Cytogenetic Characterization of Red-Fronted Coot (Fulica rufifrons Philippi & Landbeck, 1861) and Giant Wood Rail (Aramides ypecaha Vieillot, 1819) (Rallidae) and Implications for Avian Karyotype Evolution

Karyotypic diversification in birds is often masked by overall chromosomal conservation, yet the mechanisms driving lineage-specific variation remain poorly understood. Here, we demonstrate that genome evolution in Rallidae is shaped by dynamic, independent trajectories of chromosomal reorganization, despite the retention of general avian architectural features. By integrating cytogenetic and molecular mapping data from two Neotropical species, Fulica rufifrons Philippi & Landbeck, 1861 (Red-fronted Coot) and Aramides ypecaha Vieillot, 1819 (Giant Wood Rail), we show that repetitive DNA expansion and heterochromatinization contribute to karyotype variability and sex chromosome differentiation. The contrasting structure and heterochromatic composition of the W chromosome between these species reveal that sex chromosomes evolve rapidly and independently, driven by lineage-specific accumulation of repetitive elements. Moreover, the variation in microsatellite distribution, especially the distinct localization of motifs on macro- and microchromosomes, underscores the independent and dynamic evolution of repetitive sequences. Our findings collectively indicate that chromosomal rearrangements, along with the amplification and redistribution of repetitive DNA, are contributing factors of genomic diversification in Rallidae, offering new insights into the mechanisms underlying karyotype evolution and sex chromosome differentiation in birds.