Cleaning up the biogeography of Labroides dimidiatus using phylogenetics and morphometrics

Cleaner fishes are some of the most conspicuous organisms on coral reefs due to their behaviour and prominent body pattern, consisting of a lateral stripe and blue/yellow colouration. All obligate cleaner fishes share this body stripe pattern, which is an important signal for attracting client fishes. However, variability in the cleaning signal of the cleaner fish Labroides dimidiatus has been documented across its range. Here, we investigate the geographic distribution of cleaner signal polymorphisms in L. dimidiatus and contrast this to phylogeographic variation in mitochondrial (mt) DNA. We used samples from 12 sites for genetic analyses, encompassing much of L. dimidiatus' range from the Red Sea to Fiji. We obtained morphometric measures of the cleaner signal body stripe width from individuals among six of the sites and qualitatively grouped tail stripe shape. mtDNA control region sequences were used for phylogenetic and population genetic analyses. We found that body stripe width was significantly correlated with tail stripe shape and geographical location, with Indian Ocean populations differing in morphology from western Pacific populations. L. dimidiatus haplotypes formed two reciprocally monophyletic clades, although in contrast to morphology, Japanese cleaner fish fell within the same clade as Indian Ocean cleaner fish and both clade types were sympatric in Papua New Guinea. An additional novel finding of our research was that the inclusion of two closely related cleaner fish species, Labroides pectoralis and Labroides bicolor, in the phylogenetic analysis rendered L. dimidiatus polyphyletic. Overall, the findings suggest the diversity within L. dimidiatus is underestimated.