Cleaning is an often mutualistic behaviour among some marine species in which typically small and/or juvenile fishes (cleaners) locate and feed on ectoparasites off the bodies of larger taxa (clients). Some species obtain nearly all calories through cleaning while others use cleaning as a supplement.
In this study, researchers examined the evolutionary history of cleaning in five marine fish families in order to determine how and when this behaviour arose and whether the trait is restricted to species of a certain shape or size.
The authors found that cleaning evolved relatively recently with no one common ancestor in any family. By assigning species to distinct non-overlapping biogeographic regions using GBIF-mediated occurrences, they show that obligate cleaners in two families evolved in parallel and almost at same time in separate regions of the world: Labroides in the Indian Ocean and Elacatinus in the Western Atlantic.
By comparing photos of cleaner species with superimposed digitized body shape landmarks, they also showed that obligate cleaning is only present in elongate-bodied species with anterior pectoral fin attachment and eye positioning.