Personalities, social patterns, and reproductive success in female eastern grey kangaroos (Macropus giganteus)

Abstract

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...