in different social environments. By examining how steroid hormones and neuromodulator receptor gene expression in electrosensory brain regions change in response to social experience, we aim to identify the mechanisms underlying the evolution of chirp diversity and function.

We study the influence of social environment and sociality on chirping by using multiple approaches:

(1) Comparing chirp function in different social contexts. Social complexity often necessitates signal complexity in gregarious communication systems, where remembering individual identity and social partners might be particularly important. (Matrosova et al. 2011, Pollard and Blumstein 2012). We are trying to identify how chirp dynamics vary across species with different levels of sociality. Fish are paired together in their home tanks with same-sex or opposite-sex conspecifics and recorded overnight to collect data on chirping. We then analyze the temporal dynamics of chirping and compare differences in chirp types and rate across context and species with varying levels of sociality.

(2) Examining how social experience modulates steroid hormone production. Gonadal steroid hormones control sex differences in electrocommunication (Smith et al. 2013). Adrenal steroids can also influence chirping. Similar to social interaction, cortisol treatment increases chirp rate and neurogenesis in the brain region that controls chirping (Dunlap et al. 2002, Dunlap et al. 2006). Our lab is interested in how social experience modulates the production of steroid hormones. We collect blood samples before, during, and/or after short or long-term social interactions to measure levels of cortisol, 11-ketotestosterone, testosterone, and estradiol. By comparing the change in steroid levels across different social environments and species, we can identify the hormonal mechanisms that regulate responses to social experience.

(3) Quantifying steroid hormone and neuromodulator receptor gene expression in sensory brain regions following social interactions. Across vertebrates, neuromodulatory systems in sensory brain areas encode social context and they often vary across species with different social organization (Goodson and Kingsbury 2011). Steroid hormones can also act on sensory structures to regulate the perception of courtship or agonistic communication signals (Sisneros et al. 2004). After a social experience, we have used quantitative PCR to measurd the amount of mRNA for neuromodulator receptors and steroid receptors in sensory brain regions. The electrosensory lateral line lobe (ELL) in the hindbrain receives input from electroreceptors and encodes chirp parameters in the brain. The ELL then projects to the torus semicircularis (Ts) (the teleost homolog of the inferior colliculus), a midbrain structure involved in the higher-order neural processing of communication signals (Vonderschen and Chacron 2011, Marsat et al. 2012). We have found that both the ELL and Ts express genes for gonadal steroid hormone receptors and metabolizing enzymes (Freiler et al. 2024), and have also been studying species and sex differences in the expression of receptors for neuromodulators in the ELL and Ts.