Epidermal club cells do not protect fathead minnows against trematode cercariae: a test of the anti‐parasite hypothesis

Epidermal club cells of fishes in the superorder ostariophysi have puzzled evolutionary biologists because they were historically linked to chemical alarm signalling and relied on group selectionist explanations. Alternative hypotheses to explain the existence of these cells include the possibility of an anti‐pathogenic or anti‐parasitic function. If this is so, individual fish should invest in increased numbers of club cells after exposure to parasites, and club cells should contain components that reduce the infectivity of skin‐penetrating larvae. Infectivity of cercariae of the trematode Ornithodiplostomum sp. was significantly reduced when exposed to the skin extract of fathead minnows (an ostariophysan), but also to skin extract of mollies (a non‐ostariophysan that lacks club cells), respectively, compared to controls. Moreover, club cell density was not affected by exposure to cercariae. Taken together, these results are inconsistent with an anti‐parasite function for these cells and instead suggest a generic role in response to injury. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 884–890.