Influence of mating on surface nutrient exchange in schistosomes

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Abstract
In schistosomes, the mating process influences male-female transfer and gender-specific exchange of nutrients. The paired male schistosome provides glucose to the female partner. Male-to-female intertegumental transfer of^14C-labeled glucose,^14C-labeled 3- O -methylglucose, [^14C]2-deoxyglucose and 2-fluorodeoxyglucose has been demonstrated in schistosomes. This phenomenon has been studied extensively in Schistosoma mansoni , and confirmed in Schistosoma japonicum , as well as S. haematobium , using radioactive pulsing methods. Male schistosomes contain significantly greater quantities (nmol/mg worm water) of glucose than do females. The transfer of glucose is apparently not an energy-dependent process, but occurs along this concentration gradient. Most, if not all, of the glucose utilized by the female is transferred from the male partner via tegumentary-facilitated diffusion mechanisms, free diffusion, or some combination of these two components. Unpaired male schistosomes contain greater quantities of glycogen than do comparable paired schistosomes, indicating that the presence of a female in the gynecophoral canal depletes the reserves of the male partner; this is additional indirect evidence for male-to-female transfer of glucose. Tegumentary surface uptake of acidic amino acids has been compared in paired and separated male and female schistosomes. In S. mansoni , a saturable carrier-mediated mechanism has been defined which operates only in unpaired male and unpaired female teguments. In contrast, the uptake of aspartate and glutamate is not seen in paired worms of this species. Tegumental uptake of acidic amino acids is not observed in paired or unpaired male or female S. japonicum . However, in S. haematobium , significant quantities of aspartate are taken up by both paired and unpaired male schistosomes. Measurable aspartate uptake is seen in paired female S. haematobium , but in the separated female, there is minimal uptake of this acidic amino acid. Thus the permeability of the teguments of human schistosome species to acidic amino acids is modified in response to the paired state in S. mansoni and S. haematobium , but these characteristics are not shared by S. japonicum .