Chromosomal fusion and fission play a significant role in macroevolutionary processes, particularly in the speciation of Erebia butterflies. This study investigated the relationship between chromosomal rearrangements and speciation rates in Erebia, one of the most species-rich and karyotypically diverse butterfly groups. Using genome-based phylogeny and state-dependent birth-death models, the researchers found that anagenetic chromosomal changes (along phylogenetic branches) occur more frequently than cladogenetic changes (at speciation events). However, when cladogenetic changes do occur, they are mostly associated with chromosomal fissions rather than fusions. The relative importance of fusion and fission varies among Erebia clades, with younger, more karyotypically diverse clades showing a stronger association between speciation and chromosomal changes. Overall, the results suggest that chromosomal fusions and fissions have contrasting macroevolutionary roles, with fissions more likely to be involved in speciation events. The study also found that chromosomal changes are more prevalent in younger clades, such as the tyndarus clade, which has a high karyotype diversity. This clade shows a higher rate of cladogenetic chromosomal changes, particularly fissions, compared to other clades. The results indicate that chromosomal fusions and fissions may contribute to the diversification of Erebia, especially in clades with high karyotype diversity. The study used a combination of phylogenomic analysis and Bayesian models to infer the evolutionary history of Erebia and assess the impact of chromosomal rearrangements on speciation. The findings suggest that chromosomal fusions and fissions may play a significant role in the speciation of Erebia, with fissions being more commonly associated with speciation events. The study also highlights the importance of considering chromosomal evolution in understanding the macroevolutionary processes that drive speciation in Erebia and other butterfly groups.Chromosomal fusion and fission play a significant role in macroevolutionary processes, particularly in the speciation of Erebia butterflies. This study investigated the relationship between chromosomal rearrangements and speciation rates in Erebia, one of the most species-rich and karyotypically diverse butterfly groups. Using genome-based phylogeny and state-dependent birth-death models, the researchers found that anagenetic chromosomal changes (along phylogenetic branches) occur more frequently than cladogenetic changes (at speciation events). However, when cladogenetic changes do occur, they are mostly associated with chromosomal fissions rather than fusions. The relative importance of fusion and fission varies among Erebia clades, with younger, more karyotypically diverse clades showing a stronger association between speciation and chromosomal changes. Overall, the results suggest that chromosomal fusions and fissions have contrasting macroevolutionary roles, with fissions more likely to be involved in speciation events. The study also found that chromosomal changes are more prevalent in younger clades, such as the tyndarus clade, which has a high karyotype diversity. This clade shows a higher rate of cladogenetic chromosomal changes, particularly fissions, compared to other clades. The results indicate that chromosomal fusions and fissions may contribute to the diversification of Erebia, especially in clades with high karyotype diversity. The study used a combination of phylogenomic analysis and Bayesian models to infer the evolutionary history of Erebia and assess the impact of chromosomal rearrangements on speciation. The findings suggest that chromosomal fusions and fissions may play a significant role in the speciation of Erebia, with fissions being more commonly associated with speciation events. The study also highlights the importance of considering chromosomal evolution in understanding the macroevolutionary processes that drive speciation in Erebia and other butterfly groups.