A Theory and some empirics on modern maritime piracy

Abstract

Parasites take their resources from hosts and thus directly reduceavailable resources for hosts' own body functions, such as growth andreproduction. Furthermore, parasite infections cause significantindirect costs to their hosts in terms of increased investments onimmune defense. In this study, we investigated the impact of parasiteinfection on the sperm quality and expression of secondary sexualornamentation (saturation of the red abdominal colouration and number ofbreeding tubercles) in the Eurasian minnow (Phoxinus phoxinus). Weexposed minnows to a high and low dose of common nonspecific fishectoparasite, the glochidia larvae of duck mussel (Anodonta anatina) andtested whether parasite infection leads to trade-off in sperm qualityand/or ornamental expression. We found that glochidia infection reducesthe curvature of the sperm swimming trajectory, number of breedingtubercles, and possibly male competitive ability, but does not affectexpression of male color ornamentation. Furthermore, glochidia infectionwas found to reduce sperm motility, but only when all the noninfectedindividuals were excluded from the model. Supporting one of thepredictions by phenotype-linked fertility hypothesis both inhigh-infection and low-infection group male breeding colouration waspositively associated with sperm quality. Our results suggest thatalthough glochidia infection may have negative impact on malereproductive success, parasite-induced costs may not create strongtrade-off between breeding colouration and sperm quality or that suchtrade-off become detectable only in resource-limited conditions.