Individual recognition in anemonefishes — causes and consequences of interspecific variation

Individual recognition, the ability to remember and recognize individuals, is an important skill for many animals, whether they live in complex groups with division of labor or live solitarily but need to recognize mating partners (Tibbetts & Dale 2007). Understanding if and how individuals recognize each other can illuminate fundamental principles of behaviour and social organisation. In social species, distinctive phenotypes that signal identity, such as color patterns, may be expected because they can help reduce conflict (Tibbetts et al. 2017). Studying individual recognition often involves manipulating these signals of identity and measuring behaviours. More recently, social network analysis is emerging as a potential useful tool to reveal how individual recognition may differ across species and populations. Network analysis allows for the quantification of social characteristics such as non-random clustering and between-individual variation in social position. This in turn allows for the identification of differences in social structure between species that may be associated with differing levels of complexity in individual recognition (Gokcekus et al. 2021). This PhD project will use a combined approach of behavioural studies, in-situ experiments, studying color patterns variation and social network analysis to understand differences in individual recognition among closely related species.

Anemonefishes of the genus Amphiprion all share the same basic social structure; a group of 2-12 individuals occupies an anemone host, there is a strict size hierarchy within each group, with the largest individual being the female, the second largest the male and all other group members progressively smaller and non-breeders. These complex groups, where some individuals reproduce and others don’t, have become a model system to understand social evolution in the marine environment (reviewed in Rueger et al. 2021). However, most of our work thus far has focused on understanding the basic social structures that all anemonefishes have in common and has been based on few model species (e.g., Buston 2003). Understanding why we see differences in social structure between the 28 closely related species of anemonefish will help us illuminate the role of individual recognition in animal social systems.

The goals of this PhD project are to understand how anemonefishes differ in their capacity to recognize individuals, whether this recognition is based on the difference in color pattern and what the causes and consequences of these differences are in terms of the fishes’ social structures. Does the capacity for individual recognition influence social structure? Or do different social structures influence benefits of identity signaling and thereby colour patterns? Using an interspecific comparative approach will help illuminate the directionality of these relationships. The specific objectives of the project are:

Objective 1— Quantify variation in social system and color pattern across the Amphiprion genus.

Hypothesis 1: Social systems differ among the 28 species of Amphiprion due to variation in ecology and phylogeny. We predict that some species will have social structures with more intergroup movement, more conflict and less cooperation than others.

Hypothesis 2: Color patterns in Amphiprion vary due to variation in ecology and phylogeny. We predict that some colour patterns will show the hallmarks of individual recognition patterns, e.g., variability and polymodal frequency distribution, and others will not.

Hypothesis 3. Social systems and colour pattern co-vary. We predict that individual recognition signals will be associated with social structures where there is less movement, less conflict and more cooperation.

Objective 2— Experimentally test if individual recognition in Amphiprion relies on color patterns and if recognition varies between species.

Hypothesis 1: Within species individuals are more tolerant of familiar than unfamiliar individuals. We predict that when individuals’ color patterns are altered, other group members will show more aggressive behaviours towards them.

Hypothesis 2: Among species individuals will be less tolerant of unfamiliar individuals than familiar individuals when there is less movement, less conflict, more cooperation and individuals are more recognizable. We predict that social network analysis will show differences in social structure between species that may be associated with differing levels of complexity in individual recognition, such as non-random clustering.

For this objective we propose to use three species of anemonefish that represent the range of different social systems and color patterns present in the genus Amphiprion: 1) A. percula, which is the most well studied species and the most site attached and peaceful (Buston 2003, Rueger et al. 2021a). 2) A. perideraion, which has been shown to be more aggressive than A. percula, and to display fewer helping behaviours. 3) A. clarkii, which is the most generalist species, found associated with all 10 species of sea anemone that host anemonefishes. It is larger than the other two species and is known to move further from its anemone host, even capable of changing anemones and social groups (Hattori 2002, Cleveland et al. 2011). We predict that the differences in behaviour between the three species are connected to a difference in how well group members can recognize individual conspecifics.

Theresa Rueger at Newcastle University will be the primary supervisor and provide training in field techniques, statistical modelling and academic writing. The project will be co-supervised by Michael Webster at St Andrews, who has wide-ranging expertise in social behaviour studies, particularly in fishes. Peter Buston at Boston University (USA), an expert on anemonefishes, and Elizabeth Tibbetts at University of Michigan (USA), an expert on individual recognition, will be collaborators on the project and support training in color pattern quantification.

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Image Captions

Kimbe Bay, Papua New Guinea,Clown anemonefish, Amphiprion percula, in their host anemone, Heteractis magnifica


To address the two objectives, the project will include literature review, behavioural assays, social network analysis, in-situ experiments and quantification of colour pattern variation.

Field work will take place on SCUBA at Mahonia Na Dari research and conservation center in Kimbe Bay, Papua New Guinea. We have large, well-known and easily accessible populations of anemonefishes at this site.

Behaviours and social networks will be assessed by recording videos of the fishes’ behaviour in the wild. Social network analysis and statistical modelling will allow for detailed comparisons between species. Quantifying diverse types of interactions among individuals, including cooperation and conflict, will allow for the illumination of social structures which, in turn, provides insights into individual behaviours.

The link between social recognition and behaviour/social structure will be further explored using in-situ experiments where identity signals, such as colour pattern, will be manipulated and the effect on behaviour and social organization will be observed (Fricke 1973, Tibbetts 2002).

