Meeting Abstract
Species that exhibit alternative male reproductive tactics (ARTs) offer an outstanding opportunity to explore the neural and hormonal mechanisms that underlie often extreme divergence in brain and behavior within a sex. Plainfin midshipman fish, Porichthys notatus, exemplify such male ART divergence in vocal courtship, territoriality and aggression with correspondingly dimorphic brain, somatic and hormonal phenotypes. Across vertebrates these behaviors are modulated by brain monoamines, which include serotonin (5-HT), and the catecholamines (CA) dopamine and noradrenaline. Focusing on discrete monoaminergic nuclei and the well-delineated intrasexually dimorphic vocal circuitry in this species, we investigated if brain monoamines provide additional neural substrates underlying divergence in reproductive behavior between male ARTs. Indeed, high 5-HT and low CA innervation in the vocal hindbrain is characteristic of the highly vocal, aggressive, territorial “type I” phenotype while the reverse pattern is seen in sneaker “type II” males, suggesting excitatory vs inhibitory action of 5-HT and CA, respectively, on vocal motor neuron output. In contrast, larger 5-HT-ir cell volume to body size ratio in type II males is consistent with a predictably higher serotonergic tone in the non-territorial, comparatively non-aggressive males. In addition, acoustic playback experiments coupled with markers for neuronal activation indicate both similarities and differences in CA responses between ARTs and suggests intrasexual divergence in social acoustic signal processing.
