In vitro development of Haemoproteus parasites: the efficiency of reproductive cells increase during simultaneous sexual process of different lineages.

Recent in vitro experimental studies reported the complex patterns of haemosporidian (Haemosporida) between-lineage interactions, which prevent mixing of lineages during simultaneous sexual process. Numerous anomalous ookinetes have been observed; these are not involved in sporogony. Massive development of such ookinetes might influence parasite transmission but is insufficiently investigated. The simultaneous sexual process of several lineages is a common phenomenon in vectors due to high prevalence of haemosporidian co-infections in wildlife. It remains unclear if the number of anomalous ookinetes changes during dual-infection sporogony in comparison with the single-infection process. We calculated proportions of the anomalous and normal ookinetes, which developed during single-infection (control) and dual-infection experiments in vitro conditions. Three mitochondrial cytochrome b lineages belonging to three Haemoproteus spp. (Haemosporida, Haemoproteidae) were isolated from naturally infected passerine birds. Sexual process and ookinete development were initiated in vitro by mixing blood containing mature gametocytes of two different parasites; the following experiments were performed: (1) Haemoproteus tartakovskyi (lineage hSISKIN1) × Haemoproteus lanii (lineage hRBS4) and (2) Haemoproteus belopolskyi (hHIICT3) × H. lanii (hRBS4). Genetic difference between lineages was 5.0-5.9%. Normal and anomalous ookinetes developed in all control and dual-infection experiments. The number of anomalous ookinetes markedly decreased, and normal ookinetes increased in all dual-infection experiments in comparison with those in controls, except for H. belopolskyi, in which proportion of the anomalous and normal ookinetes did not change. This study shows that simultaneous sexual process of two genetically distant lineages of haemosporidian parasites might increase the efficiency of reproductive cells, resulting in the development of a greater number of normal ookinetes. The marked increase of the number of normal ookinetes, which is involved in sporogony, indicates the success of sporogony in dual infections. Some haemosporidian lineages might benefit from simultaneous sporogony. Widespread avian Haemoproteus spp. are convenient and laboratory-friendly organisms for in vitro experimental research addressing between-lineage interaction in parasites during the sexual process.