Non random group assortment is a common phenomenon in many animal societies. It creates a social environment, which can differ widely depending on the mixture of individuals, and on the surrounding ecological environment. In this study I measured the interactions between individual behavioural phenotypes and social structure of the Trinidadian guppy (Poecilia reticulata).
Previous work on wild guppies has shown both negative and positive assortment according to behavioural phenotype in mixed shoals. In Chapters 3 and 6, using replicated semi-natural populations of adult female guppies, I found negative assortment by behavioural phenotype. In Chapter 3 I investigated the effect of heightened predation risk on this pattern of assortment finding females increased
this assortment and formed tighter associations with fewer individuals. This pattern is expected, in light of the evolution of cooperation under predation risk.
Bold and shy individuals differ in their sociability, which I hypothesised would lead to bold and shy fish displaying different social partner preferences. In Chapter 4 I found shy females preferred to associate with bold rather than shy stimulus females, when both were unfamiliar, but bold showed no preference. In Chapter 5 I found that males, which had a tendency to be bolder, preferred bold females
and those with a tendency for shyness preferred shy females when the choice was of females from the same (familiar) habitat. However, the males switched preferences when females were unfamiliar. The implications for cooperation and mate choice are discussed, together with the influence these decisions might have on social network structure.
Finally, influences from within the group, can affect how individuals interact; impacting on the choice of with whom to forage or co-operate. Male harassment, for example, has been shown to increase female's risk of predation and reduce the time spent foraging. In Chapter 6 I investigated the impact of males on the growth of bold and shy females. Shy females showed a slower rate of weight gain
with male introduction to their social environment; whereas bold females showed a reduction when small females were introduced.