Mammalian nonapeptides activate territorial behavior in an amphibian

Arginine vasopressin (VP) and oxytocin (OT) are two nonapeptides present in mammals and execute a wide array of physiological and behavioral functions. In amphibians arginine vasotocin (VT) is hypothesized as a homologous nonapeptide for VP and also performs physiological and behavioral tasks. Studies have demonstrated that the structural and functional relationships between VP, OT, and VT receptor families are similar; however, little behavioral data has complimented these studies. The objective of this investigation was to determine if the mammalian nonapeptides VP and OT would activate behavioral manifestations naturally activated by VT. Frogs are particularly attractive for such an investigation because it is well documented that VT activates advertisement calling and territorial behavior. This investigation was a large sample size field study that utilized the territorial frog, Eleutherodactylus coqui. Fieldwork occurred on the Islands of Puerto Rico and Hawai'i and focused on territorial (calling) and non-territorial (silent) males. Frogs were administered exogenous injections of VP, OT, VT (positive control), or saline (control) in the field, placed back in their original locations, and were observed for behaviors. Exogenous injections of VP and OT significantly activated silent males to emit advertisement calls and exhibit territorial behavior. Additionally, silent males moved into new areas prior to calling whereas territorial males remained in their own territories. Control (saline) males displayed normal behaviors. This is the first study to demonstrate that mammalian nonapeptides activate calling and territorial behaviors in frogs and corroborates the close evolutionary relationships within the nonapeptide family.