Supplementary Material for: Variation and morphological manifestation of germline restricted chromosomes in three species of leaf warblers of genus Phylloscopus

Introduction: Germline restricted chromosomes are considered as a rather ancient element in the genomes of passerine birds. Obviously, detailed comparative studies on model groups including closely related species are required for a better understanding of GRC evolution. It is especially interesting if GRCs in such closely related species have acquired significant differences. Methods: Analysis of synaptonemal complexes in spread nuclei of primary spermatocytes using immunocytochemical techniques and fluorescent microscopy were applied. Results: Therefore, in this work we compared three taxonomically close species of the genus Phylloscopus: Ph. sindianus lorenzii, Ph. collybita menzbieri and Ph. nitidus, with differences in morphological manifestation of GRCs: macro- and micro-GRCs. We were able to trace the morphological transformations of macro-GRC at stages from leptotene to diplotene, and describe the complex structure of this chromosome in Ph. nitidus. Conclusion: We hope that the taxonomic group under study can become a convenient model for comparative studies of GRCs in closely related species in order to understand the evolution of these unusual chromosomes.