Understanding how speciation relates to ecological divergence has long fascinated biologists. It is assumed that ecological divergence is essential to sympatric speciation, as a mechanism to avoid competition and eventually lead to reproductive isolation, while divergence in allopatry is not necessarily associated with niche differentiation. The impact of the spatial context of divergence on the evolutionary rates of abiotic dimensions of the ecological niche has rarely been explored for an entire clade. Here, we compare the magnitude of climatic niche shifts between sympatric versus allopatric divergence of lineages in butterflies. By combining next-generation sequencing, parametric biogeography and ecological niche analyses applied to a genus-wide phylogeny of PalaearcticPyrgusbutterflies, we compare evolutionary rates along eight climatic dimensions across sister lineages that diverged in large-scale sympatry versus allopatry. In order to examine the possible effects of the spatial scale at which sympatry is defined, we considered three sets of biogeographic assignments, ranging from narrow to broad definition. Our findings suggest higher rates of niche evolution along all climatic dimensions for sister lineages that diverge in sympatry, when using a narrow delineation of biogeographic areas. This result contrasts with significantly lower rates of climatic niche evolution found in cases of allopatric speciation, despite the biogeographic regions defined here being characterized by significantly different climates. Higher rates in allopatry are retrieved when biogeographic areas are too widely defined—in such a case allopatric events may be recorded as sympatric. Our results reveal the macro-evolutionary significance of abiotic niche differentiation involved in speciation processes within biogeographic regions, and illustrate the importance of the spatial scale chosen to define areas when applying parametric biogeographic analyses.

Summary

• Crassulacean acid metabolism (

  CAM
  ) photosynthesis is an adaptation to water and atmospheric
  CO
  ₂ deficits that has been linked to diversification in dry‐adapted plants. We investigated whether
  CAM
  evolution can be associated with the availability of new or alternative niches, using Eulophiinae orchids as a case study.

• Carbon isotope ratios, geographical and climate data, fossil records and

  DNA
  sequences were used to: assess the prevalence of
  CAM
  in Eulophiinae orchids; characterize the ecological niche of extant taxa; infer divergence times; and estimate whether
  CAM
  is associated with niche shifts.

• CAM
  evolved in four terrestrial lineages during the late Miocene/Pliocene, which have uneven diversification patterns. These lineages originated in humid habitats and colonized dry/seasonally dry environments in Africa and Madagascar. Additional key features (variegation, heterophylly) evolved in the most species‐rich
  CAM
  lineages. Dry habitats were also colonized by a lineage that includes putative mycoheterotrophic taxa.

• These findings indicate that the switch to

  CAM
  is associated with environmental change. With its suite of adaptive traits, this group of orchids represents a unique opportunity to study the adaptations to dry environments, especially in the face of projected global aridification.

Aim  To predict the fate of alpine interactions involving specialized species, using a monophagous beetle and its host plant as a case study.

Location  The Alps.

Methods  We investigated genetic structuring of the herbivorous beetle Oreina gloriosa and its specific host‐plant Peucedanum ostruthium. We used genome fingerprinting (in the insect and the plant) and sequence data (in the insect) to compare the distribution of the main gene pools in the two associated species and to estimate divergence time in the insect, a proxy for the temporal origin of the interaction. We quantified the similarity in spatial genetic structures by performing a Procrustes analysis, a tool from shape theory. Finally, we simulated recolonization of an empty space analogous to the deglaciated Alps just after ice retreat by two lineages from two species showing unbalanced dependence, to examine how timing of the recolonization process, as well as dispersal capacities of associated species, could explain the observed pattern.

Results  Contrasting with expectations based on their asymmetrical dependence, patterns in the beetle and plant were congruent at a large scale. Exceptions occurred at a regional scale in areas of admixture, matching known suture zones in Alpine plants. Simulations using a lattice‐based model suggested these empirical patterns arose during or soon after recolonization, long after the estimated origin of the interaction c. 0.5 million years ago.

Main conclusions  Species‐specific interactions are scarce in alpine habitats because glacial cycles have limited the opportunities for co‐evolution. Their fate, however, remains uncertain under climate change. Here we show that whereas most dispersal routes are paralleled at a large scale, regional incongruence implies that the destinies of the species might differ under changing climate. This may be a consequence of the host dependence of the beetle, which locally limits the establishment of dispersing insects.

Background

Within the Coleoptera, the largest order in the animal kingdom, the exclusively herbivorous Chrysomelidae are recognized as one of the most species rich beetle families. The evolutionary processes that have fueled radiation into the more than thirty-five thousand currently recognized leaf beetle species remain partly unresolved. The prominent role of leaf beetles in the insect world, their omnipresence across all terrestrial biomes and their economic importance as common agricultural pest organisms make this family particularly interesting for studying the mechanisms that drive diversification. Here we specifically focus on two ecotypes of the alpine leaf beetleOreina speciosissima(Scop.), which have been shown to exhibit morphological differences in male genitalia roughly corresponding to the subspeciesOreina speciosissima sensu strictoandOreina speciosissima troglodytes. In general the two ecotypes segregate along an elevation gradient and by host plants:Oreina speciosissima sensu strictocolonizes high forb vegetation at low altitude andOreina speciosissima troglodytesis found in stone run vegetation at higher elevations. Both host plants and leaf beetles have a patchy geographical distribution. Through use of gene sequencing and genome fingerprinting (AFLP) we analyzed the genetic structure and habitat use ofOreina speciosissimapopulations from the Swiss Alps to examine whether the two ecotypes have a genetic basis. By investigating a wide range of altitudes and focusing on the structuring effect of habitat types, we aim to provide answers regarding the factors that drive adaptive radiation in this phytophagous leaf beetle.