Abstract
Allelic frequency variation at the malate dehydrogenase (E.C.1.1.1.37) polymorphic locus (Mdh-1) was analysed during several successive generations in four strains of Schistosoma mansoni from Guadeloupe, maintained experimentally on mice. A rapid evolution of the frequency of the Mdh-1a allele is interpreted as being the result of an interaction between experimental drift and selection induced by the murine laboratory host. These experimental results are compared to the genetic structures observed among the corresponding natural populations of S. mansoni in Guadeloupe (West Indies). They strengthen the hypothesis of a natural host-induced selection by the murine host (Rattus rattus), which, in Guadeloupe, plays the role of host reservoir for this human schistosome.