Comparative Chromosome Painting Clarifies the Intraspecific Chromosomal Variation in Two Ctenomys Species (Rodentia: Ctenomyidae).

BACKGROUND: Ctenomys is a subterranean rodent genus known for exhibiting the highest levels of chromosome variation, both among species (2n = 10 to 70) and within species. Ctenomys minutus is particularly notable for its extensive chromosomal diversity, comprising the greatest number of described cytotypes within this genus. In contrast, Ctenomys lami presents the highest degree of karyotypic variation within a comparatively restricted geographic range. Both species inhabit the coastal plain of southern Brazil: C. minutus occurs in dunes and sandy fields extending from Laguna (Santa Catarina State) to São José do Norte (Rio Grande do Sul State), whereas C. lami is restricted to the "Coxilha das Lombas" region, which lies parallel to the distribution of C. minutus in Rio Grande do Sul State. Despite their close evolutionary relationship and the absence of external morphological differences, the mechanism underlying their karyotypic divergence remains poorly understood. METHODS: In this study, we applied whole-chromosome painting using probes from Ctenomys flamarioni to investigate chromosomal evolution in C. minutus and C. lami. RESULTS: The resulting homology maps revealed a variety of chromosomal rearrangements that differentiate cytotypes both within and between these species. Comparative analyses demonstrated substantial karyotypic divergence from C. flamarioni, although some entire chromosomes and large chromosomal segments remained conserved between C. minutus and C. lami. Our findings underscore the critical role of chromosomal rearrangements in shaping the diversification of Ctenomys. Additionally, we identified shared chromosomal rearrangements in C. minutus and C. lami, which are likely restricted to the torquatus group. CONCLUSIONS: These rearrangements provide new insights into the processes driving chromosomal evolution in genus Ctenomys.