Personality, social environment, and maternal-level effects: insights from a wild kangaroo population

Abstract

The study of animal 'personality', or consistent individual differences in behaviour, has received much attention in the last two decades, but several important questions remain unclear. In particular, how important is individual personality in shaping behaviour, relative to the effects of an individual's immediate social environment? What is the interplay between individual and group effects on behavioural variation: in particular, for social species, is variation between groups in behaviour shaped by the personalities of key individuals, or by all individuals in a group? And how early in life are consistent differences in behaviour between individuals detectable? In this thesis, I address these issues using a study of a population of wild eastern grey kangaroos (Macropus giganteus Shaw 1790) in Victoria, Australia, in which marked individuals have been monitored since 2008. Eastern grey kangaroos are social animals living in fusion-fission groups, and previous work on the species has shown evidence of repeatable individual variation in behaviour, or 'personalities'. However, previous personality analyses in this species did not consider the role of among-group variance in behaviour, and were limited to adult females. There is also very little known - for any species - about the effect of among-mother variance on the behavioural differences found between individuals, and hence of the contribution of maternal effects to the magnitude of individual repeatability. Here, I used a combination of experimental tests and behavioural observations to address three main questions: (1) What is the relative importance of individual repeatability versus among-group variance in behavioural responses to a series of experimental stimuli? (2) Are group-level responses driven by collective behaviour of all individuals in the group, or by the behaviour of particular individuals? (3) How early in life is among-individual variance in behaviour apparent, and to what extent is it shaped by maternal-level effects causing differences between offspring of different mothers? The thesis provides a comprehensive illustration of the importance of considering social context when studying animal behaviour in the wild, building on and contributing to work in the fields of behavioural and evolutionary ecology. It is composed of five chapters: a general introduction, three data chapters, and a general discussion. In the introduction, I establish the rationale for the boundaries of my research through a comprehensive literature review. In the data chapters, I address the three main questions listed above, for which I used phenotypic data on over 300 individual eastern grey kangaroos across a decade; hence, the data chapters are interconnected parts of a single large piece of work. Finally, in the discussion, I set up the general considerations, limitations, and next steps from my work. Show more