Parasite infection rather than tactile stimulation is the proximate cause of cleaning behaviour in reef fish

Cleaning behavior is a popular example of non-kin cooperation. However, qua ntitative support for this is generally sparse and the alternative, that cl eaners are parasitic: has also been proposed. Although the behaviour involv es some of the most complex and highly developed interspecific communicatio n signals known, the proximate causal factors for why clients Seek cleaners are controversial. However, this information is essential to understanding the evolution of cleaning. I tested whether clients seek cleaners in respo nse to parasite infection or whether clients seek cleaners for tactile stim ulation regardless of parasite load. Parasite loads oil client fish were ma nipulated and clients exposed to cleaner fish and control fish hehind glass . I found that parasitized client fish spent more time than unparasitized f ish next to a cleaner fish. In addition; parasitized clients spent more rim e next to cleaners than next to control fish whereas unparasitized fish wer e not attracted to cleaners. This study shows, I believe for the first time , which is somewhat surprising, that parasite infection alone causes client s to seek cleaning by cleaners and provides insight into how this behaviour evolved.