The effects of mating probability on the population genetics of nematodes

We review how constraints on the mating probability of female worms by segr egation within individual host guts form a critical element in the parasite population structure of nematodes. We consider the effects of these constr aints on the population genetics of nematodes under various assumptions reg arding worm competition as reflected in the relationship between the abunda nce of a certain genotype within the gut and the probability of reproductiv e success. The consequences for the emergence of resistance to drugs and im munotherapy and implications for host-parasite coevolution are discussed. W e also review evidence for genetic heterogeneity in parasite populations as a necessary prerequisite for the applicability of mating probability model s designed to assess the population genetics of nematodes.