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SummaryProterometra macrostoma and P. edneyi infect the same snail host, Goniobasis semicarinata, but different fish hosts in their life-cycles. Cercariae of P. macrostoma complete development in sunfish, those of P. edneyi in darters; fish become infected when they ingest free-swimming cercariae as ‘prey’. Laboratory and field experiments were designed to test the hypothesis that light: dark (L: D) cycling regulates emergence of both species. Under L: D cycling conditions, P. macrostoma emerged in the dark and P. edneyi in the light. These emergence patterns resulted from differential sensitivity to light and dark. In the laboratory and field, reversing the light and dark periods resulted in corresponding alterations in emergence patterns of both species. Both species emerged in constant light and constant dark, but their emergence patterns were altered. Emergence patterns may represent adaptations that make the cercariae more susceptible to ‘predation’ by their respective fish hosts.

The absorption kinetics of some 14-C-labeled simple sugards in adults of Schistosoma mansoni are described. The influx of fructose and 3-0-methylglucose was by diffusion alone, while glucose, 2-deoxyglucose (2DOG), galactose, glucosamine, and mannose were absorbed by mediated transport as well as by diffusion. Although absorbed glucose was rapidly metabolized, uptake rates of radio-glucose in 2-min incubations corresponded with the amount of glucose (determined chemically) removed from the incubation medium. In 30-min incubations 2DOG was slowly metabolized and accumulated against an apparent concentration difference. The mediated transport of glucose and 2DOG was inhibited in Na+-free media, and by the presence of ouabain, phlorizin, phloretin, and other sugars. Accordingly, influxes of glucose of 2DOG and 22-Na+ were coupled. On a per mg protein basis, female worms transported more 2DOG and glucose, but less glycine, than did males. However, the rate of glucose metabolism by male and female worms incubated together was greater than that of either males or females incubated separately. The nature of sugar transport in schistosomes and other flatworms is similar to that in vertebrates.

Monosaccharide transport systems were identified in rediae and cercariae of Proterometra macrostoma. Glucose transport by cercariae in vitro was accomplished by the bodies, but tails absorbed glucose by diffusion alone. No sugar transport system was detected in adults obtained from laboratory infections of sunfish. Temperature of Elkhorn Creek where infected snails (Goniobasis livescens) were found varies from 28 C in summer to 5 C in winter. Glucose transport by both larval stages was optimal between 30 and 25 C and was negligible below 15 C. Transport by rediae was activated by Na+ and was maximal at 50 mM, the approximate Na+ concentration of snail hemolymph. The redial glucose transport system was inhibited by various sugars and was more sensitive to phlorizin than to phloretin. Rediae accumulated glucose and nonmetabolized 3-O-methyl-glucose against apparent concentration gradients, indicating an active transport system. In contrast, glucose transport by "embryonic" cercariae was completely inhibited by 10 mM Na+. Transport by cercariae aged in creek, water 6 hr became relatively insensitive to Na+, and were less permeable to glucose by diffusion. The cercarial system differed in other characteristics from the redial system, including its high sensitivity to phloretin relative to phlorizin and its lower Vmax. The cercarial system apparently functioned only as a facilitated diffusion system that served to move sugar across the tegument down its chemical gradient. Development of P. macrostoma thus showed functional transformations of the tegument that may be subject to regulation by environmental factors.