Colour pattern variation, a likely candidate for identity signal in anemonefishes, will be quantified for the different species of anemonefish across the phylogeny (Dale 2000, 2001) and it will be explored whether there is an association with the social system (Tibbetts 2004). Split beam photography will be used to record colour patterns in visible as well as UV spectra, since recent studies have shown that anemonefishes can see in UV (Mitchell et al. 2021), and some of their markings reflect UV, which might have an important role in social organization (Mitchell et al. 2022).

Project Timeline

Year 1

• Comprehensive literature review of individual recognition and size-based hierarchies.
• Preparation of first manuscript.
• Training in tropical marine field methods and techniques during field season 1.
• Video recordings of behaviour of three species.

Year 2

• Video analysis.
• Training in social network analysis and other relevant analytical skills.
• Preparation of second manuscript.
• Field experiments to test if individual recognition explains differences during field season 2.
• Social network analysis, statistical analysis.

Year 3

• Preparation of third manuscript.
• Development of quantification method for variation in color patterns.
• Score color pattern variation across phylogeny and look at connection to variation in social system.

Year 3.5

• Preparation of fourth manuscript.
• Thesis completion.

& Skills

The student will be trained in tropical marine field methods such as locating, tagging, catching and measuring anemonefishes, how to handle gear and safely conduct research underwater. The student will also be trained in behavioural studies, including how to obtain and analyse videos of fish behaviour and how to design and conduct in-situ experiments. Analytical training will include social network analysis and statistical modelling implemented in R. In addition, Newcastle University offers post-graduate workshops such as ‘Statistical modelling with R’ and ‘Introduction to data management’. Scientific writing, giving oral presentations and peer mentoring will also be part of the training. Travel to international conferences to present project results will be encouraged.

While in the field in Papua New Guinea, the student will have the opportunity to help facilitate Mahonia Na Dari’s MEEP (marine and environmental education program) with local school children. Activities usually include snorkeling tours, mangrove planting or fish dissections as well as seminars. This will hone teaching and outreach skills crucial for a successful scientific career and crucial to understand our responsibility as scientists to respect and support the communities who give us access to their reefs.

References & further reading

Buston, P. (2003). Size and growth modification in clownfish. Nature, 424(6945), 145-146.

Cleveland, A., Verde, E. A., & Lee, R. W. (2011). Nutritional exchange in a tropical tripartite symbiosis: direct evidence for the transfer of nutrients from anemonefish to host anemone and zooxanthellae. Marine Biology, 158(3), 589-602.

Dale, J. (2000). Ornamental plumage does not signal male quality in red-billed queleas. Proceedings of the Royal Society of London. Series B: Biological Sciences, 267(1458), 2143-2149.

Dale, J., Lank, D. B., & Reeve, H. K. (2001). Signaling individual identity versus quality: a model and case studies with ruffs, queleas, and house finches. The American Naturalist, 158(1), 75-86.

Fricke, H. W. (1973). Individual partner recognition in fish. Field studies on Amphiprion bicinctus. Naturwissenschaften, 60(4), 204-205.

Gokcekus, S., Firth, J. A., Regan, C., & Sheldon, B. C. (2021). Recognising the key role of individual recognition in social networks. Trends in Ecology & Evolution, 36(11), 1024-1035.

Hattori, A. (2002). Small and large anemonefishes can coexist using the same patchy resources on a coral reef, before habitat destruction. Journal of Animal Ecology, 71(5), 824-831.

Mitchell, L. J., Cheney, K. L., Lührmann, M., Marshall, J., Michie, K., & Cortesi, F. (2021). Molecular evolution of ultraviolet visual opsins and spectral tuning of photoreceptors in anemonefishes (Amphiprioninae). Genome biology and evolution, 13(10), evab184.

Rueger, T., Barbasch, T. A., Wong, M. Y., Srinivasan, M., Jones, G. P., & Buston, P. M. (2018). Reproductive control via the threat of eviction in the clown anemonefish. Proceedings of the Royal, Society B, 285(1891), 20181295.

Rueger, T., Branconi, R., Froehlich, C. Y., Heatwole, S. J., Wong, M. Y., & Buston, P. M. (2021a). The next frontier in understanding the evolution of coral reef fish societies. Frontiers in Marine Science, 8, 665780

Rueger, T., Heatwole, S., & Wong, M. Y. (2021b). Cooperative and aggressive behaviours vary between ranks in anemonefish social hierarchies. bioRxiv: https://doi.org/10.1101/2021.01.19.427348

Tibbetts, E. A. (2002). Visual signals of individual identity in the wasp Polistes fuscatus. Proceedings of the Royal Society of London. Series B: Biological Sciences, 269(1499), 1423-1428.

Tibbetts, E. A. (2004). Complex social behaviour can select for variability in visual features: a case study in Polistes wasps. Proceedings of the Royal Society of London. Series B: Biological Sciences, 271(1551), 1955-1960.

Tibbetts, E. A., & Dale, J. (2007). Individual recognition: it is good to be different. Trends in ecology & evolution, 22(10), 529-537.

Tibbetts, E. A., Mullen, S. P., & Dale, J. (2017). Signal function drives phenotypic and genetic diversity: the effects of signalling individual identity, quality or behavioural strategy. Philosophical Transactions of the Royal Society B: Biological Sciences, 372(1724), 20160347.

Further information about the partner organization:

Mahonia Na Dari’s website: https://www.mndpng.org

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