Résumé
We thank Ian Sutherland for his insightful comments. Dealing with surrogate measures of fecundity in gut parasites has always been problematic because there are variations in the daily production of eggs and in the relationship between worm numbers and egg output, and also variations from diverse host-specific effects. Thus, we have tended to standardize our measurements to eggs per gram (epg) to facilitate comparisons.In this study, it is indeed correct that fasting can decrease the quantity of feces produced. However, in these infected rats, the feces were collected continuously over 24 h and, while there was a small reduction in the fecal output from these fasted rats, the difference was not significant when compared with the controls (fed rats). Changes in fecal output after fasting are not immediate, presumably because dry matter might accumulate in the lower intestines. In our data, although there appeared to be a higher number of epg in the fasted rats, this was not a statistically significant difference. Thus, we simply concluded that the change in the egg development strategy by the worm was in response to host perturbation in order to maintain egg production at levels before fasting. We cannot argue that the strategy increased fecal contamination. This strategic response by the parasite is short term and it is not maintained beyond the first day. We have also infected rats that had been fasted for 48 hours with Hymenolepis diminuta (not reported in our article). In these animals, there was a significant reduction in fecal output and in the number of epg, and thus in total egg production. However, between 24 h and 48 h of fasting, these tapeworms began to de-strobilate (a clearly adaptive response to prolonged fasting), but this complicated our inferences on the egg-assembly strategy in these worms because many of the recovered worms had no strobilas. One could argue that producing eggs was unprofitable unless there were feces present to disperse the eggs. Again, this would support our contention that parasite strategies are state-dependent.