Both geographical and ecological speciation interact during the evolution of a clade, but the relative contribution of these processes is rarely assessed for cold-dwelling biota. Here, we investigate the role of biogeography and the evolution of ecological traits on the diversification of the Holarctic arcto-alpine butterfly genus Oeneis (Lepidoptera: Satyrinae). We reconstructed the molecular phylogeny of the genus based on one mitochondrial (COI) and three nuclear (GAPDH, RpS5, wingless) genes. We inferred the biogeographical scenario and the ancestral state reconstructions of climatic and habitat requirements. Within the genus, we detected five main species groups corresponding to the taxonomic division and further paraphyletic position of Neominois (syn. n.). Next, we transferred O. aktashi from the hora to the polixenes species group on the bases of molecular relationships. We found that the genus originated in the dry grasslands of the mountains of Central Asia and dispersed over the Beringian Land Bridges to North America several times independently. Holarctic mountains, in particular the Asian Altai Mts. and Sayan Mts., host the oldest lineages and most of the species diversity. Arctic species are more recent, with Pliocene or Pleistocene origin. We detected a strong phylogenetic signal for the climatic niche, where one lineage diversified towards colder conditions. Altogether, our results indicate that both dispersal across geographical areas and occupation of distinct climatic niches promoted the diversification of the Oeneis genus..

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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 numbers resulting from chromosomal fusion and fission are related to increased speciation rates in Erebia, one of the most species-rich and karyotypically variable butterfly groups. We established a genome-based phylogeny and employed state-dependent birth-death models to infer trajectories of karyotype evolution across this genus. We demonstrate that rates of anagenetic chromosomal changes (i.e. along phylogenetic branches) exceed cladogenetic changes (i.e. at speciation events), but when cladogenetic changes occur, they are mostly associated with chromosomal fissions rather than fusions. 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 more frequently associated with chromosomal changes. Overall, our results imply that chromosomal fusions and fissions have contrasting macroevolutionary roles, and that large-scale chromosomal rearrangements are associated with bursts of species diversification.

The diversification of alpine species has been modulated by their climatic niches interacting with changing climatic conditions. The relative roles of climatic niche conservatism promoting geographical speciation and of climatic niche diversification are poorly understood in diverse temperate groups. Here, we investigate the climatic niche evolution in a species rich butterfly genus, Erebia (Dalman, 1816). This Holarctic cold-dwelling genus reaches the highest diversity in European mountains. We generated a nearly complete molecular phylogeny and modeled the climatic niche evolution using geo-referenced occurrence records. We reconstructed the evolution of the climatic niche and tested how the species’ climatic niche width changes across the occupied climate gradient and compared two main Erebia clades, the European and the Asian clade. We further explored climatic niche overlaps among species. Our analyses revealed that the evolution of Erebia has been shaped by climatic niche conservatism, supported by a strong phylogenetic signal and niche overlap in sister species, likely promoting allopatric speciation. The European and the Asian clades evolved their climatic niches toward different local optima. In addition, species in the European clade have narrower niches compared to the Asian clade. Contrasts among the clades may be related to regional climate differences, with lower climate seasonality in Europe compared to Central Asia favoring the evolution of narrower niches. Further, adaptive divergence could appear in other traits, such as habitat use, which can be reflected by narrower climatic niches detected in the European clade. Our study extends knowledge about the complexity of evolutionary drivers in temperate insects.