The dynamics of cleaner-client interactions

Mutualisms involve beneficial interactions between species and link every eukaryote on the planet. Despite their pervasiveness, however, it is not clear why these interactions evolved and are so ubiquitously maintained. Cleaning is an iconic mutualism and involves a cleaner species, often a fish, removing ectoparasites and other material from the body of a heterospecific (termed a client): cleaners gain a food source, whilst the clients’ health can benefit from parasite removal. This study aimed to contribute to knowledge on the evolution and persistence of mutualisms by asking: how pervasive is cleaning across the animal kingdom, and what factors can influence the pervasiveness (Chapters 2 – 4) and dynamics (Chapters 5 – 8) of the interaction at an individual, population and species level. Mutualisms are complex and dynamic interactions, and this study identified a suite of contextual factors that can influence the pervasiveness and patterns of the interaction (Chapter 2). In situ, the availability of specific food resources, spatial location and the abiotic environment influenced the occurrence of cleaning (Chapters 3 and 4). Using a long-term 8 year data set collected on cleaner-client interactions on the same Caribbean reef, Chapters 5 and 6 showed that even within the same environment, cleaning patterns can vary temporally, spatially and, across and within client identities. Chapter 6 subsequently found that the abundance and diversity of clients (cleaner choice options), consistently regulated cleaning frequencies. The importance of both cleaner and client choice in governing who interacts with whom and how, was also found, at an individual level (Chapters 7 and 8). Together, this study highlights how sensitive cleaning interactions are to changing contexts, and how their occurrence and functioning, relies on the wide abundance, diversity and variable behaviour of clients. As Chapter 4 shows, iconic cleaning interactions are not immune to breakdowns, and coral reefs are currently one of the most threatened ecosystems on Earth, experiencing sharp declines in species abundance and diversity. It is not clear whether cleaning will be maintained as a food acquisition behaviour under future environmental conditions