DEVELOPMENT OF ACCESSORY SEXUAL ORGANS IN BIOMPHALARIA-GLABRATA (PLANORBIDAE) IN RELATION TO TIMING OF INFECTION BY SCHISTOSOMA-MANSONI - CONSEQUENCES FOR ENERGY-UTILIZATION PATTERNS BY THE PARASITE

The growth rates of ovotestis and individual accessory sexual organs (ASO) of Biomphalaria glabrata snails were studied for controls and for immature and mature snails infected with Schistosoma mansoni. The infection of immature B. glabrata strongly delays growth of the ovotestis and inhibits the development of the accessory sexual organs. There is no significant difference up to 2 weeks post infection in the volume of the ovotestis and the ASO between mature infected B. glabrata and control snails. From 3 to 4 weeks post infection there was a reduction in the volume of the ovotestis and the ASO of infected mature B. glabrata; then growth of the ovotestis, albumen gland and female organs was stopped, but the effect of infection was less consistent for the male organs. For a parasite, immature and mature snails have to be considered as two different resource environments, each having at infection time a particular pattern of resource allocation, towards growth for juvenile and towards reproduction for adult snails, changing the possible energy utilization patterns which can be used by the trematode.