Evidence for haploidy in metacyclic forms of Trypanosoma brucei.

The parasitic flagellate Trypanosoma brucei undergoes a series of morphologic and metabolic changes during its passage in the digestive organs of its insect vector, a Glossina or tsetse fly. This morphogenesis ends by the differentiation, in the salivary gland of the fly, of the metacyclic form, which will be transmitted in the bloodstream of the mammalian host. On the basis of DNA microfluorometric measurements, we propose that these metacyclic trypanosomes have a haploid amount of DNA, compared to that of bloodstream forms and also of the proventricular forms, which initiate the invasion of the salivary glands. It can be inferred that trypanosomes undergo meiosis during their developmental cycle in the tsetse fly's salivary glands and syngamy shortly after cyclic transmission.