Detalle de: Full ribosomal RNA gene arrays confirm Marteilia refringens sensu stricto and Marteilia pararefringens as separate species, and assess the validity of current diagnostic regions

The species boundary between the paramyxid parasitic protists Marteilia refringens sensu stricto and Marteilia pararefringens has been disputed, and their classification as separate species has been a topic of debate for the past 2 decades. Originally described as separate species, they were later synonymized based on limited evidence and referred to as 2 types of M. refringens (O-type and M-type). In 2018, longer rRNA gene sequences from a small number of samples supported their reclassification as distinct species. However, limited sample sizes and incomplete array coverage left questions regarding the robustness of this separation. We present full transcribed ribosomal RNA (rRNA) gene arrays from a broad set of Marteilia samples collected across their known host and geographic ranges. Phylogenetic and species delimitation analysis of these sequences robustly distinguished M. refringens sensu stricto from M. pararefringens . We identified sites across the entire rRNA array with consistent sequence differences between species and carried out phylogenetic analyses on the most variable regions of the rRNA array (ITS1 and ETS), which also distinguished between the 2 species. We also provide new evidence for distinct host preference profiles for M. refringens sensu stricto and M. pararefringens. The results support the recognition of M. refringens sensu stricto and M. pararefringens as separate species and identify robust markers for their detection, allowing a better understanding of their respective ecologies, host preference, pathogenicity and life cycle. The study also lays a foundation for future genomic comparisons to explore evolutionary divergence and diagnostic marker development beyond the rRNA array.