The role of colour patterns in a social context: causes and consequences of interspecific variation in anemonefishes

There is remarkable diversity in colour patterns across animal taxa, however, our understanding of the evolution of these colour patterns remains unsolved. Research has focused on a few model species, such as fruit flies, mice and zebrafish, and marine fishes are highly underrepresented. In addition, the majority of studies investigating the functions of colour patterns have explored contexts of natural selection (e.g., camouflage, aposematism) and sexual selection (e.g., mate choice), with social selection (e.g., maintaining group stability) rarely being considered.

In social groups, signalling of social status and individual identity can be important to avoid costly interactions and maintain cooperation. This project aims to provide insight into these social functions of colour patterns and advance our understanding of the evolution of colour patterns across the animal kingdom.

Anemonefishes (Amphiprion spp.) provide a promising model to address such questions. They have complex hierarchical group structures, in which social signalling for maintaining group stability would be beneficial. Their basic ecology is known and they are site attached to anemone hosts, facilitating repeated observations and in-situ experiments.

Anemonefish also display remarkable diversity in colour patterns across species, as well as variation in ecology and social structures. Investigating these species differences will allow exploration of the evolutionary processes that shape diversity in both social structures and colour patterns. This will advance our understanding of the formation and maintenance of complex social groups and the evolution of colour patterns across a wider range of taxa.

The goal of this project is to understanding the social functions of colour patterns in anemonefishes and the causes and consequences of colour patterns in regards to the fishes' social structures. The objectives, approach and hypotheses are as follows:

1) Experimentally test the function of colour patterns in social status signalling. We will introduce size-matched individuals with different colourations to anemone hosts with breeding pairs and determine the level of aggression towards them. We predict that individuals with more developed colour patterns will receive more aggression from dominants, indicating social status signalling via colour patterns.

2) Experimentally test the function of colour patterns in individual recognition. We will introduce familiar and unfamiliar size-matched individuals to anemonefish groups, in a set-up that only allows transfer of visual cues, and determine level of aggression towards them. We predict that familiar individuals will receive less aggression from group members, indicating individual recognition via colour patterns.

3) Quantify the plasticity in colour pattern development in response to social context. Firstly, we will introduce settlers to anemone hosts as dominants or subordinates. We predict that subordinate settlers will develop colour patterns slower than dominant settlers to avoid aggression from dominants.

Secondly, we will remove individuals from anemonefish groups to allow ascension to dominant status and assess changes to colour patterns. We predict that individuals ascending status will show greater change in colour patterns compared to those not changing social status.

4) Quantify variation in social systems and colour patterns across the Amphiprion genus. Using three Amphiprion species (A. percula, A. perideraion and A. clarkii), we will photograph individuals and record behaviours in order to quantify colour pattern characteristics and social network matrices. We predict variation in social systems and colour patterns across species due to differences in ecology and phylogeny and that social systems and colour patterns will co-vary.

For example, species displaying hallmark patterns of status signalling and individual recognition will likely have more cooperation, less conflict.