Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Neff, Bryan D

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.

Summary for Lay Audience

Many animals form social groups, but little is known about how the brain regulates the formation of these groups. Nonapeptides are hormones found in the brain that have emerged as potential candidates for regulating social behaviours. In my study, I examined the effect of two nonapeptides—arginine-vasotocin (AVT) and isotocin (IT)—on social behaviour in the guppy (Poecilia reticulata). First, I measured the effect of experimental injections of AVT, IT and inhibitors of those hormones (antagonists) on the amount of time that individuals spent associating with another group of guppies. Next, I measured differences in association behaviour between two populations and sexes and looked at the relationship between behaviour and AVT and IT levels in the brain. Finally, I examined the distribution of AVT receptors in the brain. I found that IT injections led to more association behaviour, while AVT injections had no effect on association. Interestingly, AVT injections were associated with hyperactivity, consistent with a link between AVT and anxiety. Association behaviour was higher for a population where predators were present than a population where predators were absent, and the association was higher for females than males. AVT levels were higher in the population where predators were present and AVT receptor mapping in the brain revealed several areas that may be involved in the effects of this nonapeptide. Overall, my study is one of the first comprehensive studies on the contribution of brain nonapeptide to social behaviours in fish and offered new insights into the mechanisms underlying social behaviours.

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