Causal Feedbacks and the Ecology and Evolution of Social Relationships in Northern Bottlenose Whales

Abstract

Social relationships are ubiquitous in the animal kingdom, though we are just beginning to understand their evolutionary origins and how they affect other aspects of biology. My thesis aims to understand the ecology and evolution of social relationships through an Endangered population of northern bottlenose whales (Hyperoodon ampullatus). Using field data spanning 37 years, my work provides new insights into the generality of key ideas in behavioural ecology. I begin by developing a new framework for quantifying bidirectional effects, such as co-evolutionary feedback or eco-evolutionary dynamics. This chapter bridges a major gap between theory and methodology in both ecology and evolution, highlighting new ways to analyze observational data. Next, I examine the structure of associations between individuals, finding new evidence of decades-long relationships among whales. These relationships are not shaped by kinship, in contrast to most studied mammalian societies. I then consider social connections across the lifetime, finding that older male northern bottlenose whales are socially isolated compared to their younger counterparts, mirroring declines in social connection seen in humans and other animals. Surprisingly, females appear to become more social with age, providing rare evidence that social ageing can be sex specific. I then apply methods designed to investigate causal feedback to the study of social behaviour in northern bottlenose whales. On a short-term ecological scale, I explore how social and spatial relationships in the whales change through time. In doing so I discover that sex and age influence space-use, with evidence of a potential nursery habitat. On a long-term evolutionary scale, I explore the phylogenetic origins of social complexity using a comparative model of social network structure. I find that life history and social structure co-evolved across the 34-million-year history of toothed whales, highlighting the central role of social relationships in shaping other aspects of biology. Together, this work illustrates how long-term ecological research and new methods for causal inference can be combined to understand the origins and functions of sociality.