Authors

T Anderson¹;  ¹ Texas Biomedical Research Institute, United States

Discussion

Malaria parasites are hermaphrodite, producing both male and female gametes, so they can either self-fertilize or outcross, yet the fitness consequences of selfing versus outcrossing remain poorly understood. Malaria parasite genetic crosses conducted in the laboratory are expected to result in both self-fertilization and outcrossing: yet a surprising excess of outcrossed progeny are frequently recovered from the vertebrate host in these crosses. This project was designed to investigated gamete fusion dynamics within mosquitoes and to compare the fitness of selfed and outcrossed zygotes. We generated florescent-labelled clones of NF54 (mCherry; African), and NHP4026 (GFP; Thai), crossed these parasites, and genotyped 8540 oocysts from 435 mosquitoes collected 7-14 days post-infection. Selfed NF54 oocysts are red, selfed NHP4026 oocysts are green, and outcrossed oocysts are orange. In two independent crosses, we observed decreasing proportions of outcrossed oocysts and increasing proportions of selfed oocysts over time. This pattern is consistent with the faster maturation of outcrossed oocysts compared with selfed oocysts. Our results suggest a substantial fitness advantage of outcrossing, potentially due to removal of deleterious mutations accumulated during asexual replication in the vertebrate host. We also found that oocyst genotype influenced oocyst size: selfed NF54 oocysts were larger than selfed NHP4026 oocysts, which may influence sporozoite production and transmission potential. Fluorescent labelled parasites provide clear resolution of mating patterns, temporal dynamics and transmission potential in mosquitoes. Importantly, faster maturation of outcrossed oocysts may maximize levels of recombination in transmitted malaria parasite populations.