Evidence for diploidy in metacyclic forms of African trypanosomes

The DNA contents of bloodstream form trypanosomes (life cycle stages circulating in the blood of the vertebrate host) of four African Trypanosoma species and of metacyclic forms (the life cycle stage that is injected into the vertebrate by the tsetse fly during its bite) of the same four species were measured by cytofluorometry of individual cells or nuclei. The results showed unambiguously that the metacyclic forms cannot be considered to be products of meiosis containing only half of the DNA of bloodstream forms, in contrast to what was previously reported for Trypanosoma brucei [Zampetti-Bosseler, F., Schweizer, J., Pays, E., Jenni, L. & Steinert, M. (1986) Proc. Natl. Acad. Sci. USA 83, 6063-6064] during an attempt to localize the gametes in the life cycle after experimental evidence of sexual gene exchange in this parasite was reported.