Commitment to sexual differentiation in the human malaria parasite, Plasmodium falciparum

a1 Institute of Cell, Animal and Population Biology, University of Edinburgh, King's Buildings, West Mains Road, Edinburgh, Scotland EH9 3JT


The differentiation of the two sexes in the gametocytogenesis of Plasmodium falciparum was investigated using a plaque assay and antibodies specific for various stages and sexes of gametocytes. Immunofluorescence assays on plaques of cultured parasites grown in monolayers of erythrocytes revealed that the merozoites released from a single sexually-committed schizont became either all male or all female gametocytes. Thus, the commitment of this species to differentiate into one sex or the other is likely to occur prior to the nuclear division of the sexually-committed schizont. The characteristic female-biased gametocyte sex ratio observed for many Plasmodium species is manifested in P. falciparum by a greater percentage of schizonts that produce female gametocytes (67–71%) than those that yield males. From the plaque assay, it was determined that the number of gametocytes produced per sexually-committed schizont was similar for both sexes, indicating that allocation of parasite resources was equal for each sex of gametocyte. The timing of sexual differentiation and features of the gametocyte sex ratio is discussed in relation to previous observations on P. falciparum and related malaria parasites.

(Received November 5 1999)
(Revised February 18 2000)
(Accepted February 18 2000)

Key Words: gametocytogenesis; malaria; plaque assay; Plasmodium falciparum; sex differentiation; sex ratio.

c1 Corresponding author now at: Division of Infection and Immunity, Institute of Biomedical and Life Sciences, University of Glasgow, Joseph Black Building, Glasgow G12 8QQ, Scotland, UK. Tel: +44 141 330 4235. Fax: +44 141 330 4600. E-mail
p1 Current address: Clinical Sciences Division, University of Toronto, Medical Sciences Building, 1 King's College Circle, Toronto M5S 1A5, Ontario, Canada.