The Monophyly of Nycteria and Polychromophilus Parasites A Missing Piece in the Evolution of Malaria and Other Haemosporida

Abstract

Haemosporida is a diverse order of vector-borne apicomplexan parasites infecting terrestrial vertebrates worldwide, including humans, but the evolutionary relationships among its genera remain unresolved. The phylogenetic placement of two bat-restricted genera, Nycteria and Polychromophilus, both of which lack erythrocytic schizogony, has varied across studies depending on taxon sampling and marker choice. To address this problem, an expanded dataset of near-complete mitochondrial (mtDNA) genomes together with nine nuclear loci were analyzed. Phylogenetic analyses of mtDNA recovered Nycteria and Polychromophilus as a strongly supported monophyletic clade. In contrast, analyses based only on the three mitochondrial coding genes (CDS) or a reduced nuclear dataset failed to recover their monophyly and showed low support and extensive topological conflict at deeper nodes. These results indicate that near-complete mitochondrial genomes recover phylogenetic signal that is not captured by reduced mitochondrial coding sequences or partial nuclear datasets. Molecular dating analyses further showed that divergence estimates for a putative Nycteria-Polychromophilus clade are compatible with the proposed times for bats diversification, and consistent with the broader haemosporidian timescale. When the Nycteria-Polychromophilus clade was incorporated as a calibration prior, divergence-time estimates became more precise without altering the overall evolutionary timeframe. Substantial mitochondrial gene-order rearrangements in a distinct Nycteria lineage were confirmed, highlighting structural divergence within this bat-associated group. In addition, heterogeneity in rates across mtDNA haemosporidian lineages was observed. Together, these findings support the existence of a distinct bat-associated clade whose deeper placement and evolutionary significance should be tested with broader phylogenomic sampling. Author SummaryMalaria parasites belong to a diverse group of organisms that infect many kinds of vertebrates, including birds, reptiles, and mammals (such as humans). Understanding how these parasites are related to each other is important for explaining how key biological traits have evolved. However, the relationships among major groups of haemosporidian parasites, including malaria parasites, remain unclear, particularly for those infecting bats. In this study, we focused on two groups of bat parasites, Nycteria and Polychromophilus, which share unusual biological features. The inferred evolutionary relationships of these two genera to other haemosporidians have been inconsistent across previous studies. By analyzing near-complete mitochondrial genomes, we found strong evidence that these two groups descended from a common evolutionary ancestor. In contrast, smaller datasets including nuclear genes failed to recover this relationship and produced conflicting results, suggesting that they lack sufficient information to resolve deep evolutionary relationships. We also found that this bat-associated lineage likely originated around the same time as early bats. In addition, we identified structural changes in the mitochondrial genome of one lineage, highlighting its evolutionary distinctiveness. Together, our results suggest that bats host a unique group of malaria parasites and demonstrate that more complete genetic data are essential for resolving their evolutionary history.