Social Networks and Fitness Consequences of Early Sociality in Wild Bottlenose Dolphins (Tursiops sp.)

Abstract

Despite recent investigations into the relationship between adult social bonds and fitness in socially complex species, remarkably little attention has focused on the consequences of early sociality. For this dissertation I used social network analysis (SNA) to examine social patterns in wild bottlenose dolphin (Tursiops sp.) calves of Shark Bay, Australia. Bottlenose dolphins exhibit a complex fission-fusion social organization with dynamic group membership and sex-segregation in adult behavior. The extensive Shark Bay dataset provided a unique opportunity to investigate calf social networks and potential fitness consequences of early sociality.

Chapters 1 - 2 discuss challenges in studying sociality and the application of SNA to studies of animal societies with a focus on primates and cetaceans. Chapter 3 presents a case study to illustrate the variety of social measures available to researchers to capture multiple dimensions of social behavior.

Chapter 4 investigates the reliability and precision of common social network metrics. SNA is increasing in popularity, but the error and bias introduced by sample size and method is underappreciated. Social network metrics responded differently to both sample size and method. Also, weighted metrics are arguably appropriate for ameliorating some error.

Chapter 5 uses SNA to investigate social patterns during temporary mother-calf separations. Calves had larger, less dense networks than their mothers, suggesting that calves use these opportunities to expand their networks. Male calves had strong associations with other male calves, foreshadowing adult male alliance formation. Since Shark Bay dolphins exhibit bisexual philopatry, calf associations can last into adulthood and early sociality likely has implications for future success.

Finally, Chapter 6 directly investigates fitness by testing whether calf social networks predict juvenile survival to age 10. Significantly more males died as juveniles; however the probability of male survival increased with the metric eigenvector centrality. Interestingly, as calves, males who died had stronger ties to juvenile males than those males who survived. Thus, while some aspects of early sociality have a fitness benefit, certain associations appear costly. These results suggest that selection is acting on this early life-stage and have implications for the evolution of social behavior and the causes and consequences of sociality.