Genomic Content in Avian Haemosporidian Parasites Suggests Co‐Regulation of Apicoplast and Mitochondrial Nucleoids

Precise quantification of the parasitic load during infections is necessary for a deep understanding of parasite-host interactions. Haemosporidians, an order of intracellular blood parasites, including agents of avian malaria and their closer relatives, have two organelles, remnants of endosymbiosis: the mitochondrion and the apicoplast, which have their own extranuclear genomes (nucleoids). While the number of organelles per parasitic cell appears to be stable, the number of their nucleoids is not, but the dynamics and factors affecting them still remain to be elucidated. We used a set of 71 blood samples of migratory birds infected by haemosporidian parasites to quantify relative DNA quantities of these two organelles through real-time quantitative PCR (qPCR). We investigated the congruence of these two parameters with the microscopically detected number of parasites, for all samples measured and for the subset of those with moderate to high parasitemia. We found that apicoplast DNA content was a better predictor for intermediate infection intensities, while mitochondrial DNA content was a better predictor for acute infections. This difference may result from the regulation of parasite intra- and inter-organellar genomic content throughout the infection stages in vertebrate hosts. Our work contributes to the methods for quantification of blood parasites in wildlife and to the understanding of their development and conservation-relevant consequences for the avian hosts.