Body condition and reproductive capacity of three‐spined stickleback infected with the cestode Schistocephalus solidus

The relationship between reproductive ability and the residual index of body condition in three‐spined stickleback Gasterosteus aculeatus from a population infected with the cestode macroparasite Schistocephalus solidus in Walby Lake, Alaska, was examined. In general, reproductive activities resulted in significantly lower levels of body condition in three‐spined stickleback during the latter part of the breeding season, and relatively high levels of S. solidus infection intensified the energetic drain. Although female body condition did not differ significantly due just to the presence of S. solidus , increased parasite index did have a significant negative effect on female body condition. Males showed significantly lower levels of body condition in response to S. solidus infection alone and in association with a greater parasite index. Males had greater mean parasite indices than females. Females had significantly lower body condition than males, which may be due to discrepancies in energy expenditure between the sexes during reproduction. Females with greater body condition were significantly more likely to produce a clutch of eggs than those with lower condition, suggesting a threshold effect of body condition on reproductive capacity.