Foliar Spectral Signatures Reveal Adaptive Divergence in Section Virentes Across Species and Environmental Niches

Mariana S. Hernández Leal, J. Antonio Guzmán Q., Antonio González Rodríguez, and Jeannine Cavender-Bares

Published May 2026 in International Oaks No. 37: 195–204

Abstract

Genomic tools have transformed our understanding of species and population genetic structure in landscapes. However, discerning the impacts of neutral and adaptive evolutionary forces remains challenging, largely due to the scarcity of tools capable of measuring a broad spectrum of phenotypic traits. We assessed whether spectroscopic data from preserved leaves can detect phenotypic divergence across genetic and phylogenetic levels within and among populations of the seven species in Quercus section Virentes. The monophyletic lineage includes seven species that diversified under sympatric, parapatric, and allopatric speciation modes. We used 427 individuals to test the roles of isolation-by-distance (IBD) and isolation-by-environment (IBE), as well as the influences of selection versus phylogenetic inertia on traits. We also examined how phylogenetic signals are distributed across foliar reflectance spectra of leaves within the Virentes lineage. Partial redundancy analyses (pRDA) revealed that IBE explains more phenotypic variation than IBD among sympatric species, particularly in specific spectral regions. Across the phylogeny, phylogenetic generalized least square (PGLS) models show that environmental variables – especially minimum temperature of the coldest month and annual precipitation – predict traits related to cold tolerance, including lignin content and anthocyanin levels. These results demonstrate that spectral data can be used to capture adaptive differentiation and evolutionary history across scales, offering a powerful, non-destructive tool for linking phenotype, environment, and evolutionary processes in long-lived plant lineages.

Keywords

leaf spectroscopy, adaptive divergence, isolation-by-environment, phylogenetic signal, functional traits, live oaks, climate adaptation

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