SOCIAL ENVIRONMENT MODULATES THE FUNCTION AND NEUROENDOCRINE REGULATION OF ELECTROCOMMUNICATION SIGNALS ACROSS SPECIES OF APTERONOTID FISHES

Abstract

Because communication is inherently social, signals and social behavior should coevolve. Physiological regulation of signal production and perception should also be linked to social evolution. South American weakly electric knifefishes are an excellent system for investigating neuroendocrine mechanisms that coregulate sociality and sensorimotor systems responsible for communication. Knifefishes produce electric organ discharges that they modulate to produce signals called chirps. In this dissertation, I first found that species’ sociality does not explain variation in chirp structure complexity. I next asked how context influences production and neuroendocrine regulation of chirps across three species that vary in sociality: territorial Apteronotus albifrons, semi-social Apteronotus leptorhynchus, and gregarious Adontosternarchus balaenops. I recorded fish overnight in isolation, in same-sex pairs, and in opposite-sex pairs. I collected blood and brains to measure circulating steroid hormones and gene expression for several neuromodulator receptors in electrosensory brain regions. Semi-social A. leptorhynchus chirped more than the other species. Males chirped more in A. leptorhynchus and in A. albifrons. Chirping was sexually monomorphic in A. balaenops. While chirping, hormone levels, and neuromodulator gene expression did not vary consistently with social context, they covaried with species and individual condition. Reproductive condition in A. albifrons and A. balaenops, but size in A. leptorhynchus, explained male chirp rates and gonadal steroid levels. Social cortisol levels were negatively correlated with individual condition in the territorial species. Abundance of eight neuromodulator receptor genes varied in two electrosensory brain regions across species. vi i Gregarious A. balaenops often had the lowest, while territorial A. albifrons often had the highest gene expression. Gene expression profiles and correlations among gene pairs were nonoverlapping across species and context. Despite the potential for social complexity, A. balaenops were less behaviorally and physiologically variable. Perceiving conspecific signals during the less predictable social interactions common in A. albifrons aggressive, territorial encounters or in A. leptorhynchus dominance hierarchies may be more critical for survival and reproductive success. Individuals may not need to be as responsive in stable groups of A. balaenops. This dissertation highlights that how variation in communication maps onto variation in social behavior differs across levels of biological control and is highly-context dependent.