Social decision-making in a group living cichlid fish

Abstract

<p>For my doctoral research I examined social decision-making in a cooperatively breeding cichlid fish, <em>Neolamprologus pulcher</em> with a focus on affiliation and aggression. I investigated the role that the nonapeptide hormone, isotocin, plays in modulating social decisions in these contexts. I show that <em>N. pulcher</em> males prefer to join larger groups regardless of the rank at which they will join, whereas females prefer larger groups only when they can join a group in a high rank (Chapter 2). I examined decision-making during resource contests in<em> </em>(Chapter 3) and found that <em>N. pulcher</em> are sensitive to the size of their opponents, making fighting decisions depending on their opponents’ body size. I also found that smaller <em>N. pulcher</em> are more motivated to persist within contests, showing a shorter latency to resume fighting following interruption (Chapter 4). In Chapters 5 and 6, I explored the role of isotocin (the teleost fish homologue of oxytocin) in regulating social behaviour. I discovered that an increase in isotocin increased responsiveness to social information. Fish treated with isotocin were more sensitive to their opponent’s size in contests and were more submissive to dominant individuals within their social group (Chapter 5). Unexpectedly, I found that exogenous isotocin reduced sociality in <em>N. pulcher, </em>and that an isotocin receptor antagonist increased it (Chapter 6). These results suggest that the relationship between isotocin and social behaviour is both complex and context specific. In my final data chapter, I used social network analysis to explore the role of dominance interactions in determining the structure of <em>N. pulcher</em> social groups. I found that <em>N. pulcher</em> dominance hierarchies are highly linear, but that dominance interactions are not predicted by sex or body size asymmetry (Chapter 7). I found that conflict within <em>N. pulcher</em> social groups is greatest at the top of the dominance hierarchy. Taken together the results of my thesis helps to elucidate the behavioural and hormonal basis of social decision-making in a cooperatively breeding vertebrate and help to illuminate the evolution of social behaviour.</p>