In social mammals, social integration is generally assumed to improve females' reproductive success. Most species demonstrating this relationship exhibit complex forms of social bonds and interactions. However, female eastern grey kangaroos ( Macropus giganteus ) exhibit differentiated social relationships, yet do not appear to cooperate directly. It is unclear what the fitness consequences of such sociability could be in species that do not exhibit obvious forms of cooperation. Using 4 years of life history, spatial and social data from a wild population of approximately 200 individually recognizable female eastern grey kangaroos, we tested whether higher levels of sociability are associated with greater reproductive success. Contrary to expectations, we found that the size of a female's social network, her numbers of preferential associations with other females and her group sizes all negatively influenced her reproductive success. These factors influenced the survival of dependent young that had left the pouch rather than those that were still in the pouch. We also show that primiparous females (first-time breeders) were less likely to have surviving young. Our findings suggest that social bonds are not always beneficial for reproductive success in group-living species, and that female kangaroos may experience trade-offs between successfully rearing young and maintaining affiliative relationships.

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Animal social behaviour can have important effects on the long-term dynamics of diseases. In particular, preferential spatial relationships between individuals can lead to differences in the rates of disease spread within a population. We examined the concurrent influence of genetic relatedness, sex, age, home range overlap, time of year, and prion disease status on proximal associations of adult Rocky Mountain mule deer (Odocoileus hemionus hemionus) in a chronic wasting disease endemic area. We also quantified the temporal stability of these associations across different sex, age, and disease status classes. We used three years of high frequency telemetry data from 74 individuals to record encounters within 25 m of each other, and to calculate seasonal home range overlap measured by volume of intersection (VI). The strength of pairwise spatial association between adult mule deer was independent of genetic relatedness, age and disease status. Seasonal variation in association strength was not consistent across years, perhaps due to annual changes in weather conditions. The influence of home range overlap on association strength varied seasonally, whereby associations were stronger in pre-rut and fawning than in the rest of the seasons. The sexes of individuals also interacted with both VI and season. At increasing levels of VI, associations were stronger between females than between males and between females and males. The strongest associations in pre-rut were between males, while the strongest in rut were between females and males. The temporal stability of associations was markedly dependant on the sex and the diagnosis of the associating pair. Our findings highlight the importance of considering concurrent effects of biological and environmental factors when seeking to understand the role of social preference in behavioural ecology and disease spread. Applying this knowledge in epidemiological modelling will shed light on the dynamics of disease transmission among mule deer.

Sociality evolves when the benefits of grouping outweigh the costs. Living with relatives can sometimes help to offset some of these costs, and fission-fusion dynamics can help to maximize benefits. Individual differences in sociability can exist and such differences have been linked to fitness consequences in several species. Differences in other personality traits, those that show within-individual consistency and significant differences among individuals, can also influence fitness. However, more research is needed on the relationships among personality traits, and their fitness correlates, in natural populations to better understand the adaptive nature of individual differences in personality traits.The overall objective of my PhD was to understand some of the constraints, correlates, and fitness consequences of individual differences in sociability in an herbivorous marsupial, the eastern grey kangaroo (Macropus giganteus). Eastern grey kangaroos forage in open-membership groups that frequently change in size and composition. Females show natal philopatry but not complex cooperative interactions. I conducted field observations of a wild population of eastern grey kangaroos in Sundown National Park in south-east Queensland, Australia, over more than two years. I documented life-history traits, grouping patterns, and behavioural responses of over 240 identified females, and analysed these data in addition to two previous years' worth of data collected by other researchers.My first aim (Chapter 2) was to determine the extent to which females' boldness and sociability measures were consistent over multiple years, and how stable correlations among these traits were across time. I also determined whether females' association patterns could be explained to some degree by similarity in boldness, as measured by flight initiation distance. Individual differences in boldness and two measures of sociability (foraging group size and number of preferred associates) were significantly consistent across four years, and correlations between these traits tended to show consistency over time. Some social assortment between females of similar personalities was observed, but this was not consistent over time, and boldness was not related to preferential associations, suggesting that females were not actively choosing to associate with others based on their similarity in personality.In Chapter 3, I explored the relationships between kinship and association strengths among female kangaroos over four years. I used both biparental genetic relatedness estimates and mother-daughter relationships as measures of kinship, and conducted one set of analyses that considered both adults iii and sub-adults, and one restricted to adult females. Both analyses showed weak, yet significant, positive correlations between association strengths and biparental relatedness for all four years.Mother-daughter status of adult females explained almost twice the variation in pairs' association strengths as did biparental relatedness. Although spac...