Mitochondrial DNA (mtDNA) sequencing has led to an unprecedented rise in the identification of cryptic species. However, it is widely acknowledged that nuclear DNA (nuDNA) sequence data are also necessary to properly define species boundaries. Next generation sequencing techniques provide a wealth of nuclear genomic data, which can be used to ascertain both the evolutionary history and taxonomic status of putative cryptic species. Here, we focus on the intriguing case of the butterfly Thymelicus sylvestris (Lepidoptera: Hesperiidae). We identified six deeply diverged mitochondrial lineages; three distributed all across Europe and found in sympatry, suggesting a potential case of cryptic species. We then sequenced these six lineages using double‐digest restriction‐site associated DNA sequencing (ddRADseq). Nuclear genomic loci contradicted mtDNA patterns and genotypes generally clustered according to geography, i.e., a pattern expected under the assumption of postglacial recolonization from different refugia. Further analyses indicated that this strong mtDNA/nuDNA discrepancy cannot be explained by incomplete lineage sorting, sex‐biased asymmetries, NUMTs, natural selection, introgression or Wolbachia‐mediated genetic sweeps. We suggest that this mitonuclear discordance was caused by long periods of geographic isolation followed by range expansions, homogenizing the nuclear but not the mitochondrial genome. These results highlight T. sylvestris as a potential case of multiple despeciation and/or lineage fusion events. We finally argue, since mtDNA and nuDNA do not necessarily follow the same mechanisms of evolution, their respective evolutionary history reflects complementary aspects of past demographic and biogeographic events.

Flowering plants emit complex bouquets of volatile organic compounds (VOCs) to mediate interactions with their pollinators. These bouquets are undoubtedly influenced by pollinator-mediated selection, particularly in deceptively-pollinated species that rely on chemical mimicry. However, many uncertainties remain regarding how spatially and temporally heterogeneous pollinators affect the diversity and distribution of floral odour variation. Here, we characterized and compared the floral odours of ten populations of deceptively-pollinated Arum maculatum (Araceae), and interannual and decadal variation in pollinator attraction within these populations. Additionally, we transplanted individuals from all sampled populations to two common garden sites dominated by different pollinator species (Psychoda phalaenoides or Psycha grisescens), and compared pollinator attraction rates to investigate whether populations maintained odour blends adapted to a specific pollinator. We identified high within-and among-population variation in a common blend of VOCs found across the range of A. maculatum. We also observed shifts in pollinator community composition within several populations over 1-2 years, as well as over the past decade. Common garden experiments further revealed that transplanted inflorescences generally attracted the dominant local pollinator species in both transplant sites. However, one population (Forêt du Gâvre, France) appears to exclusively attract P. grisescens, even when transplanted to a P. phalaenoides-dominated site. Together, our results suggest that maintaining diverse floral odour bouquets within populations may be advantageous when pollinator communities vary over short timescales. We propose that temporally-replicated ecological data are one potential key to understanding variation in complex traits such as floral odour, and in some cases may reveal resiliency to shifting pollinator communities.

Elevational gradients are useful ecological settings for revealing the biotic and abiotic drivers of plant trait variation and plant–insect interactions. However, most work focusing on plant defences has looked at individual traits and few studies have assessed multiple traits simultaneously, their correlated expression patterns, and abiotic factors associated with such patterns across elevations. To address this knowledge gap, we studied elevational variation in direct (phenolic compounds) and indirect (volatile organic compounds) constitutive defences and their inducibility after feeding by a specialist beetle Altica quercetorum in saplings of 18 wild populations of Quercus pyrenaica. We tested for: 1) clines in each defensive trait individually, 2) their patterns of correlated expression and 3) associations between any such clines and climatic factors. We found that constitutive direct defences (lignins and hydrolysable tannins) decreased with increasing elevation. We observed no elevational gradient for constitutive indirect defences (volatile organic compounds) or the inducibility of direct or indirect defensive traits when looking at groups of compounds. However, at individual tree‐level, increased induction of two monoterpenes (α‐fenchene and camphene) at higher elevation was shown. Furthermore, we show a significant pattern of co‐expression of constitutive and induced phenolics across populations, which weakened with increasing elevation. Finally, we found no evidence that climatic factors were associated with either individual or correlated trait expression patterns across elevations. Overall, these findings call for moving beyond elevational clines in individual plant defences, and argue that assessing elevational shifts in trait correlated expression patterns and their underlying mechanisms can increase our understanding of plant defence evolution and plant–herbivore interactions along environmental gradients.

Floral odor is a complex trait that mediates many biotic interactions, including pollination. While high intraspecific floral odor variation appears to be common, the ecological and evolutionary drivers of this variation are often unclear. Here, we investigated the influence of spatially and temporally heterogeneous pollinator communities on floral odor variation in Arum maculatum (Araceae). Through Europe-wide field surveys, we identified high floral odor diversity and shifts in the dominant pollinator species within several A. maculatum populations compared to pollinator data from the same sites ten years ago. Using common-garden experiments, we further confirmed that inflorescences from native and foreign pollinator backgrounds were equally efficient at attracting local pollinators. The substantial within-population floral odor variation we observed may therefore be advantageous when facing temporally heterogeneous pollinator communities. We propose spatio-temporal heterogeneity in pollinators as one potential mechanism maintaining diverse floral odor bouquets in angiosperms.

Bacterial symbionts are known to facilitate a wide range of physiological processes and ecological interactions for their hosts. In spite of this, caterpillars with highly diverse life histories appear to lack resident microbiota. Gut physiology, endogenous digestive enzymes, and limited social interactions may contribute to this pattern, but the consequences of shifts in social activity and diet on caterpillar microbiota are largely unknown. Phengaris alcon caterpillars undergo particularly dramatic social and dietary shifts when they parasitize Myrmica ant colonies, rapidly transitioning from solitary herbivory to ant tending (i.e., receiving protein‐rich regurgitations through trophallaxis). This unique life history provides a model for studying interactions between social living, diet, and caterpillar microbiota. Here, we characterized and compared bacterial communities within P . alcon caterpillars before and after their association with ants, using 16S rRNA amplicon sequencing and quantitative PCR. After being adopted by ants, bacterial communities within P. alcon caterpillars shifted substantially, with a significant increase in alpha diversity and greater consistency in bacterial community composition in terms of beta dissimilarity. We also characterized the bacterial communities within their host ants ( Myrmica schencki ), food plant ( Gentiana cruciata ), and soil from ant nest chambers. These data indicated that the aforementioned patterns were influenced by bacteria derived from caterpillars’ surrounding environments, rather than through transfers from ants. Thus, while bacterial communities are substantially reorganized over the life cycle of P. alcon caterpillars, it appears that they do not rely on transfers of bacteria from host ants to complete their development.