Understanding the ontogeny & characterizing male sociality in Plains Zebras (Equus Quagga)

Abstract

The structure of animal societies is impacted by the individual components make it. These components are the relationships that form between group members. These relationships vary because individuals have different evolutionarily dictated needs and goals. In complex societies where individuals interact with each other over time and in different contexts, individual “style” or “personality” (defined as behaviors that remain consistent over time and in different contexts) can also have an impact. Most studies of complex societies have not considered or studied how individual variation in social behavior develops and how it impacts other factors of an individual’s life, such as fitness consequences. In this study, we attempt to address these shortcoming by examining male sociality in plains zebras (Equus quagga). Plains zebras have a complex two-tiered society characterized by both smaller, long-term breeding groups called harems and larger, more transient herds composed from multiple harems and bachelor groups. By reconstructing the immediate social environments of 23 focal individuals using Nearest Neighbor data and calculating a “sociality score” from three different node-level measures of sociality (degree centrality, betweenness centrality, and eigenvector centrality), we can understand how the focal males vary in their sociality with conspecifics when they have different reproductive statuses by assigning each individual a sociality score as a bachelor and a stallion. When male-female interaction data is combined with male-male interaction data, we can group stallions in four alternative social styles: Asocial, Gregarious, Female-Focused, and Male-Focused. We propose six hypotheses for potential drivers of stallion social style and find that individuals who are highly male focused as bachelors tend to become stallions who do not evenly interact with males and females as they either remain male focused or become asocial entirely. In contrast we find that those who are not strongly connected to other males as bachelors tend to be the individuals who bond strongly to their harem females. We find no relationship between harem size, a proxy for reproductive success, and stallion sociality style. This has important implications for our understanding of adult male behavior as it suggests that adopting alternative social styles doesn’t seem to have a consequence for male fitness.