BACKGROUND AND AIMS: Crop wild relatives (CWR) are an important source for crop improvement, but they are often threatened by overharvesting and habitat fragmentation. This is the case for Agave angustifolia, one of the most important CWRs of cultivated agave species in the tequila and mezcal industries. Despite its cultural and economic importance, no range-wide genomic assessments exist for this species. METHODS: We analyzed double-digest genotyping-by-sequencing (GBS) data from 215 wild individuals from 67 populations spanning the entire Mexican distribution range of A. angustifolia. We combined newly generated data (97 individuals) with previously published sequences (118 individuals). We combined genomic data with species distribution models for past and future climatic scenarios, performed environmental association and genomic offset analyses, and tested spatial versus environmental drivers of differentiation. KEY RESULTS: In terms of climate and genomic offset, we found that although some populations-especially coastal ones-are expected to experience a considerable challenge adapting to changing environments, the species as a whole is likely to benefit from the warmer, drier conditions predicted by climate change projections. We identified specific wild populations that harbour climate-adapted alleles and are best positioned for persistence and crop improvement. While contemporary populations showed moderate-to-high genomic diversity, recent demographic impacts from wild harvest and local cultivation may not yet be detectable due to the species' long generation time and vegetative propagation. Genome-wide divergence among A. angustifolia populations was driven by Pleistocene climate oscillations and isolation-by-environment. CONCLUSIONS: Our study highlights both resilience and risk across the range of A. angustifolia, providing a comprehensive genetic framework for conserving its adaptive potential in the face of environmental change.
Abstract Background and Aims Quaternary climatic oscillations frequently promoted hybridisation and allopolyploid formation in temperate plants, yet well-documented examples from the European Alps remain scarce. Here, we investigated the origin of Daphne reichsteinii (Thymelaeaceae), a narrow endemic restricted to dolomite cliffs in the Southern Alps, and assessed its broader evolutionary significance. Methods We used an integrative approach combining phylogenomics, flow cytometry, karyological analyses, flow cytometric seed screening, and ecological niche modelling to test whether D. reichsteinii is of allopolyploid origin, identify its parental lineages, and assess its likely biogeographic history. We further assessed whether at least one of its parental lineages is also a narrow endemic, thereby evaluating the role of relict endemics as generators of evolutionary novelty rather than evolutionary dead ends. Key Results Our analyses confirm that D. reichsteinii is an allotetraploid derived from the widespread polyploid D. alpina as maternal parent and the diploid endemic D. petraea as paternal parent. Genomic data reveal pronounced subgenome asymmetry, with overrepresentation of the D. alpina subgenome. Seed-screening results are consistent with apomictic reproduction, suggesting that apomixis may occur in Daphne. Niche modelling indicates that D. reichsteinii occupies a climatic niche distinct from those of both parents and suggests that suitable habitats likely persisted in the Lake Garda region during the Last Glacial Maximum. Conclusions Our results indicate that the peri-Alpine Lake Garda region acted both as a refugium and as a zone of secondary contact, facilitating allopolyploid speciation. More broadly, the study shows that a Tertiary relict endemic can remain evolutionarily active and contribute to the origin of new endemic lineages.
BACKGROUND AND AIMS Stomatal and leaf venation traits are important structural components associated with plant gas exchange and water transport, but their variation along environmental gradients may depend on plant functional strategies. We investigated whether stomatal and vein traits exhibit coordinated yet trait-specific patterns across an elevational gradient, and whether such patterns vary with leaf habit and growth form in a subtropical forest. METHODS We examined 12 woody species distributed along a 300-1360 m elevational gradient on Lushan Mountain, China. Stomatal length (SL), stomatal density (SD), and vein density (VD) were quantified from cleared leaves, with species × elevation means used as observational units. Linear mixed-effects models were applied to evaluate associations of traits with elevation, leaf habit (evergreen vs. deciduous), and growth form (shrub vs. tree), and to test elevation-dependent variation in the SD-VD relationship. KEY RESULTS Stomatal length and stomatal density showed no significant elevational trends, whereas vein density increased with elevation, indicating contrasting responses among leaf anatomical traits. Stomatal density differed among combinations of leaf habit and growth form, with a significant leaf habit × growth form interaction and higher SD in deciduous trees than in other groups. Across species and elevations, SD was positively associated with VD, but the strength of this relationship varied nonlinearly along the gradient, with the strongest association occurring at intermediate elevations (∼800 m) corresponding to the evergreen-deciduous mixed forest zone. CONCLUSIONS Our findings demonstrate that elevation does not generate uniform changes across leaf anatomical traits. Instead, trait variation depends on environmental context and functional strategies, with leaf habit and growth form jointly influencing stomatal density and stomatal-vein coordination. Considering trait relationships in addition to individual traits provides new insights into how plants organize leaf structure across heterogeneous environments.
