Regulation, constraints and benefits of colour plasticity in a mimicry system

Abstract

Rapid colour change is used in aggressive interactions, ontogenetic transitions, nuptial displays and to prevent detection and/or recognition from predators or prey. The underlying mechanisms, constraints and benefits of colour change are often unclear, but examining such factors offers insights into phenotypic plasticity. Here, we investigated the mechanisms behind how an aggressive reef fish mimic (bluestriped fangblenny Plagiotremus rhinorhynchos) changes colour rapidly (1-5 min) between mimetic and other colour forms. Black with one neon blue dorsal stripe (mimic), black with two neon blue stripes, brown, olive and orange forms differed in melanophore density. Fish skin biopsies were modulated in vitro by hormones, and smaller fangblennies changed coloration more rapidly than larger fish suggesting that the ability to change colour is diminished as fish get larger. Individuals may be limited by differences in pigment cell densities to change colour between extreme colour forms (black to orange); therefore, longer morphological changes may also occur or fangblennies may exhibit dimorphic populations. Behavioural observations suggest that small black and orange individuals were equally successful in attacking passing fish to feed on dermal tissue/scales, indicating that deceptive strategies used by each colour form may deliver equal fitness benefits. The present study demonstrates for the first time how fangblennies change colour and highlights that colour plasticity offers important adaptive advantage; however, physiological constraints should also be considered.