HOW DO PARASITES COST THEIR HOSTS - PRELIMINARY ANSWERS FROM TREMATODES AND DAPHNIA-OBTUSA

Cladocerans (Daphnia obtusa) in seasonal ponds in southeast Texas are infected with a trematode parasite (n. sp.). Infestation rate varies c onsiderably among ponds and years, and among ponds within years. The p arasite is rare in individuals < 1.00 mm long but is common in individ uals 1,25-1.75 mm long. The parasite has no effect on whether females become gravid. Although there is a significant correlation between len gth and egg production for unparasitized females, this is not the case for parasitized individuals. An infection of 1-2 parasites does not a ffect fecundity; however, greater infections are correlated with reduc ed egg production. Another cost to Daphnia of harboring the parasite i s reduced survivorship, particularly among larger individuals. As thes e individuals have the capacity to produce more eggs than smaller indi viduals, it is likely that the parasite also causes a reduction in lif etime reproduction in addition to that in any one reproductive episode .