Chromosomal fusion and fission in Erebia butterflies. The macroevolutionary role of chromosomal fusion and fission in Erebia butterflies

The impact of large-scale chromosomal rearrangements, such as fusions and fissions, on speciation is a long-standing conundrum. We assessed whether bursts of change in chromosome number resulting from fusion and fission are related to increased speciation rates in Erebia, one of the most diverse groups of European butterflies, both in karyotypes and taxonomically. We established a genome-based phylogeny and employed character state-dependent birth-death models to infer trajectories of karyotype evolution across Erebia. We demonstrate that rates of anagenetic (along phylogenetic branches) chromosomal change exceed cladogenetic (at speciation) change, but when cladogenetic changes occur, they are mostly fissions rather than fusions, highlighting their contrasting macroevolutionary patterns. Moreover, we found that the relative importance of fusion and fission differs among Erebia clades of different ages, where especially in younger, more karyotypically diverse clades speciation is frequently associated with chromosomal fusions. Overall, our results imply that large-scale chromosomal rearrangements play a macroevolutionary role, being associated with species diversification.