AGE SIZE-SPECIFIC AND TIME-SPECIFIC EFFECTS OF SCHISTOSOMA-MANSONI ONENERGY ALLOCATION PATTERNS OF ITS SNAIL HOST BIOMPHALARIA-GLABRATA/

Snail hosts of different ages constitute different resource environmen ts for larval trematodes because each individual has a particular ener gy budget and energy allocation pattern at the time of infection. Effe cts of monomiracidial trematode infections on shell growth, body dry w eight and reproductive effort of the snail host were compared between controls and infected juvenile and adult snails during the prepatent a nd patent periods. The results demonstrate phenotypic plasticity in th e host response. There is an age/size-specific effect characterized by limitation of growth rate when snails are infected as juveniles and r eduction of reproductive effort when snails are infected as adults, an d a time-specific effect with early enhancement of growth rate and rep roductive effort for infected juvenile and adult snails respectively d uring prepatency, before reduction and cessation during patency. The p arasite is considered as a generalist in its energy exploitation strat egy of the snail host, but taking into account the differential host r esponses observed relative to the host age, the possibility of a host preference for juvenile or adult snails is discussed.