Gametocyte Maturation,Exflagellation and Fertilization in Parahaemoproteus (=Haemoproteus) velans (Coatney & Roudabush) (Haemosporidia: Haemoproteidae): an Ultrastructural Study*

SYNOPSIS. The structural changes in macro and microgametocytes of Parahaemoproteus velans following removal of infected blood from the avian host were studied in the light and electron microscope. Gametocytes of both sexes round up and soon escape from their host cells. Shortly thereafter they assume a dumbbell shape. The microgametocyte undergoes exflagellation forming 8 slender microgametes. During fertilization the entire microgamete appears to enter the female. The most striking ultrastructural change in the formation of the macrogamete is the condensation and enclosure by a membrane of abundant amophorus dense material seen in the cytoplasm of the immature gametocyte. Maturation of the microgametocyte begins prior to its escape from the host cell. Axonemes are present in the cytoplasm and nuclear reorganization occurs while the parasite is intracellular. Bundles of microtubules associated with condensed chromatin are found in the peripheral cytoplasm of maturing forms and apparently participate in the formation of small compact microgamete nuclei. Each of these filiform structures consists of a dense, centrally located nucleus and a single axoneme lying in flocculent cytoplasm. The nucleus and axoneme of the microgamete are seen free in the cytoplasm of a fertilized macrogamete.     

Gametogenesis, fertilization and ookinete differentiation of Leucocytozoon smithi

Development of Leucocytozoon smithi during gametogenesis, fertilization, and ookinete differentiation was studied by light and electron microscopy. Gametogenesis occurred rapidly, within 1-2 min after gametocytes were ingested by black flies. Usually one axoneme, but not infrequently two, was observed in microgametes. The macrogamete nucleus was characteristically elongated and fragmented, with a convoluted nuclear envelope. Fertilization occurred within five min after ingestion of gametocytes by the vector. The entire axoneme and nucleus of the microgamete entered the cytoplasm of the macrogamete. Zygote differentiation resembled sporozoite formation in that a thickened inner membrane and subpellicular microtubules developed beneath the plasmalemma, followed by cytoplasmic protrusion or evagination to form the anterior end. Extension of the inner thickened membrane continued as the zygote elongated. Development of sausage-shaped ookinetes was completed within 6-8 h after ingestion of a blood meal by a black fly. Mature ookinetes possessed a single nucleus, double-layered pellicle, canopy, apical pore, polar ring complex, subpellicular microtubules, micronemes, crystalloids, abundant mitochondria, endoplasmic reticulum, and ribosomes. Comparison of development of L. smithi with species of Plasmodium and Haemoproteus revealed general similarities in both sexual and asexual development within the insect vector. A diagram summarizing life cycle events for L. smithi is included.