Effects of the Brain Nonapeptides Arginine-Vasotocin and Isotocin on Shoaling Behaviour in the Guppy (Poecilia reticulata)
Abstract
Brain nonapeptides have been suggested to regulate social behaviours. However, the contribution of Arginine-Vasotocin (AVT) and Isotocin (IT) to social behaviour in fishes is not well-characterized. Using the guppy (Poecilia reticulata), I first measured association preference for conspecifics in individuals injected with either AVT, an AVT-antagonist, or saline. The time spent associating with conspecifics did not differ significantly among the injection treatments. However, individuals injected with AVT performed more movement among areas of the tank than individuals injected with either the AVT-antagonist or saline, consistent with an effect of AVT on anxiety-related behaviours (i.e. hyperactivity). Second, I measured association preference for conspecifics in individuals injected with IT and an IT-antagonist. Individuals injected with IT spent more time associating with conspecifics than individuals injected with an IT-antagonist, consistent with a positive relationship between IT on shoaling. Third, I compared shoaling behaviour between a high- and a low-predation population and between sexes. Individuals from a high-predation population spent more time associating with conspecifics than individuals from a low-predation population, and females spent more time than males associating with conspecifics. Movement did not differ significantly between populations and sexes. Brain AVT and IT immunoreactivity measurements showed that AVT intensity in the gigantocellular neurons in the preoptic area was higher in individuals from the high-predation population. I found no difference in IT intensity between the two populations and no difference between the sexes in AVT and IT intensity. Finally, I examined the distribution of AVT receptors in the brain of individuals of mixed populations and sexes showing potential sites of action for AVT in the telencephalon, diencephalon, mesencephalon, and rhombencephalon. Overall, my study suggests a role of IT in shoaling behaviour, albeit IT intensity in the preoptic area was not associated with shoaling differences across populations and sexes. I did not observe an effect of AVT on shoaling, but instead showed a positive relationship between AVT and an anxiety-related behaviour, as well as greater AVT intensity in a population with high predation, which suggests the potential of AVT-associated fear as an important response to differences in predation.