Colour patterns influence symbiosis and competition in the anemonefish-host anemone symbiosis system

Counting Nemo: anemonefish Amphiprion ocellaris identify species by number of white bars

The brilliant colors of coral reef fish have received much research attention. This is well exemplified by anemonefish, which have distinct white bar patterns and inhabit host anemones and defend them as a territory. The 28 described species have between 0 and 3 white bars present, which has been suggested to be important for species recognition. In the present study, we found that Amphiprion ocellaris (a species that displays three white bars) hatched and reared in aquaria, when faced with an intruder fish, attacked their own species more frequently than other species of intruding anemonefish. Additionally, we explicitly tested whether this species could distinguish models with different numbers of bars. For this, 120 individuals of A. ocellaris were presented with four different models (no bars, and 1, 2 and 3 bars) and we compared whether the frequency of aggressive behavior towards the model differed according to the number of bars. The frequency of aggressive behavior toward the 3-bar model was the same as against living A. ocellaris, and was higher than towards any of the other models. We conclude that A. ocellaris use the number of white bars as a cue to identify and attack only competitors that might use the same host. We considered this as an important behavior for efficient host defense.

Anemonefishes: A model system for evolutionary genomics

Anemonefishes are an iconic group of coral reef fish particularly known for their mutualistic relationship with sea anemones. This mutualism is especially intriguing as it likely prompted the rapid diversification of anemonefish. Understanding the genomic architecture underlying this process has indeed become one of the holy grails of evolutionary research in these fishes. Recently, anemonefishes have also been used as a model system to study the molecular basis of highly complex traits such as color patterning, social sex change, larval dispersal and life span. Extensive genomic resources including several high-quality reference genomes, a linkage map, and various genetic tools have indeed enabled the identification of genomic features controlling some of these fascinating attributes, but also provided insights into the molecular mechanisms underlying adaptive responses to changing environments. Here, we review the latest findings and new avenues of research that have led to this group of fish being regarded as a model for evolutionary genomics.