Cheney, KL, Grutter, AS, Marshall, NJ. (2008) Facultative mimicry: cues for colour change and colour accuracy in a coral reef fish. Proceedings of the Royal Society: Biological Sciences.275:117-122.
Cheney et al (2008) studied the rare phenomenon of facultative mimicry in the coral reef fish Plagiotremus rhinorhynchos (bluestriped fangblenny). Facultative mimicry occurs when an organism can switch on or change mimic coloration at will to avoid predators or help it to catch prey. To date only two known species posses this ability, one an invertebrate the 'mimic octopus' Thaumoctopus mimicus and the other, the focus of this study, the bluestriped fangblenny. The fangblenny changes its color in the presence of its model, a juvenile cleaner fish of the species Labroides dimidiatus. Once the color change has taken effect the fangblenny attacks client fish and removes scales and dermal tissue from its victims. The fangblenny is also reported to change its color apparently to hide in schools of heterospecifics. The authors were interested in what species of fish the fangblenny will mimic, the relative abundance of the mimetic form in the field and the spectral accuracy of mimic coloration achieved by the fangblenny. It was found that the fangblenny in captivity only mimicked the coloration of the cleaner model, not another cleaner species or a schooling fish. The lack of color change in the presence of schooling fish was unexpected and the authors attributed this result to stress or the fact that the schooling fish were not native to the fangblenny's natural habitat and therefore may not have solicited a mimetic response. In concurrence with the authors predictions mimic fangblennies were more prevalent in areas where there were more juvenile cleaner fish present. Finally, and most relevant to our discussions were the measurements of the accuracy of the fangblenny coloration compared to their supposed models. The authors found that the spectral reflectance of both the body color and striping of the fangblenny nearly perfectly matched that of its juvenile cleaner model. When compared to some of its heterospecific schooling cohorts the match of the spectra was less perfect although similar.
This study, especially the last portion, highlights the relevance to lecture as well as the general importance of taking subjective spectral measurements when assessing coloration of animals. Of particular interest is one mimic/model spectra comparison that revealed the model had components of its color that were in the UV range while the mimic lacked that short of a wavelength component in its spectra. The authors speculated that such a difference could contribute to increased detectability of the mimic in shoals of this particular model, but this would depend on the ability of other fish to perceive light in the UV spectrum, a topic which the authors intended to study in future work.